53 files changed, 1266 insertions, 322 deletions
diff --git a/Cargo.lock b/Cargo.lock
index a3887ce99..9a1a05683 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -11,9 +11,9 @@ dependencies = [
 [[package]]
 name = "anyhow"
-version = "1.0.27"
+version = "1.0.28"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "013a6e0a2cbe3d20f9c60b65458f7a7f7a5e636c5d0f45a5a6aee5d4b1f01785"
+checksum = "d9a60d744a80c30fcb657dfe2c1b22bcb3e814c1a1e3674f32bf5820b570fbff"
 [[package]]
 name = "anymap"
@@ -435,9 +435,9 @@ dependencies = [
 [[package]]
 name = "hermit-abi"
-version = "0.1.8"
+version = "0.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1010591b26bbfe835e9faeabeb11866061cc7dcebffd56ad7d0942d0e61aefd8"
+checksum = "725cf19794cf90aa94e65050cb4191ff5d8fa87a498383774c47b332e3af952e"
 dependencies = [
 "libc",
 ]
@@ -792,9 +792,9 @@ dependencies = [
 [[package]]
 name = "paste"
-version = "0.1.8"
+version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8292c1e1e81ddb552c4c90c36af201a0ce7e34995f55f0480f01052f242811c9"
+checksum = "092d791bf7847f70bbd49085489fba25fc2c193571752bff9e36e74e72403932"
 dependencies = [
 "paste-impl",
 "proc-macro-hack",
@@ -802,9 +802,9 @@ dependencies = [
 [[package]]
 name = "paste-impl"
-version = "0.1.8"
+version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5e9c43f2645f06ee452544ad032886a75f3d1797b9487dcadcae9100ba58a51c"
+checksum = "406c23fb4c45cc6f68a9bbabb8ec7bd6f8cfcbd17e9e8f72c2460282f8325729"
 dependencies = [
 "proc-macro-hack",
 "proc-macro2",
@@ -848,9 +848,9 @@ checksum = "fcfdefadc3d57ca21cf17990a28ef4c0f7c61383a28cb7604cf4a18e6ede1420"
 [[package]]
 name = "proc-macro2"
-version = "1.0.9"
+version = "1.0.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6c09721c6781493a2a492a96b5a5bf19b65917fe6728884e7c44dd0c60ca3435"
+checksum = "df246d292ff63439fea9bc8c0a270bed0e390d5ebd4db4ba15aba81111b5abe3"
 dependencies = [
 "unicode-xid",
 ]
@@ -887,19 +887,6 @@ dependencies = [
 ]
 [[package]]
-name = "ra_cargo_watch"
-version = "0.1.0"
-dependencies = [
- "cargo_metadata",
- "crossbeam-channel",
- "insta",
- "jod-thread",
- "log",
- "lsp-types",
- "serde_json",
-]
-[[package]]
 name = "ra_cfg"
 version = "0.1.0"
 dependencies = [
@@ -924,6 +911,19 @@ dependencies = [
 ]
 [[package]]
+name = "ra_flycheck"
+version = "0.1.0"
+dependencies = [
+ "cargo_metadata",
+ "crossbeam-channel",
+ "insta",
+ "jod-thread",
+ "log",
+ "lsp-types",
+ "serde_json",
+]
+[[package]]
 name = "ra_fmt"
 version = "0.1.0"
 dependencies = [
@@ -1075,7 +1075,12 @@ dependencies = [
 name = "ra_proc_macro"
 version = "0.1.0"
 dependencies = [
+ "crossbeam-channel",
+ "jod-thread",
+ "log",
 "ra_tt",
+ "serde",
+ "serde_json",
 ]
 [[package]]
@@ -1096,7 +1101,6 @@ dependencies = [
 "cargo_metadata",
 "log",
 "ra_arena",
- "ra_cargo_watch",
 "ra_cfg",
 "ra_db",
 "ra_proc_macro",
@@ -1295,8 +1299,8 @@ dependencies = [
 "lsp-types",
 "parking_lot",
 "pico-args",
- "ra_cargo_watch",
 "ra_db",
+ "ra_flycheck",
 "ra_hir",
 "ra_hir_def",
 "ra_hir_ty",
@@ -1426,9 +1430,9 @@ dependencies = [
 [[package]]
 name = "serde_json"
-version = "1.0.48"
+version = "1.0.50"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9371ade75d4c2d6cb154141b9752cf3781ec9c05e0e5cf35060e1e70ee7b9c25"
+checksum = "78a7a12c167809363ec3bd7329fc0a3369056996de43c4b37ef3cd54a6ce4867"
 dependencies = [
 "itoa",
 "ryu",
@@ -1651,9 +1655,9 @@ checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
 [[package]]
 name = "winapi-util"
-version = "0.1.3"
+version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4ccfbf554c6ad11084fb7517daca16cfdcaccbdadba4fc336f032a8b12c2ad80"
+checksum = "fa515c5163a99cc82bab70fd3bfdd36d827be85de63737b40fcef2ce084a436e"
 dependencies = [
 "winapi 0.3.8",
 ]
diff --git a/crates/ra_arena/src/map.rs b/crates/ra_arena/src/map.rs
index 5e764113d..0f33907c0 100644
--- a/crates/ra_arena/src/map.rs
+++ b/crates/ra_arena/src/map.rs
@@ -14,14 +14,8 @@ pub struct ArenaMap<ID, V> {
 impl<T, V> ArenaMap<Idx<T>, V> {
    pub fn insert(&mut self, id: Idx<T>, t: V) {
        let idx = Self::to_idx(id);
-        if self.v.capacity() <= idx {
-            self.v.reserve(idx + 1 - self.v.capacity());
+        self.v.resize_with((idx + 1).max(self.v.len()), || None);
-        }
-        if self.v.len() <= idx {
-            while self.v.len() <= idx {
-                self.v.push(None);
-            }
-        }
        self.v[idx] = Some(t);
    }
diff --git a/crates/ra_assists/src/handlers/fill_match_arms.rs b/crates/ra_assists/src/handlers/fill_match_arms.rs
index 41bb97928..8d1af9933 100644
--- a/crates/ra_assists/src/handlers/fill_match_arms.rs
+++ b/crates/ra_assists/src/handlers/fill_match_arms.rs
@@ -1,15 +1,11 @@
-//! FIXME: write short doc here
 use std::iter;
 use hir::{Adt, HasSource, ModuleDef, Semantics};
 use itertools::Itertools;
 use ra_ide_db::RootDatabase;
+use ra_syntax::ast::{self, make, AstNode, MatchArm, NameOwner, Pat};
 use crate::{Assist, AssistCtx, AssistId};
-use ra_syntax::ast::{self, make, AstNode, NameOwner};
-use ast::{MatchArm, Pat};
 // Assist: fill_match_arms
 //
@@ -717,4 +713,28 @@ mod tests {
            "#,
        );
    }
+    #[test]
+    fn fill_match_arms_placeholder() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A { One, Two, }
+            fn foo(a: A) {
+                match a<|> {
+                    _ => (),
+                }
+            }
+            "#,
+            r#"
+            enum A { One, Two, }
+            fn foo(a: A) {
+                match <|>a {
+                    A::One => {}
+                    A::Two => {}
+                }
+            }
+            "#,
+        );
+    }
 }
diff --git a/crates/ra_cargo_watch/Cargo.toml b/crates/ra_flycheck/Cargo.toml
index 300033a18..c9a9ddc12 100644
--- a/crates/ra_cargo_watch/Cargo.toml
+++ b/crates/ra_flycheck/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 edition = "2018"
-name = "ra_cargo_watch"
+name = "ra_flycheck"
 version = "0.1.0"
 authors = ["rust-analyzer developers"]
diff --git a/crates/ra_cargo_watch/src/conv.rs b/crates/ra_flycheck/src/conv.rs
index 817543deb..817543deb 100644
--- a/crates/ra_cargo_watch/src/conv.rs
+++ b/crates/ra_flycheck/src/conv.rs
diff --git a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_clippy_pass_by_ref.snap b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_clippy_pass_by_ref.snap
index a59fa84fa..4c9db0385 100644
--- a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_clippy_pass_by_ref.snap
+++ b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_clippy_pass_by_ref.snap
@@ -1,5 +1,5 @@
 ---
-source: crates/ra_cargo_watch/src/conv/test.rs
+source: crates/ra_flycheck/src/conv/test.rs
 expression: diag
 ---
 [
diff --git a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_handles_macro_location.snap b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_handles_macro_location.snap
index 61ae0c9ae..7cde4d867 100644
--- a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_handles_macro_location.snap
+++ b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_handles_macro_location.snap
@@ -1,5 +1,5 @@
 ---
-source: crates/ra_cargo_watch/src/conv/test.rs
+source: crates/ra_flycheck/src/conv/test.rs
 expression: diag
 ---
 [
diff --git a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_macro_compiler_error.snap b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_macro_compiler_error.snap
index 641da1a58..1cc37e087 100644
--- a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_macro_compiler_error.snap
+++ b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_macro_compiler_error.snap
@@ -1,5 +1,5 @@
 ---
-source: crates/ra_cargo_watch/src/conv/test.rs
+source: crates/ra_flycheck/src/conv/test.rs
 expression: diag
 ---
 [
diff --git a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_multi_line_fix.snap b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_multi_line_fix.snap
index 0557a2e79..615ed8378 100644
--- a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_multi_line_fix.snap
+++ b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_multi_line_fix.snap
@@ -1,5 +1,5 @@
 ---
-source: crates/ra_cargo_watch/src/conv/test.rs
+source: crates/ra_flycheck/src/conv/test.rs
 expression: diag
 ---
 [
diff --git a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_incompatible_type_for_trait.snap b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_rustc_incompatible_type_for_trait.snap
index 754bc33a4..0df0fce18 100644
--- a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_incompatible_type_for_trait.snap
+++ b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_rustc_incompatible_type_for_trait.snap
@@ -1,5 +1,5 @@
 ---
-source: crates/ra_cargo_watch/src/conv/test.rs
+source: crates/ra_flycheck/src/conv/test.rs
 expression: diag
 ---
 [
diff --git a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_mismatched_type.snap b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_rustc_mismatched_type.snap
index 78b7f7cc8..28ebcb3b3 100644
--- a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_mismatched_type.snap
+++ b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_rustc_mismatched_type.snap
@@ -1,5 +1,5 @@
 ---
-source: crates/ra_cargo_watch/src/conv/test.rs
+source: crates/ra_flycheck/src/conv/test.rs
 expression: diag
 ---
 [
diff --git a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_unused_variable.snap b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_rustc_unused_variable.snap
index 5989ed202..5e0873281 100644
--- a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_unused_variable.snap
+++ b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_rustc_unused_variable.snap
@@ -1,5 +1,5 @@
 ---
-source: crates/ra_cargo_watch/src/conv/test.rs
+source: crates/ra_flycheck/src/conv/test.rs
 expression: diag
 ---
 [
diff --git a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_wrong_number_of_parameters.snap b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_rustc_wrong_number_of_parameters.snap
index e34b546dc..e500d3cd6 100644
--- a/crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_wrong_number_of_parameters.snap
+++ b/crates/ra_flycheck/src/conv/snapshots/ra_flycheck__conv__test__snap_rustc_wrong_number_of_parameters.snap
@@ -1,5 +1,5 @@
 ---
-source: crates/ra_cargo_watch/src/conv/test.rs
+source: crates/ra_flycheck/src/conv/test.rs
 expression: diag
 ---
 [
diff --git a/crates/ra_cargo_watch/src/conv/test.rs b/crates/ra_flycheck/src/conv/test.rs
index 4e81455ca..4e81455ca 100644
--- a/crates/ra_cargo_watch/src/conv/test.rs
+++ b/crates/ra_flycheck/src/conv/test.rs
diff --git a/crates/ra_cargo_watch/src/lib.rs b/crates/ra_flycheck/src/lib.rs
index 2692c1bf5..38940a77b 100644
--- a/crates/ra_cargo_watch/src/lib.rs
+++ b/crates/ra_flycheck/src/lib.rs
@@ -22,7 +22,7 @@ use crate::conv::{map_rust_diagnostic_to_lsp, MappedRustDiagnostic};
 pub use crate::conv::url_from_path_with_drive_lowercasing;
 #[derive(Clone, Debug)]
-pub struct CheckOptions {
+pub struct CheckConfig {
    pub enable: bool,
    pub args: Vec<String>,
    pub command: String,
@@ -42,13 +42,11 @@ pub struct CheckWatcher {
 }
 impl CheckWatcher {
-    pub fn new(options: &CheckOptions, workspace_root: PathBuf) -> CheckWatcher {
+    pub fn new(config: CheckConfig, workspace_root: PathBuf) -> CheckWatcher {
-        let options = options.clone();
        let (task_send, task_recv) = unbounded::<CheckTask>();
        let (cmd_send, cmd_recv) = unbounded::<CheckCommand>();
        let handle = jod_thread::spawn(move || {
-            let mut check = CheckWatcherThread::new(options, workspace_root);
+            let mut check = CheckWatcherThread::new(config, workspace_root);
            check.run(&task_send, &cmd_recv);
        });
        CheckWatcher { task_recv, cmd_send, handle: Some(handle) }
@@ -78,14 +76,14 @@ pub enum CheckCommand {
 }
 struct CheckWatcherThread {
-    options: CheckOptions,
+    options: CheckConfig,
    workspace_root: PathBuf,
    watcher: WatchThread,
    last_update_req: Option<Instant>,
 }
 impl CheckWatcherThread {
-    fn new(options: CheckOptions, workspace_root: PathBuf) -> CheckWatcherThread {
+    fn new(options: CheckConfig, workspace_root: PathBuf) -> CheckWatcherThread {
        CheckWatcherThread {
            options,
            workspace_root,
@@ -245,7 +243,7 @@ impl fmt::Display for CargoError {
 }
 impl error::Error for CargoError {}
-pub fn run_cargo(
+fn run_cargo(
