16 files changed, 383 insertions, 89 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 14decc14e..98141f5cd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -72,9 +72,9 @@ checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 
 [[package]]
 name = "backtrace"
-version = "0.3.56"
+version = "0.3.57"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9d117600f438b1707d4e4ae15d3595657288f8235a0eb593e80ecc98ab34e1bc"
+checksum = "78ed203b9ba68b242c62b3fb7480f589dd49829be1edb3fe8fc8b4ffda2dcb8d"
 dependencies = [
  "addr2line",
  "cfg-if",
@@ -168,9 +168,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "chalk-derive"
-version = "0.60.0"
+version = "0.64.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ab0f74445d4fbeaf0217bc1d23978cc73b95b28e8a738b81894580dd646822d2"
+checksum = "d9acf2a9eab79ae7d44cd77ad86a8b1569d7a5e6d9a7db4a0a57a7344dd82c24"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -180,9 +180,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-ir"
-version = "0.60.0"
+version = "0.64.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "294b1fc6210a5b3bd06c1d01dda48a581e2cafec80b8d659139ce45456644be2"
+checksum = "877661627f54ba3666a72943c43b326cb170d60899e50a8426111e7a657ff032"
 dependencies = [
  "bitflags",
  "chalk-derive",
@@ -191,9 +191,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-recursive"
-version = "0.60.0"
+version = "0.64.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b9386936070be4545bfa22b094b7065af79aa2aeaccc945438f1c5ffe74c30a"
+checksum = "072ffcf17243c2aa3e4b9ea6de3d29e7ef64cfdb0ceccaa431965070a1dc1475"
 dependencies = [
  "chalk-derive",
  "chalk-ir",
@@ -204,9 +204,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-solve"
-version = "0.60.0"
+version = "0.64.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7c12a1ec7e850b50a049f27ef9cf5df3056bbd1acbb3eeb44d024e501a641f3a"
+checksum = "97d4920c9ef2b26dd0b98ffdf070e27fa31e0b6f637463132083cee597e3d326"
 dependencies = [
  "chalk-derive",
  "chalk-ir",
@@ -396,6 +396,7 @@ dependencies = [
  "crossbeam-channel",
  "jod-thread",
  "log",
+ "serde",
  "serde_json",
  "stdx",
  "toolchain",
@@ -684,9 +685,9 @@ dependencies = [
 
 [[package]]
 name = "idna"
-version = "0.2.2"
+version = "0.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "89829a5d69c23d348314a7ac337fe39173b61149a9864deabd260983aed48c21"
+checksum = "418a0a6fab821475f634efe3ccc45c013f742efe03d853e8d3355d5cb850ecf8"
 dependencies = [
  "matches",
  "unicode-bidi",
@@ -1292,9 +1293,9 @@ dependencies = [
 
 [[package]]
 name = "redox_syscall"
-version = "0.2.5"
+version = "0.2.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "94341e4e44e24f6b591b59e47a8a027df12e008d73fd5672dbea9cc22f4507d9"
+checksum = "8270314b5ccceb518e7e578952f0b72b88222d02e8f77f5ecf7abbb673539041"
 dependencies = [
  "bitflags",
 ]
@@ -1391,9 +1392,9 @@ dependencies = [
 
 [[package]]
 name = "rustc-ap-rustc_lexer"
-version = "714.0.0"
+version = "716.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a35856f140bed0dc7c7d6ba2134099d337377a3a4e11bfc79bccabf1fd4c9d42"
+checksum = "12eac7554c1d3f49f105f14d53c0f3402220e875983113562701d8e597a0995c"
 dependencies = [
  "unicode-xid",
 ]
diff --git a/crates/flycheck/Cargo.toml b/crates/flycheck/Cargo.toml
index 2a1a21b28..18b9ce7df 100644
--- a/crates/flycheck/Cargo.toml
+++ b/crates/flycheck/Cargo.toml
@@ -13,6 +13,7 @@ doctest = false
 crossbeam-channel = "0.5.0"
 log = "0.4.8"
 cargo_metadata = "0.13"
+serde = { version = "1.0.106", features = ["derive"] }
 serde_json = "1.0.48"
 jod-thread = "0.1.1"
 
diff --git a/crates/flycheck/src/lib.rs b/crates/flycheck/src/lib.rs
index e2a59497a..1682d8bde 100644
--- a/crates/flycheck/src/lib.rs
+++ b/crates/flycheck/src/lib.rs
@@ -4,13 +4,14 @@
 