    args: &[String],
    current_dir: Option<&Path>,
    on_message: &mut dyn FnMut(cargo_metadata::Message) -> bool,
@@ -324,7 +322,7 @@ impl WatchThread {
        WatchThread { message_recv: never(), _handle: None }
    }
-    fn new(options: &CheckOptions, workspace_root: &Path) -> WatchThread {
+    fn new(options: &CheckConfig, workspace_root: &Path) -> WatchThread {
        let mut args: Vec<String> = vec![
            options.command.clone(),
            "--workspace".to_string(),
diff --git a/crates/ra_hir_expand/src/proc_macro.rs b/crates/ra_hir_expand/src/proc_macro.rs
index 4d270e0de..97d1208ec 100644
--- a/crates/ra_hir_expand/src/proc_macro.rs
+++ b/crates/ra_hir_expand/src/proc_macro.rs
@@ -9,6 +9,15 @@ pub struct ProcMacroExpander {
    proc_macro_id: ProcMacroId,
 }
+macro_rules! err {
+    ($fmt:literal, $($tt:tt),*) => {
+        mbe::ExpandError::ProcMacroError(tt::ExpansionError::Unknown(format!($fmt, $($tt),*)))
+    };
+    ($fmt:literal) => {
+        mbe::ExpandError::ProcMacroError(tt::ExpansionError::Unknown($fmt.to_string()))
+    }
+}
 impl ProcMacroExpander {
    pub fn new(krate: CrateId, proc_macro_id: ProcMacroId) -> ProcMacroExpander {
        ProcMacroExpander { krate, proc_macro_id }
@@ -25,8 +34,24 @@ impl ProcMacroExpander {
            .proc_macro
            .get(self.proc_macro_id.0 as usize)
            .clone()
-            .ok_or_else(|| mbe::ExpandError::ConversionError)?;
+            .ok_or_else(|| err!("No derive macro found."))?;
+        let tt = remove_derive_atr(tt, &proc_macro.name)
+            .ok_or_else(|| err!("Fail to remove derive for custom derive"))?;
        proc_macro.expander.expand(&tt, None).map_err(mbe::ExpandError::from)
    }
 }
+fn remove_derive_atr(tt: &tt::Subtree, _name: &str) -> Option<tt::Subtree> {
+    // FIXME: proper handle the remove derive
+    // We assume the first 2 tokens are #[derive(name)]
+    if tt.token_trees.len() > 2 {
+        let mut tt = tt.clone();
+        tt.token_trees.remove(0);
+        tt.token_trees.remove(0);
+        return Some(tt);
+    }
+    None
+}
diff --git a/crates/ra_ide/src/completion.rs b/crates/ra_ide/src/completion.rs
index cd0757be5..b683572fb 100644
--- a/crates/ra_ide/src/completion.rs
+++ b/crates/ra_ide/src/completion.rs
@@ -34,15 +34,15 @@ pub use crate::completion::completion_item::{
 };
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub struct CompletionOptions {
+pub struct CompletionConfig {
    pub enable_postfix_completions: bool,
    pub add_call_parenthesis: bool,
    pub add_call_argument_snippets: bool,
 }
-impl Default for CompletionOptions {
+impl Default for CompletionConfig {
    fn default() -> Self {
-        CompletionOptions {
+        CompletionConfig {
            enable_postfix_completions: true,
            add_call_parenthesis: true,
            add_call_argument_snippets: true,
@@ -75,9 +75,9 @@ impl Default for CompletionOptions {
 pub(crate) fn completions(
    db: &RootDatabase,
    position: FilePosition,
-    options: &CompletionOptions,
+    config: &CompletionConfig,
 ) -> Option<Completions> {
-    let ctx = CompletionContext::new(db, position, options)?;
+    let ctx = CompletionContext::new(db, position, config)?;
    let mut acc = Completions::default();
diff --git a/crates/ra_ide/src/completion/complete_postfix.rs b/crates/ra_ide/src/completion/complete_postfix.rs
index 0a00054b2..29c2881c6 100644
--- a/crates/ra_ide/src/completion/complete_postfix.rs
+++ b/crates/ra_ide/src/completion/complete_postfix.rs
@@ -15,7 +15,7 @@ use crate::{
 };
 pub(super) fn complete_postfix(acc: &mut Completions, ctx: &CompletionContext) {
-    if !ctx.options.enable_postfix_completions {
+    if !ctx.config.enable_postfix_completions {
        return;
    }
diff --git a/crates/ra_ide/src/completion/completion_context.rs b/crates/ra_ide/src/completion/completion_context.rs
index 319e33b61..fdc0da2c5 100644
--- a/crates/ra_ide/src/completion/completion_context.rs
+++ b/crates/ra_ide/src/completion/completion_context.rs
@@ -11,7 +11,7 @@ use ra_syntax::{
 };
 use ra_text_edit::AtomTextEdit;
-use crate::{completion::CompletionOptions, FilePosition};
+use crate::{completion::CompletionConfig, FilePosition};
 /// `CompletionContext` is created early during completion to figure out, where
 /// exactly is the cursor, syntax-wise.
@@ -19,7 +19,7 @@ use crate::{completion::CompletionOptions, FilePosition};
 pub(crate) struct CompletionContext<'a> {
    pub(super) sema: Semantics<'a, RootDatabase>,
    pub(super) db: &'a RootDatabase,
-    pub(super) options: &'a CompletionOptions,
+    pub(super) config: &'a CompletionConfig,
    pub(super) offset: TextUnit,
    /// The token before the cursor, in the original file.
    pub(super) original_token: SyntaxToken,
@@ -61,7 +61,7 @@ impl<'a> CompletionContext<'a> {
    pub(super) fn new(
        db: &'a RootDatabase,
        position: FilePosition,
-        options: &'a CompletionOptions,
+        config: &'a CompletionConfig,
    ) -> Option<CompletionContext<'a>> {
        let sema = Semantics::new(db);
@@ -85,7 +85,7 @@ impl<'a> CompletionContext<'a> {
        let mut ctx = CompletionContext {
            sema,
            db,
-            options,
+            config,
            original_token,
            token,
            offset: position.offset,
diff --git a/crates/ra_ide/src/completion/presentation.rs b/crates/ra_ide/src/completion/presentation.rs
index 60f1b83f3..1c7c0924d 100644
--- a/crates/ra_ide/src/completion/presentation.rs
+++ b/crates/ra_ide/src/completion/presentation.rs
@@ -106,7 +106,7 @@ impl Completions {
        };
        // Add `<>` for generic types
-        if ctx.is_path_type && !ctx.has_type_args && ctx.options.add_call_parenthesis {
+        if ctx.is_path_type && !ctx.has_type_args && ctx.config.add_call_parenthesis {
            let has_non_default_type_params = match resolution {
                ScopeDef::ModuleDef(Adt(it)) => it.has_non_default_type_params(ctx.db),
                ScopeDef::ModuleDef(TypeAlias(it)) => it.has_non_default_type_params(ctx.db),
@@ -211,14 +211,14 @@ impl Completions {
                .detail(function_signature.to_string());
        // If not an import, add parenthesis automatically.
-        if ctx.use_item_syntax.is_none() && !ctx.is_call && ctx.options.add_call_parenthesis {
+        if ctx.use_item_syntax.is_none() && !ctx.is_call && ctx.config.add_call_parenthesis {
            tested_by!(inserts_parens_for_function_calls);
            let (snippet, label) = if params.is_empty() || has_self_param && params.len() == 1 {
                (format!("{}()$0", name), format!("{}()", name))
            } else {
                builder = builder.trigger_call_info();
-                let snippet = if ctx.options.add_call_argument_snippets {
+                let snippet = if ctx.config.add_call_argument_snippets {
                    let to_skip = if has_self_param { 1 } else { 0 };
                    let function_params_snippet = function_signature
                        .parameter_names
@@ -311,7 +311,7 @@ mod tests {
    use crate::completion::{
        test_utils::{do_completion, do_completion_with_options},
-        CompletionItem, CompletionKind, CompletionOptions,
+        CompletionConfig, CompletionItem, CompletionKind,
    };
    fn do_reference_completion(ra_fixture: &str) -> Vec<CompletionItem> {
@@ -320,7 +320,7 @@ mod tests {
    fn do_reference_completion_with_options(
        ra_fixture: &str,
-        options: CompletionOptions,
+        options: CompletionConfig,
    ) -> Vec<CompletionItem> {
        do_completion_with_options(ra_fixture, CompletionKind::Reference, &options)
    }
@@ -589,7 +589,7 @@ mod tests {
                    s.f<|>
                }
                ",
-                CompletionOptions {
+                CompletionConfig {
                    add_call_argument_snippets: false,
                    .. Default::default()
                }
diff --git a/crates/ra_ide/src/completion/test_utils.rs b/crates/ra_ide/src/completion/test_utils.rs
index 136857315..eb90b5279 100644
--- a/crates/ra_ide/src/completion/test_utils.rs
+++ b/crates/ra_ide/src/completion/test_utils.rs
@@ -1,19 +1,19 @@
 //! Runs completion for testing purposes.
 use crate::{
-    completion::{completion_item::CompletionKind, CompletionOptions},
+    completion::{completion_item::CompletionKind, CompletionConfig},
    mock_analysis::{analysis_and_position, single_file_with_position},
    CompletionItem,
 };
 pub(crate) fn do_completion(code: &str, kind: CompletionKind) -> Vec<CompletionItem> {
-    do_completion_with_options(code, kind, &CompletionOptions::default())
+    do_completion_with_options(code, kind, &CompletionConfig::default())
 }
 pub(crate) fn do_completion_with_options(
    code: &str,
    kind: CompletionKind,
-    options: &CompletionOptions,
+    options: &CompletionConfig,
 ) -> Vec<CompletionItem> {
    let (analysis, position) = if code.contains("//-") {
        analysis_and_position(code)
diff --git a/crates/ra_ide/src/inlay_hints.rs b/crates/ra_ide/src/inlay_hints.rs
index f4f0751c0..d06fc03d3 100644
--- a/crates/ra_ide/src/inlay_hints.rs
+++ b/crates/ra_ide/src/inlay_hints.rs
@@ -11,14 +11,14 @@ use ra_syntax::{
 use crate::{FileId, FunctionSignature};
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub struct InlayHintsOptions {
+pub struct InlayHintsConfig {
    pub type_hints: bool,
    pub parameter_hints: bool,
    pub chaining_hints: bool,
    pub max_length: Option<usize>,
 }
-impl Default for InlayHintsOptions {
+impl Default for InlayHintsConfig {
    fn default() -> Self {
        Self { type_hints: true, parameter_hints: true, chaining_hints: true, max_length: None }
    }
@@ -41,7 +41,7 @@ pub struct InlayHint {
 pub(crate) fn inlay_hints(
    db: &RootDatabase,
    file_id: FileId,
-    options: &InlayHintsOptions,
+    config: &InlayHintsConfig,
 ) -> Vec<InlayHint> {
    let _p = profile("inlay_hints");
    let sema = Semantics::new(db);
@@ -50,14 +50,14 @@ pub(crate) fn inlay_hints(
    let mut res = Vec::new();
    for node in file.syntax().descendants() {
        if let Some(expr) = ast::Expr::cast(node.clone()) {
-            get_chaining_hints(&mut res, &sema, options, expr);
+            get_chaining_hints(&mut res, &sema, config, expr);
        }
        match_ast! {
            match node {
-                ast::CallExpr(it) => { get_param_name_hints(&mut res, &sema, options, ast::Expr::from(it)); },
+                ast::CallExpr(it) => { get_param_name_hints(&mut res, &sema, config, ast::Expr::from(it)); },
-                ast::MethodCallExpr(it) => { get_param_name_hints(&mut res, &sema, options, ast::Expr::from(it)); },
+                ast::MethodCallExpr(it) => { get_param_name_hints(&mut res, &sema, config, ast::Expr::from(it)); },
-                ast::BindPat(it) => { get_bind_pat_hints(&mut res, &sema, options, it); },
+                ast::BindPat(it) => { get_bind_pat_hints(&mut res, &sema, config, it); },
                _ => (),
            }
        }
@@ -68,10 +68,10 @@ pub(crate) fn inlay_hints(
 fn get_chaining_hints(
    acc: &mut Vec<InlayHint>,
    sema: &Semantics<RootDatabase>,
-    options: &InlayHintsOptions,
+    config: &InlayHintsConfig,
    expr: ast::Expr,
 ) -> Option<()> {
-    if !options.chaining_hints {
+    if !config.chaining_hints {
        return None;
    }
@@ -95,7 +95,7 @@ fn get_chaining_hints(
    let next = tokens.next()?.kind();
    let next_next = tokens.next()?.kind();
    if next == SyntaxKind::WHITESPACE && next_next == SyntaxKind::DOT {
-        let label = ty.display_truncated(sema.db, options.max_length).to_string();
+        let label = ty.display_truncated(sema.db, config.max_length).to_string();
        acc.push(InlayHint {
            range: expr.syntax().text_range(),
            kind: InlayKind::ChainingHint,
@@ -108,10 +108,10 @@ fn get_chaining_hints(
 fn get_param_name_hints(
    acc: &mut Vec<InlayHint>,
    sema: &Semantics<RootDatabase>,
-    options: &InlayHintsOptions,
+    config: &InlayHintsConfig,
    expr: ast::Expr,
 ) -> Option<()> {
-    if !options.parameter_hints {
+    if !config.parameter_hints {
        return None;
    }
@@ -148,10 +148,10 @@ fn get_param_name_hints(
 fn get_bind_pat_hints(
    acc: &mut Vec<InlayHint>,
    sema: &Semantics<RootDatabase>,
-    options: &InlayHintsOptions,
+    config: &InlayHintsConfig,
    pat: ast::BindPat,
 ) -> Option<()> {
-    if !options.type_hints {
+    if !config.type_hints {
        return None;
    }
@@ -164,7 +164,7 @@ fn get_bind_pat_hints(
    acc.push(InlayHint {
        range: pat.syntax().text_range(),
        kind: InlayKind::TypeHint,
-        label: ty.display_truncated(sema.db, options.max_length).to_string().into(),
+        label: ty.display_truncated(sema.db, config.max_length).to_string().into(),
    });
    Some(())
 }
@@ -270,7 +270,7 @@ fn get_fn_signature(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> Option<
 #[cfg(test)]
 mod tests {
-    use crate::inlay_hints::InlayHintsOptions;
+    use crate::inlay_hints::InlayHintsConfig;
    use insta::assert_debug_snapshot;
    use crate::mock_analysis::single_file;
@@ -284,7 +284,7 @@ mod tests {
                let _x = foo(4, 4);
            }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions{ parameter_hints: true, type_hints: false, chaining_hints: false, max_length: None}).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig{ parameter_hints: true, type_hints: false, chaining_hints: false, max_length: None}).unwrap(), @r###"
        [
            InlayHint {
                range: [106; 107),
@@ -308,7 +308,7 @@ mod tests {
                let _x = foo(4, 4);
            }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions{ type_hints: false, parameter_hints: false, chaining_hints: false, max_length: None}).unwrap(), @r###"[]"###);
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig{ type_hints: false, parameter_hints: false, chaining_hints: false, max_length: None}).unwrap(), @r###"[]"###);
    }
    #[test]
@@ -320,7 +320,7 @@ mod tests {
                let _x = foo(4, 4);
            }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions{ type_hints: true, parameter_hints: false, chaining_hints: false, max_length: None}).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig{ type_hints: true, parameter_hints: false, chaining_hints: false, max_length: None}).unwrap(), @r###"
        [
            InlayHint {
                range: [97; 99),
@@ -344,7 +344,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions::default()).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig::default()).unwrap(), @r###"
        [
            InlayHint {
                range: [69; 71),
@@ -401,7 +401,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions::default()).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig::default()).unwrap(), @r###"
        [
            InlayHint {
                range: [193; 197),
@@ -481,7 +481,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions::default()).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig::default()).unwrap(), @r###"
        [
            InlayHint {
                range: [21; 30),
@@ -545,7 +545,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions::default()).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig::default()).unwrap(), @r###"
        [
            InlayHint {
                range: [21; 30),
@@ -595,7 +595,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions::default()).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig::default()).unwrap(), @r###"
        [
            InlayHint {
                range: [188; 192),
@@ -690,7 +690,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions::default()).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig::default()).unwrap(), @r###"
        [
            InlayHint {
                range: [188; 192),
@@ -785,7 +785,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions::default()).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig::default()).unwrap(), @r###"
        [
            InlayHint {
                range: [252; 256),
@@ -857,7 +857,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions { max_length: Some(8), ..Default::default() }).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig { max_length: Some(8), ..Default::default() }).unwrap(), @r###"
        [
            InlayHint {
                range: [74; 75),
@@ -945,7 +945,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions::default()).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig::default()).unwrap(), @r###"
        [
            InlayHint {
                range: [798; 809),
@@ -1067,7 +1067,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions { max_length: Some(8), ..Default::default() }).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig { max_length: Some(8), ..Default::default() }).unwrap(), @r###"
        []
        "###
        );
@@ -1093,7 +1093,7 @@ fn main() {
 }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions { max_length: Some(8), ..Default::default() }).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig { max_length: Some(8), ..Default::default() }).unwrap(), @r###"
        []
        "###
        );
@@ -1115,7 +1115,7 @@ fn main() {
                    .into_c();
            }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions{ parameter_hints: false, type_hints: false, chaining_hints: true, max_length: None}).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig{ parameter_hints: false, type_hints: false, chaining_hints: true, max_length: None}).unwrap(), @r###"
        [
            InlayHint {
                range: [232; 269),
@@ -1144,7 +1144,7 @@ fn main() {
                let c = A(B(C)).into_b().into_c();
            }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions{ parameter_hints: false, type_hints: false, chaining_hints: true, max_length: None}).unwrap(), @r###"[]"###);
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig{ parameter_hints: false, type_hints: false, chaining_hints: true, max_length: None}).unwrap(), @r###"[]"###);
    }
    #[test]
@@ -1162,7 +1162,7 @@ fn main() {
                    .0;
            }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions{ parameter_hints: false, type_hints: false, chaining_hints: true, max_length: None}).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig{ parameter_hints: false, type_hints: false, chaining_hints: true, max_length: None}).unwrap(), @r###"
        [
            InlayHint {
                range: [150; 221),
@@ -1204,7 +1204,7 @@ fn main() {
                    .into_c();
            }"#,
        );
-        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsOptions{ parameter_hints: false, type_hints: false, chaining_hints: true, max_length: None}).unwrap(), @r###"
+        assert_debug_snapshot!(analysis.inlay_hints(file_id, &InlayHintsConfig{ parameter_hints: false, type_hints: false, chaining_hints: true, max_length: None}).unwrap(), @r###"
        [
            InlayHint {
                range: [403; 452),
diff --git a/crates/ra_ide/src/lib.rs b/crates/ra_ide/src/lib.rs
index 937c9caa5..285381086 100644
--- a/crates/ra_ide/src/lib.rs
+++ b/crates/ra_ide/src/lib.rs
@@ -62,13 +62,13 @@ use crate::display::ToNav;
 pub use crate::{
    assists::{Assist, AssistId},
    call_hierarchy::CallItem,
-    completion::{CompletionItem, CompletionItemKind, CompletionOptions, InsertTextFormat},
+    completion::{CompletionConfig, CompletionItem, CompletionItemKind, InsertTextFormat},
    diagnostics::Severity,
    display::{file_structure, FunctionSignature, NavigationTarget, StructureNode},
    expand_macro::ExpandedMacro,
    folding_ranges::{Fold, FoldKind},
    hover::HoverResult,
-    inlay_hints::{InlayHint, InlayHintsOptions, InlayKind},
+    inlay_hints::{InlayHint, InlayHintsConfig, InlayKind},
    references::{Declaration, Reference, ReferenceAccess, ReferenceKind, ReferenceSearchResult},
    runnables::{Runnable, RunnableKind, TestId},
    source_change::{FileSystemEdit, SourceChange, SourceFileEdit},
@@ -325,9 +325,9 @@ impl Analysis {
    pub fn inlay_hints(
        &self,
        file_id: FileId,
-        inlay_hint_opts: &InlayHintsOptions,
+        config: &InlayHintsConfig,
    ) -> Cancelable<Vec<InlayHint>> {
-        self.with_db(|db| inlay_hints::inlay_hints(db, file_id, inlay_hint_opts))
+        self.with_db(|db| inlay_hints::inlay_hints(db, file_id, config))
    }
    /// Returns the set of folding ranges.
@@ -450,9 +450,9 @@ impl Analysis {
    pub fn completions(
        &self,
        position: FilePosition,
-        options: &CompletionOptions,
+        config: &CompletionConfig,
    ) -> Cancelable<Option<Vec<CompletionItem>>> {
-        self.with_db(|db| completion::completions(db, position, options).map(Into::into))
+        self.with_db(|db| completion::completions(db, position, config).map(Into::into))
    }
    /// Computes assists (aka code actions aka intentions) for the given
diff --git a/crates/ra_proc_macro/Cargo.toml b/crates/ra_proc_macro/Cargo.toml
index bc2c37296..d009ceb82 100644
--- a/crates/ra_proc_macro/Cargo.toml
+++ b/crates/ra_proc_macro/Cargo.toml
@@ -10,3 +10,8 @@ doctest = false
 [dependencies]
 ra_tt = { path = "../ra_tt" }
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+log = "0.4.8"
+crossbeam-channel = "0.4.0"
+jod-thread = "0.1.1"
diff --git a/crates/ra_proc_macro/src/lib.rs b/crates/ra_proc_macro/src/lib.rs
index 5e21dd487..51fbb046a 100644
--- a/crates/ra_proc_macro/src/lib.rs
+++ b/crates/ra_proc_macro/src/lib.rs
@@ -5,55 +5,104 @@
 //! is used to provide basic infrastructure  for communication between two
 //! processes: Client (RA itself), Server (the external program)
+mod rpc;
+mod process;
+pub mod msg;
+use process::{ProcMacroProcessSrv, ProcMacroProcessThread};
 use ra_tt::{SmolStr, Subtree};
+use rpc::ProcMacroKind;
 use std::{
    path::{Path, PathBuf},
    sync::Arc,
 };
-#[derive(Debug, Clone, PartialEq, Eq)]
+pub use rpc::{ExpansionResult, ExpansionTask};
+#[derive(Debug, Clone)]
 pub struct ProcMacroProcessExpander {
    process: Arc<ProcMacroProcessSrv>,
+    dylib_path: PathBuf,
    name: SmolStr,
 }
+impl Eq for ProcMacroProcessExpander {}
+impl PartialEq for ProcMacroProcessExpander {
+    fn eq(&self, other: &Self) -> bool {
+        self.name == other.name
+            && self.dylib_path == other.dylib_path
+            && Arc::ptr_eq(&self.process, &other.process)
+    }
+}
 impl ra_tt::TokenExpander for ProcMacroProcessExpander {
    fn expand(
        &self,
-        _subtree: &Subtree,
+        subtree: &Subtree,
        _attr: Option<&Subtree>,
    ) -> Result<Subtree, ra_tt::ExpansionError> {
-        // FIXME: do nothing for now
+        self.process.custom_derive(&self.dylib_path, subtree, &self.name)
-        Ok(Subtree::default())
    }
 }
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug)]
-pub struct ProcMacroProcessSrv {
+enum ProcMacroClientKind {
-    path: PathBuf,
+    Process { process: Arc<ProcMacroProcessSrv>, thread: ProcMacroProcessThread },
+    Dummy,
 }
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug)]
-pub enum ProcMacroClient {
+pub struct ProcMacroClient {
-    Process { process: Arc<ProcMacroProcessSrv> },
+    kind: ProcMacroClientKind,
-    Dummy,
 }
 impl ProcMacroClient {
-    pub fn extern_process(process_path: &Path) -> ProcMacroClient {
+    pub fn extern_process(process_path: &Path) -> Result<ProcMacroClient, std::io::Error> {
-        let process = ProcMacroProcessSrv { path: process_path.into() };
+        let (thread, process) = ProcMacroProcessSrv::run(process_path)?;
-        ProcMacroClient::Process { process: Arc::new(process) }
+        Ok(ProcMacroClient {
+            kind: ProcMacroClientKind::Process { process: Arc::new(process), thread },
+        })
    }
    pub fn dummy() -> ProcMacroClient {
-        ProcMacroClient::Dummy
+        ProcMacroClient { kind: ProcMacroClientKind::Dummy }
    }
    pub fn by_dylib_path(
        &self,
-        _dylib_path: &Path,
+        dylib_path: &Path,
    ) -> Vec<(SmolStr, Arc<dyn ra_tt::TokenExpander>)> {
-        // FIXME: return empty for now
+        match &self.kind {
-        vec![]
+            ProcMacroClientKind::Dummy => vec![],
+            ProcMacroClientKind::Process { process, .. } => {
+                let macros = match process.find_proc_macros(dylib_path) {
+                    Err(err) => {
+                        eprintln!("Fail to find proc macro. Error: {:#?}", err);
+                        return vec![];
+                    }
+                    Ok(macros) => macros,
+                };
+                macros
+                    .into_iter()
+                    .filter_map(|(name, kind)| {
+                        // FIXME: Support custom derive only for now.