 use std::{
     fmt,
-    io::{self, BufReader},
+    io::{self, BufRead, BufReader},
     path::PathBuf,
     process::{self, Command, Stdio},
     time::Duration,
 };
 
 use crossbeam_channel::{never, select, unbounded, Receiver, Sender};
+use serde::Deserialize;
 use stdx::JodChild;
 
 pub use cargo_metadata::diagnostic::{
@@ -128,7 +129,7 @@ struct FlycheckActor {
 
 enum Event {
     Restart(Restart),
-    CheckEvent(Option<cargo_metadata::Message>),
+    CheckEvent(Option<CargoMessage>),
 }
 
 impl FlycheckActor {
@@ -180,21 +181,16 @@ impl FlycheckActor {
                     self.progress(Progress::DidFinish(res));
                 }
                 Event::CheckEvent(Some(message)) => match message {
-                    cargo_metadata::Message::CompilerArtifact(msg) => {
+                    CargoMessage::CompilerArtifact(msg) => {
                         self.progress(Progress::DidCheckCrate(msg.target.name));
                     }
 
-                    cargo_metadata::Message::CompilerMessage(msg) => {
+                    CargoMessage::Diagnostic(msg) => {
                         self.send(Message::AddDiagnostic {
                             workspace_root: self.workspace_root.clone(),
-                            diagnostic: msg.message,
+                            diagnostic: msg,
                         });
                     }
-
-                    cargo_metadata::Message::BuildScriptExecuted(_)
-                    | cargo_metadata::Message::BuildFinished(_)
-                    | cargo_metadata::Message::TextLine(_)
-                    | _ => {}
                 },
             }
         }
@@ -261,7 +257,7 @@ struct CargoHandle {
     child: JodChild,
     #[allow(unused)]
     thread: jod_thread::JoinHandle<io::Result<bool>>,
-    receiver: Receiver<cargo_metadata::Message>,
+    receiver: Receiver<CargoMessage>,
 }
 
 impl CargoHandle {
@@ -294,14 +290,11 @@ impl CargoHandle {
 
 struct CargoActor {
     child_stdout: process::ChildStdout,
-    sender: Sender<cargo_metadata::Message>,
+    sender: Sender<CargoMessage>,
 }
 
 impl CargoActor {
-    fn new(
-        child_stdout: process::ChildStdout,
-        sender: Sender<cargo_metadata::Message>,
-    ) -> CargoActor {
+    fn new(child_stdout: process::ChildStdout, sender: Sender<CargoMessage>) -> CargoActor {
         CargoActor { child_stdout, sender }
     }
     fn run(self) -> io::Result<bool> {
@@ -315,7 +308,7 @@ impl CargoActor {
         // erroneus output.
         let stdout = BufReader::new(self.child_stdout);
         let mut read_at_least_one_message = false;
-        for message in cargo_metadata::Message::parse_stream(stdout) {
+        for message in stdout.lines() {
             let message = match message {
                 Ok(message) => message,
                 Err(err) => {
@@ -326,13 +319,44 @@ impl CargoActor {
 
             read_at_least_one_message = true;
 
-            // Skip certain kinds of messages to only spend time on what's useful
-            match &message {
-                cargo_metadata::Message::CompilerArtifact(artifact) if artifact.fresh => (),
-                cargo_metadata::Message::BuildScriptExecuted(_) => (),
-                _ => self.sender.send(message).unwrap(),
+            // Try to deserialize a message from Cargo or Rustc.
+            let mut deserializer = serde_json::Deserializer::from_str(&message);
+            deserializer.disable_recursion_limit();
+            if let Ok(message) = JsonMessage::deserialize(&mut deserializer) {
+                match message {
+                    // Skip certain kinds of messages to only spend time on what's useful
+                    JsonMessage::Cargo(message) => match message {
+                        cargo_metadata::Message::CompilerArtifact(artifact) if !artifact.fresh => {
+                            self.sender.send(CargoMessage::CompilerArtifact(artifact)).unwrap()
+                        }
+                        cargo_metadata::Message::CompilerMessage(msg) => {
+                            self.sender.send(CargoMessage::Diagnostic(msg.message)).unwrap()
+                        }
+
+                        cargo_metadata::Message::CompilerArtifact(_)
+                        | cargo_metadata::Message::BuildScriptExecuted(_)
+                        | cargo_metadata::Message::BuildFinished(_)
+                        | cargo_metadata::Message::TextLine(_)
+                        | _ => (),
+                    },
+                    JsonMessage::Rustc(message) => {
+                        self.sender.send(CargoMessage::Diagnostic(message)).unwrap()
+                    }
+                }
             }
         }
         Ok(read_at_least_one_message)
     }
 }
+
+enum CargoMessage {
+    CompilerArtifact(cargo_metadata::Artifact),
+    Diagnostic(Diagnostic),
+}
+
+#[derive(Deserialize)]
+#[serde(untagged)]
+enum JsonMessage {
+    Cargo(cargo_metadata::Message),
+    Rustc(Diagnostic),
+}
diff --git a/crates/hir_def/src/body/tests.rs b/crates/hir_def/src/body/tests.rs
index 63f5fe88d..3e8f16306 100644
--- a/crates/hir_def/src/body/tests.rs
+++ b/crates/hir_def/src/body/tests.rs
@@ -40,6 +40,14 @@ fn block_def_map_at(ra_fixture: &str) -> String {
     module.def_map(&db).dump(&db)
 }
 