+                        match kind {
+                            ProcMacroKind::CustomDerive => {
+                                let name = SmolStr::new(&name);
+                                let expander: Arc<dyn ra_tt::TokenExpander> =
+                                    Arc::new(ProcMacroProcessExpander {
+                                        process: process.clone(),
+                                        name: name.clone(),
+                                        dylib_path: dylib_path.into(),
+                                    });
+                                Some((name, expander))
+                            }
+                            _ => None,
+                        }
+                    })
+                    .collect()
+            }
+        }
    }
 }
diff --git a/crates/ra_proc_macro/src/msg.rs b/crates/ra_proc_macro/src/msg.rs
new file mode 100644
index 000000000..aa95bcc8f
--- /dev/null
+++ b/crates/ra_proc_macro/src/msg.rs
@@ -0,0 +1,93 @@
+//! Defines messages for cross-process message based on `ndjson` wire protocol
+use std::{
+    convert::TryFrom,
+    io::{self, BufRead, Write},
+};
+use crate::{
+    rpc::{ListMacrosResult, ListMacrosTask},
+    ExpansionResult, ExpansionTask,
+};
+use serde::{de::DeserializeOwned, Deserialize, Serialize};
+#[derive(Debug, Serialize, Deserialize, Clone)]
+pub enum Request {
+    ListMacro(ListMacrosTask),
+    ExpansionMacro(ExpansionTask),
+}
+#[derive(Debug, Serialize, Deserialize, Clone)]
+pub enum Response {
+    Error(ResponseError),
+    ListMacro(ListMacrosResult),
+    ExpansionMacro(ExpansionResult),
+}
+macro_rules! impl_try_from_response {
+    ($ty:ty, $tag:ident) => {
+        impl TryFrom<Response> for $ty {
+            type Error = &'static str;
+            fn try_from(value: Response) -> Result<Self, Self::Error> {
+                match value {
+                    Response::$tag(res) => Ok(res),
+                    _ => Err("Fail to convert from response"),
+                }
+            }
+        }
+    };
+}
+impl_try_from_response!(ListMacrosResult, ListMacro);
+impl_try_from_response!(ExpansionResult, ExpansionMacro);
+#[derive(Debug, Serialize, Deserialize, Clone)]
+pub struct ResponseError {
+    pub code: ErrorCode,
+    pub message: String,
+}
+#[derive(Debug, Serialize, Deserialize, Clone)]
+pub enum ErrorCode {
+    ServerErrorEnd,
+    ExpansionError,
+}
+pub trait Message: Sized + Serialize + DeserializeOwned {
+    fn read(r: &mut impl BufRead) -> io::Result<Option<Self>> {
+        let text = match read_json(r)? {
+            None => return Ok(None),
+            Some(text) => text,
+        };
+        let msg = serde_json::from_str(&text)?;
+        Ok(Some(msg))
+    }
+    fn write(self, w: &mut impl Write) -> io::Result<()> {
+        let text = serde_json::to_string(&self)?;
+        write_json(w, &text)
+    }
+}
+impl Message for Request {}
+impl Message for Response {}
+fn read_json(inp: &mut impl BufRead) -> io::Result<Option<String>> {
+    let mut buf = String::new();
+    if inp.read_line(&mut buf)? == 0 {
+        return Ok(None);
+    }
+    // Remove ending '\n'
+    let buf = &buf[..buf.len() - 1];
+    if buf.is_empty() {
+        return Ok(None);
+    }
+    Ok(Some(buf.to_string()))
+}
+fn write_json(out: &mut impl Write, msg: &str) -> io::Result<()> {
+    log::debug!("> {}", msg);
+    out.write_all(msg.as_bytes())?;
+    out.write_all(b"\n")?;
+    out.flush()?;
+    Ok(())
+}
diff --git a/crates/ra_proc_macro/src/process.rs b/crates/ra_proc_macro/src/process.rs
new file mode 100644
index 000000000..e8c85be38
--- /dev/null
+++ b/crates/ra_proc_macro/src/process.rs
@@ -0,0 +1,196 @@
+//! Handle process life-time and message passing for proc-macro client
+use crossbeam_channel::{bounded, Receiver, Sender};
+use ra_tt::Subtree;
+use crate::msg::{ErrorCode, Message, Request, Response, ResponseError};
+use crate::rpc::{ExpansionResult, ExpansionTask, ListMacrosResult, ListMacrosTask, ProcMacroKind};
+use io::{BufRead, BufReader};
+use std::{
+    convert::{TryFrom, TryInto},
+    io::{self, Write},
+    path::{Path, PathBuf},
+    process::{Child, Command, Stdio},
+    sync::{Arc, Weak},
+};
+#[derive(Debug, Default)]
+pub(crate) struct ProcMacroProcessSrv {
+    inner: Option<Weak<Sender<Task>>>,
+}
+#[derive(Debug)]
+pub(crate) struct ProcMacroProcessThread {
+    // XXX: drop order is significant
+    sender: Arc<Sender<Task>>,
+    handle: jod_thread::JoinHandle<()>,
+}
+struct Task {
+    req: Request,
+    result_tx: Sender<Option<Response>>,
+}
+struct Process {
+    path: PathBuf,
+    child: Child,
+}
+impl Drop for Process {
+    fn drop(&mut self) {
+        let _ = self.child.kill();
+    }
+}
+impl Process {
+    fn run(process_path: &Path) -> Result<Process, io::Error> {
+        let child = Command::new(process_path.clone())
+            .stdin(Stdio::piped())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::null())
+            .spawn()?;
+        Ok(Process { path: process_path.into(), child })
+    }
+    fn restart(&mut self) -> Result<(), io::Error> {
+        let _ = self.child.kill();
+        self.child = Command::new(self.path.clone())
+            .stdin(Stdio::piped())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::null())
+            .spawn()?;
+        Ok(())
+    }
+    fn stdio(&mut self) -> Option<(impl Write, impl BufRead)> {
+        let stdin = self.child.stdin.take()?;
+        let stdout = self.child.stdout.take()?;
+        let read = BufReader::new(stdout);
+        Some((stdin, read))
+    }
+}
+impl ProcMacroProcessSrv {
+    pub fn run(
+        process_path: &Path,
+    ) -> Result<(ProcMacroProcessThread, ProcMacroProcessSrv), io::Error> {
+        let process = Process::run(process_path)?;
+        let (task_tx, task_rx) = bounded(0);
+        let handle = jod_thread::spawn(move || {
+            client_loop(task_rx, process);
+        });
+        let task_tx = Arc::new(task_tx);
+        let srv = ProcMacroProcessSrv { inner: Some(Arc::downgrade(&task_tx)) };
+        let thread = ProcMacroProcessThread { handle, sender: task_tx };
+        Ok((thread, srv))
+    }
+    pub fn find_proc_macros(
+        &self,
+        dylib_path: &Path,
+    ) -> Result<Vec<(String, ProcMacroKind)>, ra_tt::ExpansionError> {
+        let task = ListMacrosTask { lib: dylib_path.to_path_buf() };
+        let result: ListMacrosResult = self.send_task(Request::ListMacro(task))?;
+        Ok(result.macros)
+    }
+    pub fn custom_derive(
+        &self,
+        dylib_path: &Path,
+        subtree: &Subtree,
+        derive_name: &str,
+    ) -> Result<Subtree, ra_tt::ExpansionError> {
+        let task = ExpansionTask {
+            macro_body: subtree.clone(),
+            macro_name: derive_name.to_string(),
+            attributes: None,
+            lib: dylib_path.to_path_buf(),
+        };
+        let result: ExpansionResult = self.send_task(Request::ExpansionMacro(task))?;
+        Ok(result.expansion)
+    }
+    pub fn send_task<R>(&self, req: Request) -> Result<R, ra_tt::ExpansionError>
+    where
+        R: TryFrom<Response, Error = &'static str>,
+    {
+        let sender = match &self.inner {
+            None => return Err(ra_tt::ExpansionError::Unknown("No sender is found.".to_string())),
+            Some(it) => it,
+        };
+        let (result_tx, result_rx) = bounded(0);
+        let sender = match sender.upgrade() {
+            None => {
+                return Err(ra_tt::ExpansionError::Unknown("Proc macro process is closed.".into()))
+            }
+            Some(it) => it,
+        };
+        sender.send(Task { req: req.into(), result_tx }).unwrap();
+        let res = result_rx
+            .recv()
+            .map_err(|_| ra_tt::ExpansionError::Unknown("Proc macro thread is closed.".into()))?;
+        match res {
+            Some(Response::Error(err)) => {
+                return Err(ra_tt::ExpansionError::ExpansionError(err.message));
+            }
+            Some(res) => Ok(res.try_into().map_err(|err| {
+                ra_tt::ExpansionError::Unknown(format!(
+                    "Fail to get response, reason : {:#?} ",
+                    err
+                ))
+            })?),
+            None => Err(ra_tt::ExpansionError::Unknown("Empty result".into())),
+        }
+    }
+}
+fn client_loop(task_rx: Receiver<Task>, mut process: Process) {
+    let (mut stdin, mut stdout) = match process.stdio() {
+        None => return,
+        Some(it) => it,
+    };
+    for task in task_rx {
+        let Task { req, result_tx } = task;
+        match send_request(&mut stdin, &mut stdout, req) {
+            Ok(res) => result_tx.send(res).unwrap(),
+            Err(_err) => {
+                let res = Response::Error(ResponseError {
+                    code: ErrorCode::ServerErrorEnd,
+                    message: "Server closed".into(),
+                });
+                result_tx.send(res.into()).unwrap();
+                // Restart the process
+                if process.restart().is_err() {
+                    break;
+                }
+                let stdio = match process.stdio() {
+                    None => break,
+                    Some(it) => it,
+                };
+                stdin = stdio.0;
+                stdout = stdio.1;
+            }
+        }
+    }
+}
+fn send_request(
+    mut writer: &mut impl Write,
+    mut reader: &mut impl BufRead,
+    req: Request,
+) -> Result<Option<Response>, io::Error> {
+    req.write(&mut writer)?;
+    Ok(Response::read(&mut reader)?)
+}
diff --git a/crates/ra_proc_macro/src/rpc.rs b/crates/ra_proc_macro/src/rpc.rs
new file mode 100644
index 000000000..66b3f55db
--- /dev/null
+++ b/crates/ra_proc_macro/src/rpc.rs
@@ -0,0 +1,266 @@
+//! Data struture serialization related stuffs for RPC
+//!
+//! Define all necessary rpc serialization data structure,
+//! which include ra_tt related data and some task messages.
+//! Although adding Serialize and Deserialize trait to ra_tt directly seem to be much easier,
+//! we deliberately duplicate the ra_tt struct with #[serde(with = "XXDef")]
+//! for separation of code responsibility.
+use ra_tt::{
+    Delimiter, DelimiterKind, Ident, Leaf, Literal, Punct, SmolStr, Spacing, Subtree, TokenId,
+    TokenTree,
+};
+use serde::{Deserialize, Serialize};
+use std::path::PathBuf;
+#[derive(Clone, Eq, PartialEq, Debug, Serialize, Deserialize)]
+pub struct ListMacrosTask {
+    pub lib: PathBuf,
+}
+#[derive(Clone, Eq, PartialEq, Debug, Serialize, Deserialize)]
+pub enum ProcMacroKind {
+    CustomDerive,
+    FuncLike,
+    Attr,
+}
+#[derive(Clone, Eq, PartialEq, Debug, Default, Serialize, Deserialize)]
+pub struct ListMacrosResult {
+    pub macros: Vec<(String, ProcMacroKind)>,
+}
+#[derive(Clone, Eq, PartialEq, Debug, Serialize, Deserialize)]
+pub struct ExpansionTask {
+    /// Argument of macro call.
+    ///
+    /// In custom derive that would be a struct or enum; in attribute-like macro - underlying
+    /// item; in function-like macro - the macro body.
+    #[serde(with = "SubtreeDef")]
+    pub macro_body: Subtree,
+    /// Names of macros to expand.
+    ///
+    /// In custom derive those are names of derived traits (`Serialize`, `Getters`, etc.). In
+    /// attribute-like and functiona-like macros - single name of macro itself (`show_streams`).
+    pub macro_name: String,
+    /// Possible attributes for the attribute-like macros.
+    #[serde(with = "opt_subtree_def")]
+    pub attributes: Option<Subtree>,
+    pub lib: PathBuf,
+}
+#[derive(Clone, Eq, PartialEq, Debug, Default, Serialize, Deserialize)]
+pub struct ExpansionResult {
+    #[serde(with = "SubtreeDef")]
+    pub expansion: Subtree,
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "DelimiterKind")]
+enum DelimiterKindDef {
+    Parenthesis,
+    Brace,
+    Bracket,
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "TokenId")]
+struct TokenIdDef(u32);
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "Delimiter")]
+struct DelimiterDef {
+    #[serde(with = "TokenIdDef")]
+    pub id: TokenId,
+    #[serde(with = "DelimiterKindDef")]
+    pub kind: DelimiterKind,
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "Subtree")]
+struct SubtreeDef {
+    #[serde(default, with = "opt_delimiter_def")]
+    pub delimiter: Option<Delimiter>,
+    #[serde(with = "vec_token_tree")]
+    pub token_trees: Vec<TokenTree>,
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "TokenTree")]
+enum TokenTreeDef {
+    #[serde(with = "LeafDef")]
+    Leaf(Leaf),
+    #[serde(with = "SubtreeDef")]
+    Subtree(Subtree),
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "Leaf")]
+enum LeafDef {
+    #[serde(with = "LiteralDef")]
+    Literal(Literal),
+    #[serde(with = "PunctDef")]
+    Punct(Punct),
+    #[serde(with = "IdentDef")]
+    Ident(Ident),
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "Literal")]
+struct LiteralDef {
+    pub text: SmolStr,
+    #[serde(with = "TokenIdDef")]
+    pub id: TokenId,
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "Punct")]
+struct PunctDef {
+    pub char: char,
+    #[serde(with = "SpacingDef")]
+    pub spacing: Spacing,
+    #[serde(with = "TokenIdDef")]
+    pub id: TokenId,
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "Spacing")]
+enum SpacingDef {
+    Alone,
+    Joint,
+}
+#[derive(Serialize, Deserialize)]
+#[serde(remote = "Ident")]
+struct IdentDef {
+    pub text: SmolStr,
+    #[serde(with = "TokenIdDef")]
+    pub id: TokenId,
+}
+mod opt_delimiter_def {
+    use super::{Delimiter, DelimiterDef};
+    use serde::{Deserialize, Deserializer, Serialize, Serializer};
+    pub fn serialize<S>(value: &Option<Delimiter>, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        #[derive(Serialize)]
+        struct Helper<'a>(#[serde(with = "DelimiterDef")] &'a Delimiter);
+        value.as_ref().map(Helper).serialize(serializer)
+    }
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<Option<Delimiter>, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        #[derive(Deserialize)]
+        struct Helper(#[serde(with = "DelimiterDef")] Delimiter);
+        let helper = Option::deserialize(deserializer)?;
+        Ok(helper.map(|Helper(external)| external))
+    }
+}
+mod opt_subtree_def {
+    use super::{Subtree, SubtreeDef};
+    use serde::{Deserialize, Deserializer, Serialize, Serializer};
+    pub fn serialize<S>(value: &Option<Subtree>, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        #[derive(Serialize)]
+        struct Helper<'a>(#[serde(with = "SubtreeDef")] &'a Subtree);
+        value.as_ref().map(Helper).serialize(serializer)
+    }
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<Option<Subtree>, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        #[derive(Deserialize)]
+        struct Helper(#[serde(with = "SubtreeDef")] Subtree);
+        let helper = Option::deserialize(deserializer)?;
+        Ok(helper.map(|Helper(external)| external))
+    }
+}
+mod vec_token_tree {
+    use super::{TokenTree, TokenTreeDef};
+    use serde::{ser::SerializeSeq, Deserialize, Deserializer, Serialize, Serializer};
+    pub fn serialize<S>(value: &Vec<TokenTree>, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        #[derive(Serialize)]
+        struct Helper<'a>(#[serde(with = "TokenTreeDef")] &'a TokenTree);
+        let items: Vec<_> = value.iter().map(Helper).collect();
+        let mut seq = serializer.serialize_seq(Some(items.len()))?;
+        for element in items {
+            seq.serialize_element(&element)?;
+        }
+        seq.end()
+    }
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<Vec<TokenTree>, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        #[derive(Deserialize)]
+        struct Helper(#[serde(with = "TokenTreeDef")] TokenTree);
+        let helper = Vec::deserialize(deserializer)?;
+        Ok(helper.into_iter().map(|Helper(external)| external).collect())
+    }
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    fn fixture_token_tree() -> Subtree {
+        let mut subtree = Subtree::default();
+        subtree
+            .token_trees
+            .push(TokenTree::Leaf(Ident { text: "struct".into(), id: TokenId(0) }.into()));
+        subtree
+            .token_trees
+            .push(TokenTree::Leaf(Ident { text: "Foo".into(), id: TokenId(1) }.into()));
+        subtree.token_trees.push(TokenTree::Subtree(
+            Subtree {
+                delimiter: Some(Delimiter { id: TokenId(2), kind: DelimiterKind::Brace }),
+                token_trees: vec![],
+            }
+            .into(),
+        ));
+        subtree
+    }
+    #[test]
+    fn test_proc_macro_rpc_works() {
+        let tt = fixture_token_tree();
+        let task = ExpansionTask {
+            macro_body: tt.clone(),
+            macro_name: Default::default(),
+            attributes: None,
+            lib: Default::default(),
+        };
+        let json = serde_json::to_string(&task).unwrap();
+        let back: ExpansionTask = serde_json::from_str(&json).unwrap();
+        assert_eq!(task.macro_body, back.macro_body);
+        let result = ExpansionResult { expansion: tt.clone() };
+        let json = serde_json::to_string(&result).unwrap();
+        let back: ExpansionResult = serde_json::from_str(&json).unwrap();
+        assert_eq!(result, back);
+    }
+}
diff --git a/crates/ra_project_model/Cargo.toml b/crates/ra_project_model/Cargo.toml
index cdcdd63c9..b10644b4b 100644
--- a/crates/ra_project_model/Cargo.toml
+++ b/crates/ra_project_model/Cargo.toml
@@ -16,7 +16,6 @@ cargo_metadata = "0.9.1"
 ra_arena = { path = "../ra_arena" }
 ra_db = { path = "../ra_db" }
 ra_cfg = { path = "../ra_cfg" }
-ra_cargo_watch = { path = "../ra_cargo_watch" }
 ra_proc_macro =  { path = "../ra_proc_macro" }
 serde = { version = "1.0.104", features = ["derive"] }
diff --git a/crates/ra_project_model/src/cargo_workspace.rs b/crates/ra_project_model/src/cargo_workspace.rs
index 291594e2a..f4fd6ad28 100644
--- a/crates/ra_project_model/src/cargo_workspace.rs
+++ b/crates/ra_project_model/src/cargo_workspace.rs
@@ -1,14 +1,16 @@
 //! FIXME: write short doc here
 use std::{
+    env,
+    ffi::OsStr,
    ops,
    path::{Path, PathBuf},
+    process::Command,
 };
 use anyhow::{Context, Result};
 use cargo_metadata::{BuildScript, CargoOpt, Message, MetadataCommand, PackageId};
 use ra_arena::{Arena, Idx};
-use ra_cargo_watch::run_cargo;
 use ra_db::Edition;
 use rustc_hash::FxHashMap;
 use serde::Deserialize;
@@ -75,6 +77,7 @@ pub type Target = Idx<TargetData>;
 #[derive(Debug, Clone)]
 pub struct PackageData {
+    pub id: String,
    pub name: String,
    pub manifest: PathBuf,
    pub targets: Vec<Target>,
@@ -161,7 +164,7 @@ impl CargoWorkspace {
        let mut out_dir_by_id = FxHashMap::default();
        let mut proc_macro_dylib_paths = FxHashMap::default();
        if cargo_features.load_out_dirs_from_check {
-            let resources = load_extern_resources(cargo_toml, cargo_features);
+            let resources = load_extern_resources(cargo_toml, cargo_features)?;
            out_dir_by_id = resources.out_dirs;
            proc_macro_dylib_paths = resources.proc_dylib_paths;
        }
@@ -180,6 +183,7 @@ impl CargoWorkspace {
                .with_context(|| format!("Failed to parse edition {}", edition))?;
            let pkg = packages.alloc(PackageData {
                name,
+                id: id.to_string(),
                manifest: manifest_path,
                targets: Vec::new(),
                is_member,
@@ -249,6 +253,18 @@ impl CargoWorkspace {
    pub fn workspace_root(&self) -> &Path {
        &self.workspace_root
    }
+    pub fn package_flag(&self, package: &PackageData) -> String {
+        if self.is_unique(&*package.name) {
+            package.name.clone()
+        } else {
+            package.id.clone()
+        }
+    }
+    fn is_unique(&self, name: &str) -> bool {
+        self.packages.iter().filter(|(_, v)| v.name == name).count() == 1
+    }
 }
 #[derive(Debug, Clone, Default)]
@@ -257,48 +273,61 @@ pub struct ExternResources {
    proc_dylib_paths: FxHashMap<PackageId, PathBuf>,
 }
-pub fn load_extern_resources(cargo_toml: &Path, cargo_features: &CargoFeatures) -> ExternResources {
+pub fn load_extern_resources(
-    let mut args: Vec<String> = vec![
+    cargo_toml: &Path,
-        "check".to_string(),
+    cargo_features: &CargoFeatures,
-        "--message-format=json".to_string(),
+) -> Result<ExternResources> {
-        "--manifest-path".to_string(),
+    let mut cmd = Command::new(cargo_binary());
-        cargo_toml.display().to_string(),
+    cmd.args(&["check", "--message-format=json", "--manifest-path"]).arg(cargo_toml);
-    ];
    if cargo_features.all_features {
-        args.push("--all-features".to_string());
+        cmd.arg("--all-features");
    } else if cargo_features.no_default_features {
        // FIXME: `NoDefaultFeatures` is mutual exclusive with `SomeFeatures`
        // https://github.com/oli-obk/cargo_metadata/issues/79
-        args.push("--no-default-features".to_string());
+        cmd.arg("--no-default-features");
    } else {
-        args.extend(cargo_features.features.iter().cloned());
+        cmd.args(&cargo_features.features);
    }
-    let mut acc = ExternResources::default();
+    let output = cmd.output()?;
-    let res = run_cargo(&args, cargo_toml.parent(), &mut |message| {
-        match message {
-            Message::BuildScriptExecuted(BuildScript { package_id, out_dir, .. }) => {
-                acc.out_dirs.insert(package_id, out_dir);
-            }
-            Message::CompilerArtifact(message) => {
+    let mut res = ExternResources::default();
-                if message.target.kind.contains(&"proc-macro".to_string()) {
-                    let package_id = message.package_id;
+    let stdout = String::from_utf8(output.stdout)?;
-                    if let Some(filename) = message.filenames.get(0) {
+    for line in stdout.lines() {
-                        acc.proc_dylib_paths.insert(package_id, filename.clone());
+        if let Ok(message) = serde_json::from_str::<cargo_metadata::Message>(&line) {
+            match message {
+                Message::BuildScriptExecuted(BuildScript { package_id, out_dir, .. }) => {
+                    res.out_dirs.insert(package_id, out_dir);
+                }
+                Message::CompilerArtifact(message) => {
+                    if message.target.kind.contains(&"proc-macro".to_string()) {
+                        let package_id = message.package_id;
+                        // Skip rmeta file
+                        if let Some(filename) =
+                            message.filenames.iter().filter(|name| is_dylib(name)).next()
+                        {
+                            res.proc_dylib_paths.insert(package_id, filename.clone());
+                        }
                    }
                }
+                Message::CompilerMessage(_) => (),
+                Message::Unknown => (),
            }
-            Message::CompilerMessage(_) => (),
-            Message::Unknown => (),
        }
-        true
+    }
-    });
+    Ok(res)
+}
-    if let Err(err) = res {
+// FIXME: File a better way to know if it is a dylib
-        log::error!("Failed to load outdirs: {:?}", err);
+fn is_dylib(path: &Path) -> bool {
+    match path.extension().and_then(OsStr::to_str).map(|it| it.to_string().to_lowercase()) {
+        None => false,
+        Some(ext) => matches!(ext.as_str(), "dll" | "dylib" | "so"),
    }
+}
-    acc
+fn cargo_binary() -> String {
+    env::var("CARGO").unwrap_or_else(|_| "cargo".to_string())
 }
diff --git a/crates/ra_syntax/src/ast/edit.rs b/crates/ra_syntax/src/ast/edit.rs
index 3d023f189..b69cae234 100644
--- a/crates/ra_syntax/src/ast/edit.rs
+++ b/crates/ra_syntax/src/ast/edit.rs
@@ -369,22 +369,33 @@ impl ast::MatchArmList {
    #[must_use]
    pub fn remove_placeholder(&self) -> ast::MatchArmList {
-        let placeholder = self.arms().find(|arm| {
+        let placeholder =
-            if let Some(ast::Pat::PlaceholderPat(_)) = arm.pat() {
+            self.arms().find(|arm| matches!(arm.pat(), Some(ast::Pat::PlaceholderPat(_))));
-                return true;
-            }
-            false
-        });
        if let Some(placeholder) = placeholder {
-            let s: SyntaxElement = placeholder.syntax().clone().into();
+            self.remove_arm(&placeholder)
-            let e = s.clone();
-            self.replace_children(s..=e, &mut iter::empty())
        } else {
            self.clone()
        }
    }
    #[must_use]
+    fn remove_arm(&self, arm: &ast::MatchArm) -> ast::MatchArmList {
+        let start = arm.syntax().clone();
+        let end = if let Some(comma) = start
+            .siblings_with_tokens(Direction::Next)
+            .skip(1)
+            .skip_while(|it| it.kind().is_trivia())
+            .next()
+            .filter(|it| it.kind() == T![,])
+        {
+            comma
+        } else {
+            start.clone().into()
+        };
+        self.replace_children(start.into()..=end, None)
+    }
+    #[must_use]
    pub fn append_arm(&self, item: ast::MatchArm) -> ast::MatchArmList {
        let r_curly = match self.syntax().children_with_tokens().find(|it| it.kind() == T!['}']) {
            Some(t) => t,
diff --git a/crates/ra_syntax/src/parsing/text_tree_sink.rs b/crates/ra_syntax/src/parsing/text_tree_sink.rs
index dd202601d..87bb21cd9 100644
--- a/crates/ra_syntax/src/parsing/text_tree_sink.rs
+++ b/crates/ra_syntax/src/parsing/text_tree_sink.rs
@@ -149,10 +149,21 @@ fn n_attached_trivias<'a>(
        MACRO_CALL | CONST_DEF | TYPE_ALIAS_DEF | STRUCT_DEF | ENUM_DEF | ENUM_VARIANT | FN_DEF
        | TRAIT_DEF | MODULE | RECORD_FIELD_DEF | STATIC_DEF => {
            let mut res = 0;
-            for (i, (kind, text)) in trivias.enumerate() {
+            let mut trivias = trivias.enumerate().peekable();
+            while let Some((i, (kind, text))) = trivias.next() {
                match kind {
                    WHITESPACE => {
                        if text.contains("\n\n") {
+                            // we check whether the next token is a doc-comment
+                            // and skip the whitespace in this case
+                            if let Some((peek_kind, peek_text)) =
+                                trivias.peek().map(|(_, pair)| pair)
+                            {
+                                if *peek_kind == COMMENT && peek_text.starts_with("///") {
+                                    continue;
+                                }
+                            }
                            break;
                        }
                    }
diff --git a/crates/ra_syntax/test_data/parser/ok/0065_comment_newline.rs b/crates/ra_syntax/test_data/parser/ok/0065_comment_newline.rs
new file mode 100644
index 000000000..1fafe216b
--- /dev/null
+++ b/crates/ra_syntax/test_data/parser/ok/0065_comment_newline.rs
@@ -0,0 +1,3 @@
+/// Example
+fn test() {}
diff --git a/crates/ra_syntax/test_data/parser/ok/0065_comment_newline.txt b/crates/ra_syntax/test_data/parser/ok/0065_comment_newline.txt
new file mode 100644
index 000000000..91d0c3736
--- /dev/null
+++ b/crates/ra_syntax/test_data/parser/ok/0065_comment_newline.txt