+fn check_block_scopes_at(ra_fixture: &str, expect: Expect) {
+    let (db, position) = crate::test_db::TestDB::with_position(ra_fixture);
+
+    let module = db.module_at_position(position);
+    let actual = module.def_map(&db).dump_block_scopes(&db);
+    expect.assert_eq(&actual);
+}
+
 fn check_at(ra_fixture: &str, expect: Expect) {
     let actual = block_def_map_at(ra_fixture);
     expect.assert_eq(&actual);
diff --git a/crates/hir_def/src/body/tests/block.rs b/crates/hir_def/src/body/tests/block.rs
index 3b6ba4cde..bc3d0f138 100644
--- a/crates/hir_def/src/body/tests/block.rs
+++ b/crates/hir_def/src/body/tests/block.rs
@@ -134,6 +134,30 @@ struct Struct {}
 }
 
 #[test]
+fn nested_module_scoping() {
+    check_block_scopes_at(
+        r#"
+fn f() {
+    mod module {
+        struct Struct {}
+        fn f() {
+            use self::Struct;
+            $0
+        }
+    }
+}
+    "#,
+        expect![[r#"
+            BlockId(1) in ModuleId { krate: CrateId(0), block: Some(BlockId(0)), local_id: Idx::<ModuleData>(0) }
+            BlockId(0) in ModuleId { krate: CrateId(0), block: None, local_id: Idx::<ModuleData>(0) }
+            crate scope
+        "#]],
+    );
+    // FIXME: The module nesting here is wrong!
+    // The first block map should be located in module #1 (`mod module`), not #0 (BlockId(0) root module)
+}
+
+#[test]
 fn legacy_macro_items() {
     // Checks that legacy-scoped `macro_rules!` from parent namespaces are resolved and expanded
     // correctly.
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index 16a94a058..eaeca01bd 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -196,13 +196,6 @@ impl ItemTree {
         self.raw_attrs(of).clone().filter(db, krate)
     }
 
-    pub fn all_inner_items(&self) -> impl Iterator<Item = ModItem> + '_ {
-        match &self.data {
-            Some(data) => Some(data.inner_items.values().flatten().copied()).into_iter().flatten(),
-            None => None.into_iter().flatten(),
-        }
-    }
-
     pub fn inner_items_of_block(&self, block: FileAstId<ast::BlockExpr>) -> &[ModItem] {
         match &self.data {
             Some(data) => data.inner_items.get(&block).map(|it| &**it).unwrap_or(&[]),
diff --git a/crates/hir_def/src/nameres.rs b/crates/hir_def/src/nameres.rs
index 542f190a1..ba027c44a 100644
--- a/crates/hir_def/src/nameres.rs
+++ b/crates/hir_def/src/nameres.rs
@@ -410,6 +410,20 @@ impl DefMap {
         }
     }
 