@@ -0,0 +1,17 @@
+SOURCE_FILE@[0; 26)
+  FN_DEF@[0; 25)
+    COMMENT@[0; 11) "/// Example"
+    WHITESPACE@[11; 13) "\n\n"
+    FN_KW@[13; 15) "fn"
+    WHITESPACE@[15; 16) " "
+    NAME@[16; 20)
+      IDENT@[16; 20) "test"
+    PARAM_LIST@[20; 22)
+      L_PAREN@[20; 21) "("
+      R_PAREN@[21; 22) ")"
+    WHITESPACE@[22; 23) " "
+    BLOCK_EXPR@[23; 25)
+      BLOCK@[23; 25)
+        L_CURLY@[23; 24) "{"
+        R_CURLY@[24; 25) "}"
+  WHITESPACE@[25; 26) "\n"
diff --git a/crates/ra_tt/src/lib.rs b/crates/ra_tt/src/lib.rs
index 1015ce0a6..bd484aa30 100644
--- a/crates/ra_tt/src/lib.rs
+++ b/crates/ra_tt/src/lib.rs
@@ -189,7 +189,12 @@ impl Subtree {
 pub mod buffer;
 #[derive(Debug, PartialEq, Eq)]
-pub enum ExpansionError {}
+pub enum ExpansionError {
+    IOError(String),
+    JsonError(String),
+    Unknown(String),
+    ExpansionError(String),
+}
 pub trait TokenExpander: Debug + Send + Sync + RefUnwindSafe {
    fn expand(&self, subtree: &Subtree, attrs: Option<&Subtree>)
diff --git a/crates/rust-analyzer/Cargo.toml b/crates/rust-analyzer/Cargo.toml
index 8fe6799d2..f5f773432 100644
--- a/crates/rust-analyzer/Cargo.toml
+++ b/crates/rust-analyzer/Cargo.toml
@@ -33,7 +33,7 @@ threadpool = "1.7.1"
 stdx = { path = "../stdx" }
 lsp-server = "0.3.1"
-ra_cargo_watch = { path = "../ra_cargo_watch" }
+ra_flycheck = { path = "../ra_flycheck" }
 ra_ide = { path = "../ra_ide" }
 ra_prof = { path = "../ra_prof" }
 ra_project_model = { path = "../ra_project_model" }
diff --git a/crates/rust-analyzer/src/cargo_target_spec.rs b/crates/rust-analyzer/src/cargo_target_spec.rs
index f87bdcec5..942c30328 100644
--- a/crates/rust-analyzer/src/cargo_target_spec.rs
+++ b/crates/rust-analyzer/src/cargo_target_spec.rs
@@ -77,7 +77,7 @@ impl CargoTargetSpec {
            ProjectWorkspace::Cargo { cargo, .. } => {
                let tgt = cargo.target_by_root(&path)?;
                Some(CargoTargetSpec {
-                    package: cargo[cargo[tgt].package].name.clone(),
+                    package: cargo.package_flag(&cargo[cargo[tgt].package]),
                    target: cargo[tgt].name.clone(),
                    target_kind: cargo[tgt].kind,
                })
diff --git a/crates/rust-analyzer/src/cli/analysis_bench.rs b/crates/rust-analyzer/src/cli/analysis_bench.rs
index 7164b0ade..7667873d5 100644
--- a/crates/rust-analyzer/src/cli/analysis_bench.rs
+++ b/crates/rust-analyzer/src/cli/analysis_bench.rs
@@ -12,7 +12,7 @@ use ra_db::{
    salsa::{Database, Durability},
    FileId, SourceDatabaseExt,
 };
-use ra_ide::{Analysis, AnalysisChange, AnalysisHost, CompletionOptions, FilePosition, LineCol};
+use ra_ide::{Analysis, AnalysisChange, AnalysisHost, CompletionConfig, FilePosition, LineCol};
 use crate::cli::{load_cargo::load_cargo, Verbosity};
@@ -102,7 +102,7 @@ pub fn analysis_bench(
            let file_position = FilePosition { file_id, offset };
            if is_completion {
-                let options = CompletionOptions::default();
+                let options = CompletionConfig::default();
                let res = do_work(&mut host, file_id, |analysis| {
                    analysis.completions(file_position, &options)
                });
diff --git a/crates/rust-analyzer/src/conv.rs b/crates/rust-analyzer/src/conv.rs
index 6edc03fe0..e8dc953c3 100644
--- a/crates/rust-analyzer/src/conv.rs
+++ b/crates/rust-analyzer/src/conv.rs
@@ -579,7 +579,7 @@ impl TryConvWith<&WorldSnapshot> for (FileId, RangeInfo<Vec<NavigationTarget>>)
            .into_iter()
            .map(|nav| (file_id, RangeInfo::new(range, nav)))
            .try_conv_with_to_vec(world)?;
-        if world.options.supports_location_link {
+        if world.config.supports_location_link {
            Ok(links.into())
        } else {
            let locations: Vec<Location> = links
diff --git a/crates/rust-analyzer/src/main_loop.rs b/crates/rust-analyzer/src/main_loop.rs
index 79ea90cc9..bb33fb27d 100644
--- a/crates/rust-analyzer/src/main_loop.rs
+++ b/crates/rust-analyzer/src/main_loop.rs
@@ -21,8 +21,8 @@ use lsp_types::{
    WorkDoneProgressBegin, WorkDoneProgressCreateParams, WorkDoneProgressEnd,
    WorkDoneProgressReport,
 };
-use ra_cargo_watch::{url_from_path_with_drive_lowercasing, CheckOptions, CheckTask};
+use ra_flycheck::{url_from_path_with_drive_lowercasing, CheckConfig, CheckTask};
-use ra_ide::{Canceled, FileId, InlayHintsOptions, LibraryData, SourceRootId};
+use ra_ide::{Canceled, FileId, InlayHintsConfig, LibraryData, SourceRootId};
 use ra_prof::profile;
 use ra_vfs::{VfsFile, VfsTask, Watch};
 use relative_path::RelativePathBuf;
@@ -38,7 +38,7 @@ use crate::{
        subscriptions::Subscriptions,
    },
    req,
-    world::{Options, WorldSnapshot, WorldState},
+    world::{Config, WorldSnapshot, WorldState},
    Result, ServerConfig,
 };
 use req::ConfigurationParams;
@@ -81,11 +81,11 @@ fn get_feature_flags(config: &ServerConfig, connection: &Connection) -> FeatureF
    ff
 }
-fn get_options(
+fn get_config(
    config: &ServerConfig,
    text_document_caps: Option<&TextDocumentClientCapabilities>,
-) -> Options {
+) -> Config {
-    Options {
+    Config {
        publish_decorations: config.publish_decorations,
        supports_location_link: text_document_caps
            .and_then(|it| it.definition)
@@ -95,13 +95,13 @@ fn get_options(
            .and_then(|it| it.folding_range.as_ref())
            .and_then(|it| it.line_folding_only)
            .unwrap_or(false),
-        inlay_hints: InlayHintsOptions {
+        inlay_hints: InlayHintsConfig {
            type_hints: config.inlay_hints_type,
            parameter_hints: config.inlay_hints_parameter,
            chaining_hints: config.inlay_hints_chaining,
            max_length: config.inlay_hints_max_length,
        },
-        cargo_watch: CheckOptions {
+        check: CheckConfig {
            enable: config.cargo_watch_enable,
            args: config.cargo_watch_args.clone(),
            command: config.cargo_watch_command.clone(),
@@ -109,6 +109,7 @@ fn get_options(
        },
        rustfmt_args: config.rustfmt_args.clone(),
        vscode_lldb: config.vscode_lldb,
+        proc_macro_srv: None, // FIXME: get this from config
    }
 }
@@ -210,7 +211,7 @@ pub fn main_loop(
            config.lru_capacity,
            &globs,
            Watch(!config.use_client_watching),
-            get_options(&config, text_document_caps),
+            get_config(&config, text_document_caps),
            feature_flags,
        )
    };
@@ -435,7 +436,7 @@ fn loop_turn(
                                .to_owned();
                            world_state.update_configuration(
                                new_config.lru_capacity,
-                                get_options(&new_config, text_document_caps),
+                                get_config(&new_config, text_document_caps),
                                get_feature_flags(&new_config, connection),
                            );
                        }
@@ -498,7 +499,7 @@ fn loop_turn(
        update_file_notifications_on_threadpool(
            pool,
            world_state.snapshot(),
-            world_state.options.publish_decorations,
+            world_state.config.publish_decorations,
            task_sender.clone(),
            loop_state.subscriptions.subscriptions(),
        )
@@ -808,14 +809,14 @@ fn send_startup_progress(sender: &Sender<Message>, loop_state: &mut LoopState) {
        ),
        _ => {}
    }
-}
-fn send_startup_progress_notif(sender: &Sender<Message>, work_done_progress: WorkDoneProgress) {
+    fn send_startup_progress_notif(sender: &Sender<Message>, work_done_progress: WorkDoneProgress) {
-    let notif = notification_new::<req::Progress>(req::ProgressParams {
+        let notif = notification_new::<req::Progress>(req::ProgressParams {
-        token: req::ProgressToken::String("rustAnalyzer/startup".into()),
+            token: req::ProgressToken::String("rustAnalyzer/startup".into()),
-        value: req::ProgressParamsValue::WorkDone(work_done_progress),
+            value: req::ProgressParamsValue::WorkDone(work_done_progress),
-    });
+        });
-    sender.send(notif.into()).unwrap();
+        sender.send(notif.into()).unwrap();
+    }
 }
 struct PoolDispatcher<'a> {
diff --git a/crates/rust-analyzer/src/main_loop/handlers.rs b/crates/rust-analyzer/src/main_loop/handlers.rs
index f60a3f0a0..d5cb5d137 100644
--- a/crates/rust-analyzer/src/main_loop/handlers.rs
+++ b/crates/rust-analyzer/src/main_loop/handlers.rs
@@ -19,7 +19,7 @@ use lsp_types::{
    TextEdit, WorkspaceEdit,
 };
 use ra_ide::{
-    Assist, AssistId, CompletionOptions, FileId, FilePosition, FileRange, Query, RangeInfo,
+    Assist, AssistId, CompletionConfig, FileId, FilePosition, FileRange, Query, RangeInfo,
    Runnable, RunnableKind, SearchScope,
 };
 use ra_prof::profile;
@@ -425,7 +425,7 @@ pub fn handle_completion(
        return Ok(None);
    }
-    let options = CompletionOptions {
+    let config = CompletionConfig {
        enable_postfix_completions: world.feature_flags.get("completion.enable-postfix"),
        add_call_parenthesis: world.feature_flags.get("completion.insertion.add-call-parenthesis"),
        add_call_argument_snippets: world
@@ -433,7 +433,7 @@ pub fn handle_completion(
            .get("completion.insertion.add-argument-snippets"),
    };
-    let items = match world.analysis().completions(position, &options)? {
+    let items = match world.analysis().completions(position, &config)? {
        None => return Ok(None),
        Some(items) => items,
    };
@@ -457,7 +457,7 @@ pub fn handle_folding_range(
    let ctx = FoldConvCtx {
        text: &text,
        line_index: &line_index,
-        line_folding_only: world.options.line_folding_only,
+        line_folding_only: world.config.line_folding_only,
    };
    let res = Some(folds.into_iter().map_conv_with(&ctx).collect());
    Ok(res)
@@ -611,7 +611,7 @@ pub fn handle_formatting(
    let end_position = TextUnit::of_str(&file).conv_with(&file_line_index);
    let mut rustfmt = process::Command::new("rustfmt");
-    rustfmt.args(&world.options.rustfmt_args);
+    rustfmt.args(&world.config.rustfmt_args);
    if let Some(&crate_id) = crate_ids.first() {
        // Assume all crates are in the same edition
        let edition = world.analysis().crate_edition(crate_id)?;
@@ -815,7 +815,7 @@ pub fn handle_code_lens(
        };
        lenses.push(lens);
-        if world.options.vscode_lldb {
+        if world.config.vscode_lldb {
            if r.args[0] == "run" {
                r.args[0] = "build".into();
            } else {
@@ -1028,7 +1028,7 @@ pub fn handle_inlay_hints(
    let analysis = world.analysis();
    let line_index = analysis.file_line_index(file_id)?;
    Ok(analysis
-        .inlay_hints(file_id, &world.options.inlay_hints)?
+        .inlay_hints(file_id, &world.config.inlay_hints)?
        .into_iter()
        .map_conv_with(&line_index)
        .collect())
diff --git a/crates/rust-analyzer/src/world.rs b/crates/rust-analyzer/src/world.rs
index ad096a1d8..acb729bae 100644
--- a/crates/rust-analyzer/src/world.rs
+++ b/crates/rust-analyzer/src/world.rs
@@ -11,9 +11,9 @@ use std::{
 use crossbeam_channel::{unbounded, Receiver};
 use lsp_types::Url;
 use parking_lot::RwLock;
-use ra_cargo_watch::{url_from_path_with_drive_lowercasing, CheckOptions, CheckWatcher};
+use ra_flycheck::{url_from_path_with_drive_lowercasing, CheckConfig, CheckWatcher};
 use ra_ide::{
-    Analysis, AnalysisChange, AnalysisHost, CrateGraph, FileId, InlayHintsOptions, LibraryData,
+    Analysis, AnalysisChange, AnalysisHost, CrateGraph, FileId, InlayHintsConfig, LibraryData,
    SourceRootId,
 };
 use ra_project_model::{get_rustc_cfg_options, ProcMacroClient, ProjectWorkspace};
@@ -31,7 +31,7 @@ use crate::{
 use ra_db::ExternSourceId;
 use rustc_hash::{FxHashMap, FxHashSet};
-fn create_watcher(workspaces: &[ProjectWorkspace], options: &Options) -> Option<CheckWatcher> {
+fn create_watcher(workspaces: &[ProjectWorkspace], config: &Config) -> Option<CheckWatcher> {
    // FIXME: Figure out the multi-workspace situation
    workspaces
        .iter()
@@ -41,7 +41,7 @@ fn create_watcher(workspaces: &[ProjectWorkspace], options: &Options) -> Option<
        })
        .map(|cargo| {
            let cargo_project_root = cargo.workspace_root().to_path_buf();
-            Some(CheckWatcher::new(&options.cargo_watch, cargo_project_root))
+            Some(CheckWatcher::new(config.check.clone(), cargo_project_root))
        })
        .unwrap_or_else(|| {
            log::warn!("Cargo check watching only supported for cargo workspaces, disabling");
@@ -50,14 +50,15 @@ fn create_watcher(workspaces: &[ProjectWorkspace], options: &Options) -> Option<
 }
 #[derive(Debug, Clone)]
-pub struct Options {
+pub struct Config {
    pub publish_decorations: bool,
    pub supports_location_link: bool,
    pub line_folding_only: bool,
-    pub inlay_hints: InlayHintsOptions,
+    pub inlay_hints: InlayHintsConfig,
    pub rustfmt_args: Vec<String>,
-    pub cargo_watch: CheckOptions,
+    pub check: CheckConfig,
    pub vscode_lldb: bool,
+    pub proc_macro_srv: Option<String>,
 }
 /// `WorldState` is the primary mutable state of the language server
@@ -67,7 +68,7 @@ pub struct Options {
 /// incremental salsa database.
 #[derive(Debug)]
 pub struct WorldState {
-    pub options: Options,
+    pub config: Config,
    pub feature_flags: Arc<FeatureFlags>,
    pub roots: Vec<PathBuf>,
    pub workspaces: Arc<Vec<ProjectWorkspace>>,
@@ -81,7 +82,7 @@ pub struct WorldState {
 /// An immutable snapshot of the world's state at a point in time.