+    pub fn dump_block_scopes(&self, db: &dyn DefDatabase) -> String {
+        let mut buf = String::new();
+        let mut arc;
+        let mut current_map = self;
+        while let Some(block) = &current_map.block {
+            format_to!(buf, "{:?} in {:?}\n", block.block, block.parent);
+            arc = block.parent.def_map(db);
+            current_map = &*arc;
+        }
+
+        format_to!(buf, "crate scope\n");
+        buf
+    }
+
     fn shrink_to_fit(&mut self) {
         // Exhaustive match to require handling new fields.
         let Self {
diff --git a/crates/hir_ty/Cargo.toml b/crates/hir_ty/Cargo.toml
index abc0e7532..66b3418f2 100644
--- a/crates/hir_ty/Cargo.toml
+++ b/crates/hir_ty/Cargo.toml
@@ -18,9 +18,9 @@ ena = "0.14.0"
 log = "0.4.8"
 rustc-hash = "1.1.0"
 scoped-tls = "1"
-chalk-solve = { version = "0.60", default-features = false }
-chalk-ir = "0.60"
-chalk-recursive = "0.60"
+chalk-solve = { version = "0.64", default-features = false }
+chalk-ir = "0.64"
+chalk-recursive = "0.64"
 la-arena = { version = "0.2.0", path = "../../lib/arena" }
 
 stdx = { path = "../stdx", version = "0.0.0" }
diff --git a/crates/ide_assists/src/handlers/fill_match_arms.rs b/crates/ide_assists/src/handlers/fill_match_arms.rs
index a30c4d04e..be927cc1c 100644
--- a/crates/ide_assists/src/handlers/fill_match_arms.rs
+++ b/crates/ide_assists/src/handlers/fill_match_arms.rs
@@ -53,7 +53,7 @@ pub(crate) fn fill_match_arms(acc: &mut Assists, ctx: &AssistContext) -> Option<
         .iter()
         .filter_map(ast::MatchArm::pat)
         .flat_map(|pat| match pat {
-            // Special casee OrPat as separate top-level pats
+            // Special case OrPat as separate top-level pats
             Pat::OrPat(or_pat) => Either::Left(or_pat.pats()),
             _ => Either::Right(iter::once(pat)),
         })
@@ -72,7 +72,11 @@ pub(crate) fn fill_match_arms(acc: &mut Assists, ctx: &AssistContext) -> Option<
             .filter(|variant_pat| is_variant_missing(&top_lvl_pats, variant_pat))
             .map(|pat| make::match_arm(iter::once(pat), make::expr_empty_block()))
             .collect::<Vec<_>>();
-        if Some(enum_def) == FamousDefs(&ctx.sema, Some(module.krate())).core_option_Option() {
+        if Some(enum_def)
+            == FamousDefs(&ctx.sema, Some(module.krate()))
+                .core_option_Option()
+                .map(|x| lift_enum(x))
+        {
             // Match `Some` variant first.
             cov_mark::hit!(option_order);
             variants.reverse()
@@ -151,49 +155,99 @@ fn does_pat_match_variant(pat: &Pat, var: &Pat) -> bool {
     }
 }
 
-fn resolve_enum_def(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> Option<hir::Enum> {
+#[derive(Eq, PartialEq, Clone)]
+enum ExtendedEnum {
+    Bool,
+    Enum(hir::Enum),
+}
+
+#[derive(Eq, PartialEq, Clone)]
+enum ExtendedVariant {
+    True,
+    False,
+    Variant(hir::Variant),
+}
+
+fn lift_enum(e: hir::Enum) -> ExtendedEnum {
+    ExtendedEnum::Enum(e)
+}
+
+impl ExtendedEnum {
+    fn variants(&self, db: &RootDatabase) -> Vec<ExtendedVariant> {
+        match self {
+            ExtendedEnum::Enum(e) => {
+                e.variants(db).into_iter().map(|x| ExtendedVariant::Variant(x)).collect::<Vec<_>>()
+            }
+            ExtendedEnum::Bool => {
+                Vec::<ExtendedVariant>::from([ExtendedVariant::True, ExtendedVariant::False])
+            }
+        }
+    }
+}
+
+fn resolve_enum_def(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> Option<ExtendedEnum> {
     sema.type_of_expr(&expr)?.autoderef(sema.db).find_map(|ty| match ty.as_adt() {
-        Some(Adt::Enum(e)) => Some(e),
-        _ => None,
+        Some(Adt::Enum(e)) => Some(ExtendedEnum::Enum(e)),
+        _ => {
+            if ty.is_bool() {
+                Some(ExtendedEnum::Bool)
+            } else {
+                None
+            }
+        }
     })
 }
 
 fn resolve_tuple_of_enum_def(
     sema: &Semantics<RootDatabase>,
     expr: &ast::Expr,
-) -> Option<Vec<hir::Enum>> {
+) -> Option<Vec<ExtendedEnum>> {
     sema.type_of_expr(&expr)?
         .tuple_fields(sema.db)
         .iter()
         .map(|ty| {
             ty.autoderef(sema.db).find_map(|ty| match ty.as_adt() {
-                Some(Adt::Enum(e)) => Some(e),
+                Some(Adt::Enum(e)) => Some(lift_enum(e)),
                 // For now we only handle expansion for a tuple of enums. Here
                 // we map non-enum items to None and rely on `collect` to
                 // convert Vec<Option<hir::Enum>> into Option<Vec<hir::Enum>>.
-                _ => None,
+                _ => {
+                    if ty.is_bool() {
+                        Some(ExtendedEnum::Bool)
+                    } else {
+                        None
+                    }
+                }
             })
         })
         .collect()
 }
 
-fn build_pat(db: &RootDatabase, module: hir::Module, var: hir::Variant) -> Option<ast::Pat> {
-    let path = mod_path_to_ast(&module.find_use_path(db, ModuleDef::from(var))?);
+fn build_pat(db: &RootDatabase, module: hir::Module, var: ExtendedVariant) -> Option<ast::Pat> {
+    match var {
+        ExtendedVariant::Variant(var) => {
+            let path = mod_path_to_ast(&module.find_use_path(db, ModuleDef::from(var))?);
+
+            // FIXME: use HIR for this; it doesn't currently expose struct vs. tuple vs. unit variants though
+            let pat: ast::Pat = match var.source(db)?.value.kind() {
+                ast::StructKind::Tuple(field_list) => {
+                    let pats =
+                        iter::repeat(make::wildcard_pat().into()).take(field_list.fields().count());
+                    make::tuple_struct_pat(path, pats).into()
+                }
+                ast::StructKind::Record(field_list) => {
+                    let pats =
+                        field_list.fields().map(|f| make::ident_pat(f.name().unwrap()).into());
+                    make::record_pat(path, pats).into()
+                }
+                ast::StructKind::Unit => make::path_pat(path),
+            };
 
-    // FIXME: use HIR for this; it doesn't currently expose struct vs. tuple vs. unit variants though
-    let pat: ast::Pat = match var.source(db)?.value.kind() {
-        ast::StructKind::Tuple(field_list) => {
-            let pats = iter::repeat(make::wildcard_pat().into()).take(field_list.fields().count());
-            make::tuple_struct_pat(path, pats).into()
-        }
-        ast::StructKind::Record(field_list) => {
-            let pats = field_list.fields().map(|f| make::ident_pat(f.name().unwrap()).into());
-            make::record_pat(path, pats).into()
+            Some(pat)
         }
-        ast::StructKind::Unit => make::path_pat(path),
-    };
-
-    Some(pat)
+        ExtendedVariant::True => Some(ast::Pat::from(make::literal_pat("true"))),
+        ExtendedVariant::False => Some(ast::Pat::from(make::literal_pat("false"))),
+    }
 }
 
 #[cfg(test)]
@@ -226,6 +280,21 @@ mod tests {
     }
 
     #[test]
+    fn all_boolean_match_arms_provided() {
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            fn foo(a: bool) {
+                match a$0 {
+                    true => {}
+                    false => {}
+                }
+            }
+            "#,
+        )
+    }
+
+    #[test]
     fn tuple_of_non_enum() {
         // for now this case is not handled, although it potentially could be
         // in the future
@@ -241,6 +310,113 @@ mod tests {
     }
 
     #[test]
+    fn fill_match_arms_boolean() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            fn foo(a: bool) {
+                match a$0 {
+                }
+            }
+            "#,
+            r#"
+            fn foo(a: bool) {
+                match a {
+                    $0true => {}
+                    false => {}
+                }
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn partial_fill_boolean() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            fn foo(a: bool) {
+                match a$0 {
+                    true => {}
+                }
+            }
+            "#,
+            r#"
+            fn foo(a: bool) {
+                match a {
+                    true => {}
+                    $0false => {}
+                }
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn all_boolean_tuple_arms_provided() {
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            fn foo(a: bool) {
+                match (a, a)$0 {
+                    (true, true) => {}
+                    (true, false) => {}
+                    (false, true) => {}
+                    (false, false) => {}
+                }
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn fill_boolean_tuple() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            fn foo(a: bool) {
+                match (a, a)$0 {
+                }
+            }
+            "#,
+            r#"
+            fn foo(a: bool) {
+                match (a, a) {
+                    $0(true, true) => {}
+                    (true, false) => {}
+                    (false, true) => {}
+                    (false, false) => {}
+                }
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn partial_fill_boolean_tuple() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            fn foo(a: bool) {
+                match (a, a)$0 {
+                    (false, true) => {}
+                }
+            }
+            "#,
+            r#"
+            fn foo(a: bool) {
+                match (a, a) {
+                    (false, true) => {}
+                    $0(true, true) => {}
+                    (true, false) => {}
+                    (false, false) => {}
+                }
+            }
+            "#,
+        )
+    }
+
+    #[test]
     fn partial_fill_record_tuple() {
         check_assist(
             fill_match_arms,
diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index 7ddea22c8..1109d2daf 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -17,7 +17,7 @@ use ide_db::helpers::{
 };
 use lsp_types::{ClientCapabilities, MarkupKind};
 use project_model::{CargoConfig, ProjectJson, ProjectJsonData, ProjectManifest, RustcSource};
-use rustc_hash::FxHashSet;
+use rustc_hash::{FxHashMap, FxHashSet};
 use serde::{de::DeserializeOwned, Deserialize};
 use vfs::AbsPathBuf;
 