 pub struct WorldSnapshot {
-    pub options: Options,
+    pub config: Config,
    pub feature_flags: Arc<FeatureFlags>,
    pub workspaces: Arc<Vec<ProjectWorkspace>>,
    pub analysis: Analysis,
@@ -97,7 +98,7 @@ impl WorldState {
        lru_capacity: Option<usize>,
        exclude_globs: &[Glob],
        watch: Watch,
-        options: Options,
+        config: Config,
        feature_flags: FeatureFlags,
    ) -> WorldState {
        let mut change = AnalysisChange::new();
@@ -167,8 +168,23 @@ impl WorldState {
            vfs_file.map(|f| FileId(f.0))
        };
-        let proc_macro_client =
+        let proc_macro_client = match &config.proc_macro_srv {
-            ProcMacroClient::extern_process(std::path::Path::new("ra_proc_macro_srv"));
+            None => ProcMacroClient::dummy(),
+            Some(srv) => {
+                let path = Path::new(&srv);
+                match ProcMacroClient::extern_process(path) {
+                    Ok(it) => it,
+                    Err(err) => {
+                        log::error!(
+                            "Fail to run ra_proc_macro_srv from path {}, error : {}",
+                            path.to_string_lossy(),
+                            err
+                        );
+                        ProcMacroClient::dummy()
+                    }
+                }
+            }
+        };
        workspaces
            .iter()
@@ -185,12 +201,12 @@ impl WorldState {
            });
        change.set_crate_graph(crate_graph);
-        let check_watcher = create_watcher(&workspaces, &options);
+        let check_watcher = create_watcher(&workspaces, &config);
        let mut analysis_host = AnalysisHost::new(lru_capacity);
        analysis_host.apply_change(change);
        WorldState {
-            options,
+            config: config,
            feature_flags: Arc::new(feature_flags),
            roots: folder_roots,
            workspaces: Arc::new(workspaces),
@@ -206,13 +222,13 @@ impl WorldState {
    pub fn update_configuration(
        &mut self,
        lru_capacity: Option<usize>,
-        options: Options,
+        config: Config,
        feature_flags: FeatureFlags,
    ) {
        self.feature_flags = Arc::new(feature_flags);
        self.analysis_host.update_lru_capacity(lru_capacity);
-        self.check_watcher = create_watcher(&self.workspaces, &options);
+        self.check_watcher = create_watcher(&self.workspaces, &config);
-        self.options = options;
+        self.config = config;
    }
    /// Returns a vec of libraries
@@ -268,7 +284,7 @@ impl WorldState {
    pub fn snapshot(&self) -> WorldSnapshot {
        WorldSnapshot {
-            options: self.options.clone(),
+            config: self.config.clone(),
            feature_flags: Arc::clone(&self.feature_flags),
            workspaces: Arc::clone(&self.workspaces),
            analysis: self.analysis_host.analysis(),
diff --git a/crates/rust-analyzer/tests/heavy_tests/main.rs b/crates/rust-analyzer/tests/heavy_tests/main.rs
index 145429571..5af5eaad2 100644
--- a/crates/rust-analyzer/tests/heavy_tests/main.rs
+++ b/crates/rust-analyzer/tests/heavy_tests/main.rs
@@ -9,7 +9,7 @@ use lsp_types::{
 };
 use rust_analyzer::req::{
    CodeActionParams, CodeActionRequest, Completion, CompletionParams, DidOpenTextDocument,
-    Formatting, OnEnter, Runnables, RunnablesParams,
+    Formatting, GotoDefinition, OnEnter, Runnables, RunnablesParams,
 };
 use serde_json::json;
 use tempfile::TempDir;
@@ -581,3 +581,47 @@ version = \"0.0.0\"
        }),
    );
 }
+#[test]
+fn resolve_include_concat_env() {
+    if skip_slow_tests() {
+        return;
+    }
+    let server = Project::with_fixture(
+        r###"
+//- Cargo.toml
+[package]
+name = "foo"
+version = "0.0.0"
+//- build.rs
+use std::{env, fs, path::Path};
+fn main() {
+    let out_dir = env::var_os("OUT_DIR").unwrap();
+    let dest_path = Path::new(&out_dir).join("hello.rs");
+    fs::write(
+        &dest_path,
+        r#"pub fn message() -> &'static str { "Hello, World!" }"#,
+    )
+    .unwrap();
+    println!("cargo:rerun-if-changed=build.rs");
+}
+//- src/main.rs
+include!(concat!(env!("OUT_DIR"), "/hello.rs"));
+fn main() { message(); }
+"###,
+    )
+    .with_config(|config| {
+        config.cargo_features.load_out_dirs_from_check = true;
+    })
+    .server();
+    server.wait_until_workspace_is_loaded();
+    let res = server.send_request::<GotoDefinition>(TextDocumentPositionParams::new(
+        server.doc_id("src/main.rs"),
+        Position::new(2, 15),
+    ));
+    assert!(format!("{}", res).contains("hello.rs"));
+}
diff --git a/crates/rust-analyzer/tests/heavy_tests/support.rs b/crates/rust-analyzer/tests/heavy_tests/support.rs
index 67f3c9332..d8bed6d7f 100644
--- a/crates/rust-analyzer/tests/heavy_tests/support.rs
+++ b/crates/rust-analyzer/tests/heavy_tests/support.rs
@@ -27,11 +27,12 @@ pub struct Project<'a> {
    with_sysroot: bool,
    tmp_dir: Option<TempDir>,
    roots: Vec<PathBuf>,
+    config: Option<Box<dyn Fn(&mut ServerConfig)>>,
 }
 impl<'a> Project<'a> {
    pub fn with_fixture(fixture: &str) -> Project {
-        Project { fixture, tmp_dir: None, roots: vec![], with_sysroot: false }
+        Project { fixture, tmp_dir: None, roots: vec![], with_sysroot: false, config: None }
    }
    pub fn tmp_dir(mut self, tmp_dir: TempDir) -> Project<'a> {
@@ -49,6 +50,11 @@ impl<'a> Project<'a> {
        self
    }
+    pub fn with_config(mut self, config: impl Fn(&mut ServerConfig) + 'static) -> Project<'a> {
+        self.config = Some(Box::new(config));
+        self
+    }
    pub fn server(self) -> Server {
        let tmp_dir = self.tmp_dir.unwrap_or_else(|| TempDir::new().unwrap());
        static INIT: Once = Once::new();
@@ -72,7 +78,14 @@ impl<'a> Project<'a> {
        let roots = self.roots.into_iter().map(|root| tmp_dir.path().join(root)).collect();
-        Server::new(tmp_dir, self.with_sysroot, roots, paths)
+        let mut config =
+            ServerConfig { with_sysroot: self.with_sysroot, ..ServerConfig::default() };
+        if let Some(f) = &self.config {
+            f(&mut config)
+        }
+        Server::new(tmp_dir, config, roots, paths)
    }
 }
@@ -92,7 +105,7 @@ pub struct Server {
 impl Server {
    fn new(
        dir: TempDir,
-        with_sysroot: bool,
+        config: ServerConfig,
        roots: Vec<PathBuf>,
        files: Vec<(PathBuf, String)>,
    ) -> Server {
@@ -118,7 +131,7 @@ impl Server {
                        window: None,
                        experimental: None,
                    },
-                    ServerConfig { with_sysroot, ..ServerConfig::default() },
+                    config,
                    connection,
                )
                .unwrap()
@@ -188,6 +201,7 @@ impl Server {
        self.client.sender.send(r.into()).unwrap();
        while let Some(msg) = self.recv() {
            match msg {
+                Message::Request(req) if req.method == "window/workDoneProgress/create" => (),
                Message::Request(req) => panic!("unexpected request: {:?}", req),
                Message::Notification(_) => (),
                Message::Response(res) => {
diff --git a/docs/user/features.md b/docs/user/features.md
index 56d2969fd..8aeec2e81 100644
--- a/docs/user/features.md
+++ b/docs/user/features.md
@@ -81,6 +81,12 @@ Join selected lines into one, smartly fixing up whitespace and trailing commas.
 Shows the parse tree of the current file. It exists mostly for debugging
 rust-analyzer itself.
+You can hover over syntax nodes in the opened text file to see the appropriate
+rust code that it refers to and the rust editor will also highlight the proper
+text range.
+<img src="https://user-images.githubusercontent.com/36276403/78043783-7425e180-737c-11ea-8653-b02b773c5aa1.png" alt="demo" height="200px" >
 #### Expand Macro Recursively
 Shows the full macro expansion of the macro at current cursor.
diff --git a/editors/code/package-lock.json b/editors/code/package-lock.json
index b7220d8e2..955a05066 100644
--- a/editors/code/package-lock.json
+++ b/editors/code/package-lock.json
@@ -84,9 +84,9 @@
            "dev": true
        },
        "@types/node": {
-            "version": "12.12.30",
+            "version": "12.12.34",
-            "resolved": "https://registry.npmjs.org/@types/node/-/node-12.12.30.tgz",
+            "resolved": "https://registry.npmjs.org/@types/node/-/node-12.12.34.tgz",
-            "integrity": "sha512-sz9MF/zk6qVr3pAnM0BSQvYIBK44tS75QC5N+VbWSE4DjCV/pJ+UzCW/F+vVnl7TkOPcuwQureKNtSSwjBTaMg==",
+            "integrity": "sha512-BneGN0J9ke24lBRn44hVHNeDlrXRYF+VRp0HbSUNnEZahXGAysHZIqnf/hER6aabdBgzM4YOV4jrR8gj4Zfi0g==",
            "dev": true
        },
        "@types/node-fetch": {
@@ -115,45 +115,56 @@
            "dev": true
        },
        "@typescript-eslint/eslint-plugin": {
-            "version": "2.24.0",
+            "version": "2.26.0",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/eslint-plugin/-/eslint-plugin-2.24.0.tgz",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/eslint-plugin/-/eslint-plugin-2.26.0.tgz",
-            "integrity": "sha512-wJRBeaMeT7RLQ27UQkDFOu25MqFOBus8PtOa9KaT5ZuxC1kAsd7JEHqWt4YXuY9eancX0GK9C68i5OROnlIzBA==",
+            "integrity": "sha512-4yUnLv40bzfzsXcTAtZyTjbiGUXMrcIJcIMioI22tSOyAxpdXiZ4r7YQUU8Jj6XXrLz9d5aMHPQf5JFR7h27Nw==",
            "dev": true,
            "requires": {
-                "@typescript-eslint/experimental-utils": "2.24.0",
+                "@typescript-eslint/experimental-utils": "2.26.0",
-                "eslint-utils": "^1.4.3",
                "functional-red-black-tree": "^1.0.1",
                "regexpp": "^3.0.0",
                "tsutils": "^3.17.1"
            }
        },
        "@typescript-eslint/experimental-utils": {
-            "version": "2.24.0",
+            "version": "2.26.0",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/experimental-utils/-/experimental-utils-2.24.0.tgz",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/experimental-utils/-/experimental-utils-2.26.0.tgz",
-            "integrity": "sha512-DXrwuXTdVh3ycNCMYmWhUzn/gfqu9N0VzNnahjiDJvcyhfBy4gb59ncVZVxdp5XzBC77dCncu0daQgOkbvPwBw==",
+            "integrity": "sha512-RELVoH5EYd+JlGprEyojUv9HeKcZqF7nZUGSblyAw1FwOGNnmQIU8kxJ69fttQvEwCsX5D6ECJT8GTozxrDKVQ==",
            "dev": true,
            "requires": {
                "@types/json-schema": "^7.0.3",
-                "@typescript-eslint/typescript-estree": "2.24.0",
+                "@typescript-eslint/typescript-estree": "2.26.0",
-                "eslint-scope": "^5.0.0"
+                "eslint-scope": "^5.0.0",
+                "eslint-utils": "^2.0.0"
+            },
+            "dependencies": {
+                "eslint-utils": {
+                    "version": "2.0.0",
+                    "resolved": "https://registry.npmjs.org/eslint-utils/-/eslint-utils-2.0.0.tgz",
+                    "integrity": "sha512-0HCPuJv+7Wv1bACm8y5/ECVfYdfsAm9xmVb7saeFlxjPYALefjhbYoCkBjPdPzGH8wWyTpAez82Fh3VKYEZ8OA==",
+                    "dev": true,
+                    "requires": {
+                        "eslint-visitor-keys": "^1.1.0"
+                    }
+                }
            }
        },
        "@typescript-eslint/parser": {
-            "version": "2.24.0",
+            "version": "2.26.0",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/parser/-/parser-2.24.0.tgz",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/parser/-/parser-2.26.0.tgz",
-            "integrity": "sha512-H2Y7uacwSSg8IbVxdYExSI3T7uM1DzmOn2COGtCahCC3g8YtM1xYAPi2MAHyfPs61VKxP/J/UiSctcRgw4G8aw==",
+            "integrity": "sha512-+Xj5fucDtdKEVGSh9353wcnseMRkPpEAOY96EEenN7kJVrLqy/EVwtIh3mxcUz8lsFXW1mT5nN5vvEam/a5HiQ==",
            "dev": true,
            "requires": {
                "@types/eslint-visitor-keys": "^1.0.0",
-                "@typescript-eslint/experimental-utils": "2.24.0",
+                "@typescript-eslint/experimental-utils": "2.26.0",
-                "@typescript-eslint/typescript-estree": "2.24.0",
+                "@typescript-eslint/typescript-estree": "2.26.0",
                "eslint-visitor-keys": "^1.1.0"
            }
        },
        "@typescript-eslint/typescript-estree": {
-            "version": "2.24.0",
+            "version": "2.26.0",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-2.24.0.tgz",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-2.26.0.tgz",
-            "integrity": "sha512-RJ0yMe5owMSix55qX7Mi9V6z2FDuuDpN6eR5fzRJrp+8in9UF41IGNQHbg5aMK4/PjVaEQksLvz0IA8n+Mr/FA==",
+            "integrity": "sha512-3x4SyZCLB4zsKsjuhxDLeVJN6W29VwBnYpCsZ7vIdPel9ZqLfIZJgJXO47MNUkurGpQuIBALdPQKtsSnWpE1Yg==",
            "dev": true,
            "requires": {
                "debug": "^4.1.1",
@@ -1388,9 +1399,9 @@
            }
        },
        "rollup": {
-            "version": "2.1.0",
+            "version": "2.3.1",
-            "resolved": "https://registry.npmjs.org/rollup/-/rollup-2.1.0.tgz",
+            "resolved": "https://registry.npmjs.org/rollup/-/rollup-2.3.1.tgz",
-            "integrity": "sha512-gfE1455AEazVVTJoeQtcOq/U6GSxwoj4XPSWVsuWmgIxj7sBQNLDOSA82PbdMe+cP8ql8fR1jogPFe8Wg8g4SQ==",
+            "integrity": "sha512-BRjzOauORe+R0U0I6SkMTSG22nYmtztR/TaBl0SvbXgc3VAxBDrZoB6HROiK0S5px1pUBnLnjBkbzmVuwC9Q1Q==",
            "dev": true,
            "requires": {
                "fsevents": "~2.1.2"
diff --git a/editors/code/package.json b/editors/code/package.json
index 37e083220..ba31c4e63 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -39,13 +39,13 @@
    "devDependencies": {
        "@rollup/plugin-commonjs": "^11.0.2",
        "@rollup/plugin-node-resolve": "^7.1.1",
-        "@types/node": "^12.12.30",
+        "@types/node": "^12.12.34",
        "@types/node-fetch": "^2.5.5",
        "@types/vscode": "^1.43.0",
-        "@typescript-eslint/eslint-plugin": "^2.24.0",
+        "@typescript-eslint/eslint-plugin": "^2.26.0",
-        "@typescript-eslint/parser": "^2.24.0",
+        "@typescript-eslint/parser": "^2.26.0",
        "eslint": "^6.8.0",
-        "rollup": "^2.1.0",
+        "rollup": "^2.3.1",
        "tslib": "^1.11.1",
        "typescript": "^3.8.3",
        "typescript-formatter": "^7.2.2",
diff --git a/editors/code/src/client.ts b/editors/code/src/client.ts
index d72ecc58f..f909f8db2 100644
--- a/editors/code/src/client.ts
+++ b/editors/code/src/client.ts
@@ -30,15 +30,14 @@ export function configToServerOptions(config: Config) {
    };
 }
-export async function createClient(config: Config, serverPath: string): Promise<lc.LanguageClient> {
+export async function createClient(config: Config, serverPath: string, cwd: string): Promise<lc.LanguageClient> {
    // '.' Is the fallback if no folder is open
    // TODO?: Workspace folders support Uri's (eg: file://test.txt).
    // It might be a good idea to test if the uri points to a file.