@@ -99,6 +99,9 @@ config_data! {
         diagnostics_enableExperimental: bool    = "true",
         /// List of rust-analyzer diagnostics to disable.
         diagnostics_disabled: FxHashSet<String> = "[]",
+        /// Map of prefixes to be substituted when parsing diagnostic file paths.
+        /// This should be the reverse mapping of what is passed to `rustc` as `--remap-path-prefix`.
+        diagnostics_remapPrefix: FxHashMap<String, String> = "{}",
         /// List of warnings that should be displayed with info severity.
         ///
         /// The warnings will be indicated by a blue squiggly underline in code
@@ -474,6 +477,7 @@ impl Config {
     }
     pub fn diagnostics_map(&self) -> DiagnosticsMapConfig {
         DiagnosticsMapConfig {
+            remap_prefix: self.data.diagnostics_remapPrefix.clone(),
             warnings_as_info: self.data.diagnostics_warningsAsInfo.clone(),
             warnings_as_hint: self.data.diagnostics_warningsAsHint.clone(),
         }
@@ -835,6 +839,9 @@ fn field_props(field: &str, ty: &str, doc: &[&str], default: &str) -> serde_json
             "items": { "type": "string" },
             "uniqueItems": true,
         },
+        "FxHashMap<String, String>" => set! {
+            "type": "object",
+        },
         "Option<usize>" => set! {
             "type": ["null", "integer"],
             "minimum": 0,
diff --git a/crates/rust-analyzer/src/diagnostics.rs b/crates/rust-analyzer/src/diagnostics.rs
index f01548c50..d4b9db362 100644
--- a/crates/rust-analyzer/src/diagnostics.rs
+++ b/crates/rust-analyzer/src/diagnostics.rs
@@ -12,6 +12,7 @@ pub(crate) type CheckFixes = Arc<FxHashMap<FileId, Vec<Fix>>>;
 
 #[derive(Debug, Default, Clone)]
 pub struct DiagnosticsMapConfig {
+    pub remap_prefix: FxHashMap<String, String>,
     pub warnings_as_info: Vec<String>,
     pub warnings_as_hint: Vec<String>,
 }
diff --git a/crates/rust-analyzer/src/diagnostics/to_proto.rs b/crates/rust-analyzer/src/diagnostics/to_proto.rs
index ca18997e4..82dd0da9a 100644
--- a/crates/rust-analyzer/src/diagnostics/to_proto.rs
+++ b/crates/rust-analyzer/src/diagnostics/to_proto.rs
@@ -1,6 +1,9 @@
 //! This module provides the functionality needed to convert diagnostics from
 //! `cargo check` json format to the LSP diagnostic format.
-use std::{collections::HashMap, path::Path};
+use std::{
+    collections::HashMap,
+    path::{Path, PathBuf},
+};
 
 use flycheck::{DiagnosticLevel, DiagnosticSpan};
 use stdx::format_to;
@@ -41,8 +44,12 @@ fn is_dummy_macro_file(file_name: &str) -> bool {
 }
 
 /// Converts a Rust span to a LSP location
-fn location(workspace_root: &Path, span: &DiagnosticSpan) -> lsp_types::Location {
-    let file_name = workspace_root.join(&span.file_name);
+fn location(
+    config: &DiagnosticsMapConfig,
+    workspace_root: &Path,
+    span: &DiagnosticSpan,
+) -> lsp_types::Location {
+    let file_name = resolve_path(config, workspace_root, &span.file_name);
     let uri = url_from_abs_path(&file_name);
 
     // FIXME: this doesn't handle UTF16 offsets correctly
@@ -58,32 +65,50 @@ fn location(workspace_root: &Path, span: &DiagnosticSpan) -> lsp_types::Location
 ///
 /// This takes locations pointing into the standard library, or generally outside the current
 /// workspace into account and tries to avoid those, in case macros are involved.
-fn primary_location(workspace_root: &Path, span: &DiagnosticSpan) -> lsp_types::Location {
+fn primary_location(
+    config: &DiagnosticsMapConfig,
+    workspace_root: &Path,
+    span: &DiagnosticSpan,
+) -> lsp_types::Location {
     let span_stack = std::iter::successors(Some(span), |span| Some(&span.expansion.as_ref()?.span));
     for span in span_stack.clone() {
-        let abs_path = workspace_root.join(&span.file_name);
+        let abs_path = resolve_path(config, workspace_root, &span.file_name);
         if !is_dummy_macro_file(&span.file_name) && abs_path.starts_with(workspace_root) {
-            return location(workspace_root, span);
+            return location(config, workspace_root, span);
         }
     }
 
     // Fall back to the outermost macro invocation if no suitable span comes up.
     let last_span = span_stack.last().unwrap();
-    location(workspace_root, last_span)
+    location(config, workspace_root, last_span)
 }
 
 /// Converts a secondary Rust span to a LSP related information
 ///
 /// If the span is unlabelled this will return `None`.
 fn diagnostic_related_information(
+    config: &DiagnosticsMapConfig,
     workspace_root: &Path,
     span: &DiagnosticSpan,
 ) -> Option<lsp_types::DiagnosticRelatedInformation> {
     let message = span.label.clone()?;
-    let location = location(workspace_root, span);
+    let location = location(config, workspace_root, span);
     Some(lsp_types::DiagnosticRelatedInformation { location, message })
 }
 
+/// Resolves paths applying any matching path prefix remappings, and then
+/// joining the path to the workspace root.
+fn resolve_path(config: &DiagnosticsMapConfig, workspace_root: &Path, file_name: &str) -> PathBuf {
+    match config
+        .remap_prefix
+        .iter()
+        .find_map(|(from, to)| file_name.strip_prefix(from).map(|file_name| (to, file_name)))
+    {
+        Some((to, file_name)) => workspace_root.join(format!("{}{}", to, file_name)),
+        None => workspace_root.join(file_name),
+    }
+}
+
 struct SubDiagnostic {
     related: lsp_types::DiagnosticRelatedInformation,
     suggested_fix: Option<lsp_ext::CodeAction>,
@@ -95,6 +120,7 @@ enum MappedRustChildDiagnostic {
 }
 
 fn map_rust_child_diagnostic(
+    config: &DiagnosticsMapConfig,
     workspace_root: &Path,
     rd: &flycheck::Diagnostic,
 ) -> MappedRustChildDiagnostic {
@@ -108,7 +134,7 @@ fn map_rust_child_diagnostic(
     let mut edit_map: HashMap<lsp_types::Url, Vec<lsp_types::TextEdit>> = HashMap::new();
     for &span in &spans {
         if let Some(suggested_replacement) = &span.suggested_replacement {
-            let location = location(workspace_root, span);
+            let location = location(config, workspace_root, span);
             let edit = lsp_types::TextEdit::new(location.range, suggested_replacement.clone());
             edit_map.entry(location.uri).or_default().push(edit);
         }
@@ -117,7 +143,7 @@ fn map_rust_child_diagnostic(
     if edit_map.is_empty() {
         MappedRustChildDiagnostic::SubDiagnostic(SubDiagnostic {
             related: lsp_types::DiagnosticRelatedInformation {
-                location: location(workspace_root, spans[0]),
+                location: location(config, workspace_root, spans[0]),
                 message: rd.message.clone(),
             },
             suggested_fix: None,
@@ -125,7 +151,7 @@ fn map_rust_child_diagnostic(
     } else {
         MappedRustChildDiagnostic::SubDiagnostic(SubDiagnostic {
             related: lsp_types::DiagnosticRelatedInformation {
-                location: location(workspace_root, spans[0]),
+                location: location(config, workspace_root, spans[0]),
                 message: rd.message.clone(),
             },
             suggested_fix: Some(lsp_ext::CodeAction {
@@ -190,7 +216,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
     let mut tags = Vec::new();
 