-    const workspaceFolderPath = vscode.workspace.workspaceFolders?.[0]?.uri.fsPath ?? '.';
    const run: lc.Executable = {
        command: serverPath,
-        options: { cwd: workspaceFolderPath },
+        options: { cwd },
    };
    const serverOptions: lc.ServerOptions = {
        run,
diff --git a/editors/code/src/commands/syntax_tree.ts b/editors/code/src/commands/syntax_tree.ts
index 2e08e8f11..996c7a716 100644
--- a/editors/code/src/commands/syntax_tree.ts
+++ b/editors/code/src/commands/syntax_tree.ts
@@ -1,8 +1,10 @@
 import * as vscode from 'vscode';
 import * as ra from '../rust-analyzer-api';
-import { Ctx, Cmd } from '../ctx';
+import { Ctx, Cmd, Disposable } from '../ctx';
-import { isRustDocument } from '../util';
+import { isRustDocument, RustEditor, isRustEditor, sleep } from '../util';
+const AST_FILE_SCHEME = "rust-analyzer";
 // Opens the virtual file that will show the syntax tree
 //
@@ -10,35 +12,13 @@ import { isRustDocument } from '../util';
 export function syntaxTree(ctx: Ctx): Cmd {
    const tdcp = new TextDocumentContentProvider(ctx);
-    ctx.pushCleanup(
+    void new AstInspector(ctx);
-        vscode.workspace.registerTextDocumentContentProvider(
-            'rust-analyzer',
+    ctx.pushCleanup(vscode.workspace.registerTextDocumentContentProvider(AST_FILE_SCHEME, tdcp));
-            tdcp,
-        ),
-    );
-    vscode.workspace.onDidChangeTextDocument(
-        (event: vscode.TextDocumentChangeEvent) => {
-            const doc = event.document;
-            if (!isRustDocument(doc)) return;
-            afterLs(() => tdcp.eventEmitter.fire(tdcp.uri));
-        },
-        null,
-        ctx.subscriptions,
-    );
-    vscode.window.onDidChangeActiveTextEditor(
-        (editor: vscode.TextEditor | undefined) => {
-            if (!editor || !isRustDocument(editor.document)) return;
-            tdcp.eventEmitter.fire(tdcp.uri);
-        },
-        null,
-        ctx.subscriptions,
-    );
    return async () => {
        const editor = vscode.window.activeTextEditor;
-        const rangeEnabled = !!(editor && !editor.selection.isEmpty);
+        const rangeEnabled = !!editor && !editor.selection.isEmpty;
        const uri = rangeEnabled
            ? vscode.Uri.parse(`${tdcp.uri.toString()}?range=true`)
@@ -48,45 +28,126 @@ export function syntaxTree(ctx: Ctx): Cmd {
        tdcp.eventEmitter.fire(uri);
-        return vscode.window.showTextDocument(
+        void await vscode.window.showTextDocument(document, {
-            document,
+            viewColumn: vscode.ViewColumn.Two,
-            vscode.ViewColumn.Two,
+            preserveFocus: true
-            true,
+        });
-        );
    };
 }
-// We need to order this after LS updates, but there's no API for that.
-// Hence, good old setTimeout.
-function afterLs(f: () => void) {
-    setTimeout(f, 10);
-}
 class TextDocumentContentProvider implements vscode.TextDocumentContentProvider {
-    uri = vscode.Uri.parse('rust-analyzer://syntaxtree');
+    readonly uri = vscode.Uri.parse('rust-analyzer://syntaxtree');
-    eventEmitter = new vscode.EventEmitter<vscode.Uri>();
+    readonly eventEmitter = new vscode.EventEmitter<vscode.Uri>();
    constructor(private readonly ctx: Ctx) {
+        vscode.workspace.onDidChangeTextDocument(this.onDidChangeTextDocument, this, ctx.subscriptions);
+        vscode.window.onDidChangeActiveTextEditor(this.onDidChangeActiveTextEditor, this, ctx.subscriptions);
    }
-    provideTextDocumentContent(uri: vscode.Uri): vscode.ProviderResult<string> {
+    private onDidChangeTextDocument(event: vscode.TextDocumentChangeEvent) {
-        const editor = vscode.window.activeTextEditor;
+        if (isRustDocument(event.document)) {
-        const client = this.ctx.client;
+            // We need to order this after language server updates, but there's no API for that.
-        if (!editor || !client) return '';
+            // Hence, good old sleep().
+            void sleep(10).then(() => this.eventEmitter.fire(this.uri));
+        }
+    }
+    private onDidChangeActiveTextEditor(editor: vscode.TextEditor | undefined) {
+        if (editor && isRustEditor(editor)) {
+            this.eventEmitter.fire(this.uri);
+        }
+    }
+    provideTextDocumentContent(uri: vscode.Uri, ct: vscode.CancellationToken): vscode.ProviderResult<string> {
+        const rustEditor = this.ctx.activeRustEditor;
+        if (!rustEditor) return '';
        // When the range based query is enabled we take the range of the selection
-        const range = uri.query === 'range=true' && !editor.selection.isEmpty
+        const range = uri.query === 'range=true' && !rustEditor.selection.isEmpty
-            ? client.code2ProtocolConverter.asRange(editor.selection)
+            ? this.ctx.client.code2ProtocolConverter.asRange(rustEditor.selection)
            : null;
-        return client.sendRequest(ra.syntaxTree, {
+        const params = { textDocument: { uri: rustEditor.document.uri.toString() }, range, };
-            textDocument: { uri: editor.document.uri.toString() },
+        return this.ctx.client.sendRequest(ra.syntaxTree, params, ct);
-            range,
-        });
    }
    get onDidChange(): vscode.Event<vscode.Uri> {
        return this.eventEmitter.event;
    }
 }
+// FIXME: consider implementing this via the Tree View API?
+// https://code.visualstudio.com/api/extension-guides/tree-view
+class AstInspector implements vscode.HoverProvider, Disposable {
+    private static readonly astDecorationType = vscode.window.createTextEditorDecorationType({
+        fontStyle: "normal",
+        border: "#ffffff 1px solid",
+    });
+    private rustEditor: undefined | RustEditor;
+    constructor(ctx: Ctx) {
+        ctx.pushCleanup(vscode.languages.registerHoverProvider({ scheme: AST_FILE_SCHEME }, this));
+        vscode.workspace.onDidCloseTextDocument(this.onDidCloseTextDocument, this, ctx.subscriptions);
+        vscode.window.onDidChangeVisibleTextEditors(this.onDidChangeVisibleTextEditors, this, ctx.subscriptions);
+        ctx.pushCleanup(this);
+    }
+    dispose() {
+        this.setRustEditor(undefined);
+    }
+    private onDidCloseTextDocument(doc: vscode.TextDocument) {
+        if (this.rustEditor && doc.uri.toString() === this.rustEditor.document.uri.toString()) {
+            this.setRustEditor(undefined);
+        }
+    }
+    private onDidChangeVisibleTextEditors(editors: vscode.TextEditor[]) {
+        if (editors.every(suspect => suspect.document.uri.scheme !== AST_FILE_SCHEME)) {
+            this.setRustEditor(undefined);
+            return;
+        }
+        this.setRustEditor(editors.find(isRustEditor));
+    }
+    private setRustEditor(newRustEditor: undefined | RustEditor) {
+        if (newRustEditor !== this.rustEditor) {
+            this.rustEditor?.setDecorations(AstInspector.astDecorationType, []);
+        }
+        this.rustEditor = newRustEditor;
+    }
+    provideHover(doc: vscode.TextDocument, hoverPosition: vscode.Position): vscode.ProviderResult<vscode.Hover> {
+        if (!this.rustEditor) return;
+        const astTextLine = doc.lineAt(hoverPosition.line);
+        const rustTextRange = this.parseRustTextRange(this.rustEditor.document, astTextLine.text);
+        if (!rustTextRange) return;
+        this.rustEditor.setDecorations(AstInspector.astDecorationType, [rustTextRange]);
+        this.rustEditor.revealRange(rustTextRange);
+        const rustSourceCode = this.rustEditor.document.getText(rustTextRange);
+        const astTextRange = this.findAstRange(astTextLine);
+        return new vscode.Hover(["```rust\n" + rustSourceCode + "\n```"], astTextRange);
+    }
+    private findAstRange(astLine: vscode.TextLine) {
+        const lineOffset = astLine.range.start;
+        const begin = lineOffset.translate(undefined, astLine.firstNonWhitespaceCharacterIndex);
+        const end = lineOffset.translate(undefined, astLine.text.trimEnd().length);
+        return new vscode.Range(begin, end);
+    }
+    private parseRustTextRange(doc: vscode.TextDocument, astLine: string): undefined | vscode.Range {
+        const parsedRange = /\[(\d+); (\d+)\)/.exec(astLine);
+        if (!parsedRange) return;
+        const [begin, end] = parsedRange.slice(1).map(off => doc.positionAt(+off));
+        return new vscode.Range(begin, end);
+    }
+}
diff --git a/editors/code/src/ctx.ts b/editors/code/src/ctx.ts
index d2f49cd23..86b5f3629 100644
--- a/editors/code/src/ctx.ts
+++ b/editors/code/src/ctx.ts
@@ -15,8 +15,13 @@ export class Ctx {
    }
-    static async create(config: Config, extCtx: vscode.ExtensionContext, serverPath: string): Promise<Ctx> {
+    static async create(
-        const client = await createClient(config, serverPath);
+        config: Config,
+        extCtx: vscode.ExtensionContext,
+        serverPath: string,
+        cwd: string,
+    ): Promise<Ctx> {
+        const client = await createClient(config, serverPath, cwd);
        const res = new Ctx(config, extCtx, client, serverPath);
        res.pushCleanup(client.start());
        await client.onReady();
diff --git a/editors/code/src/main.ts b/editors/code/src/main.ts
index a46dbde33..7ba16120c 100644
--- a/editors/code/src/main.ts
+++ b/editors/code/src/main.ts
@@ -13,6 +13,7 @@ import { log, assert } from './util';
 import { PersistentState } from './persistent_state';
 import { fetchRelease, download } from './net';
 import { spawnSync } from 'child_process';
+import { activateTaskProvider } from './tasks';
 let ctx: Ctx | undefined;
@@ -41,11 +42,18 @@ export async function activate(context: vscode.ExtensionContext) {
    const state = new PersistentState(context.globalState);
    const serverPath = await bootstrap(config, state);
+    const workspaceFolder = vscode.workspace.workspaceFolders?.[0];
+    if (workspaceFolder === undefined) {
+        const err = "Cannot activate rust-analyzer when no folder is opened";
+        void vscode.window.showErrorMessage(err);
+        throw new Error(err);
+    }
    // Note: we try to start the server before we activate type hints so that it
    // registers its `onDidChangeDocument` handler before us.
    //
    // This a horribly, horribly wrong way to deal with this problem.
-    ctx = await Ctx.create(config, context, serverPath);
+    ctx = await Ctx.create(config, context, serverPath, workspaceFolder.uri.fsPath);
    // Commands which invokes manually via command palette, shortcut, etc.
@@ -85,6 +93,8 @@ export async function activate(context: vscode.ExtensionContext) {
    ctx.registerCommand('applySourceChange', commands.applySourceChange);
    ctx.registerCommand('selectAndApplySourceChange', commands.selectAndApplySourceChange);
+    ctx.pushCleanup(activateTaskProvider(workspaceFolder));
    activateStatusDisplay(ctx);
    if (!ctx.config.highlightingSemanticTokens) {
diff --git a/editors/code/src/tasks.ts b/editors/code/src/tasks.ts
new file mode 100644
index 000000000..fa1c4a951
--- /dev/null
+++ b/editors/code/src/tasks.ts
@@ -0,0 +1,52 @@
+import * as vscode from 'vscode';
+// This ends up as the `type` key in tasks.json. RLS also uses `cargo` and
+// our configuration should be compatible with it so use the same key.
+const TASK_TYPE = 'cargo';
+export function activateTaskProvider(target: vscode.WorkspaceFolder): vscode.Disposable {
+    const provider: vscode.TaskProvider = {
+        // Detect Rust tasks. Currently we do not do any actual detection
+        // of tasks (e.g. aliases in .cargo/config) and just return a fixed
+        // set of tasks that always exist. These tasks cannot be removed in
+        // tasks.json - only tweaked.
+        provideTasks: () => getStandardCargoTasks(target),
+        // We don't need to implement this.
+        resolveTask: () => undefined,
+    };
+    return vscode.tasks.registerTaskProvider(TASK_TYPE, provider);
+}
+function getStandardCargoTasks(target: vscode.WorkspaceFolder): vscode.Task[] {
+    return [
+        { command: 'build', group: vscode.TaskGroup.Build },
+        { command: 'check', group: vscode.TaskGroup.Build },
+        { command: 'test', group: vscode.TaskGroup.Test },
+        { command: 'clean', group: vscode.TaskGroup.Clean },
+        { command: 'run', group: undefined },
+    ]
+        .map(({ command, group }) => {
+            const vscodeTask = new vscode.Task(
+                // The contents of this object end up in the tasks.json entries.
+                {
+                    type: TASK_TYPE,
+                    command,
+                },
+                // The scope of the task - workspace or specific folder (global
+                // is not supported).
+                target,
+                // The task name, and task source. These are shown in the UI as
+                // `${source}: ${name}`, e.g. `rust: cargo build`.
+                `cargo ${command}`,
+                'rust',
+                // What to do when this command is executed.
+                new vscode.ShellExecution('cargo', [command]),
+                // Problem matchers.
+                ['$rustc'],
+            );
+            vscodeTask.group = group;
+            return vscodeTask;
+        });
+}
diff --git a/editors/code/src/util.ts b/editors/code/src/util.ts
index 978a31751..6f91f81d6 100644
--- a/editors/code/src/util.ts
+++ b/editors/code/src/util.ts
@@ -65,12 +65,12 @@ export async function sendRequestWithRetry<TParam, TRet>(
    throw 'unreachable';
 }
-function sleep(ms: number) {
+export function sleep(ms: number) {
    return new Promise(resolve => setTimeout(resolve, ms));
 }
 export type RustDocument = vscode.TextDocument & { languageId: "rust" };
-export type RustEditor = vscode.TextEditor & { document: RustDocument; id: string };
+export type RustEditor = vscode.TextEditor & { document: RustDocument };
 export function isRustDocument(document: vscode.TextDocument): document is RustDocument {
    return document.languageId === 'rust'