     for secondary_span in rd.spans.iter().filter(|s| !s.is_primary) {
-        let related = diagnostic_related_information(workspace_root, secondary_span);
+        let related = diagnostic_related_information(config, workspace_root, secondary_span);
         if let Some(related) = related {
             subdiagnostics.push(SubDiagnostic { related, suggested_fix: None });
         }
@@ -198,7 +224,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
 
     let mut message = rd.message.clone();
     for child in &rd.children {
-        let child = map_rust_child_diagnostic(workspace_root, &child);
+        let child = map_rust_child_diagnostic(config, workspace_root, &child);
         match child {
             MappedRustChildDiagnostic::SubDiagnostic(sub) => {
                 subdiagnostics.push(sub);
@@ -242,7 +268,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
     primary_spans
         .iter()
         .flat_map(|primary_span| {
-            let primary_location = primary_location(workspace_root, &primary_span);
+            let primary_location = primary_location(config, workspace_root, &primary_span);
 
             let mut message = message.clone();
             if needs_primary_span_label {
@@ -272,7 +298,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
                 // generated that code.
                 let is_in_macro_call = i != 0;
 
-                let secondary_location = location(workspace_root, &span);
+                let secondary_location = location(config, workspace_root, &span);
                 if secondary_location == primary_location {
                     continue;
                 }
diff --git a/crates/syntax/Cargo.toml b/crates/syntax/Cargo.toml
index a8c1a8075..556f80882 100644
--- a/crates/syntax/Cargo.toml
+++ b/crates/syntax/Cargo.toml
@@ -14,7 +14,7 @@ doctest = false
 cov-mark = { version = "1.1", features = ["thread-local"] }
 itertools = "0.10.0"
 rowan = "=0.13.0-pre.3"
-rustc_lexer = { version = "714.0.0", package = "rustc-ap-rustc_lexer" }
+rustc_lexer = { version = "716.0.0", package = "rustc-ap-rustc_lexer" }
 rustc-hash = "1.1.0"
 arrayvec = "0.7"
 once_cell = "1.3.1"
diff --git a/crates/syntax/src/ast/make.rs b/crates/syntax/src/ast/make.rs
index 94d4f2cf0..4cf6f871e 100644
--- a/crates/syntax/src/ast/make.rs
+++ b/crates/syntax/src/ast/make.rs
@@ -294,6 +294,14 @@ pub fn wildcard_pat() -> ast::WildcardPat {
     }
 }
 
+pub fn literal_pat(lit: &str) -> ast::LiteralPat {
+    return from_text(lit);
+
+    fn from_text(text: &str) -> ast::LiteralPat {
+        ast_from_text(&format!("fn f() {{ match x {{ {} => {{}} }} }}", text))
+    }
+}
+
 /// Creates a tuple of patterns from an iterator of patterns.
 ///
 /// Invariant: `pats` must be length > 0
diff --git a/docs/user/generated_config.adoc b/docs/user/generated_config.adoc
index e0ee35b4e..e28423e99 100644
--- a/docs/user/generated_config.adoc
+++ b/docs/user/generated_config.adoc
@@ -147,6 +147,12 @@ have more false positives than usual.
 --
 List of rust-analyzer diagnostics to disable.
 --
+[[rust-analyzer.diagnostics.remapPrefix]]rust-analyzer.diagnostics.remapPrefix (default: `{}`)::
++
+--
+Map of prefixes to be substituted when parsing diagnostic file paths.
+This should be the reverse mapping of what is passed to `rustc` as `--remap-path-prefix`.
+--
 [[rust-analyzer.diagnostics.warningsAsHint]]rust-analyzer.diagnostics.warningsAsHint (default: `[]`)::
 +
 --
diff --git a/editors/code/package.json b/editors/code/package.json
index 06ed62d8d..fa5632f90 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -565,6 +565,11 @@
                     },
                     "uniqueItems": true
                 },
+                "rust-analyzer.diagnostics.remapPrefix": {
+                    "markdownDescription": "Map of prefixes to be substituted when parsing diagnostic file paths.\nThis should be the reverse mapping of what is passed to `rustc` as `--remap-path-prefix`.",
+                    "default": {},
+                    "type": "object"
+                },
                 "rust-analyzer.diagnostics.warningsAsHint": {
                     "markdownDescription": "List of warnings that should be displayed with info severity.\n\nThe warnings will be indicated by a blue squiggly underline in code\nand a blue icon in the `Problems Panel`.",
                     "default": [],
@@ -1195,4 +1200,4 @@
             ]
         }
     }
-}
\ No newline at end of file
+}