15 files changed, 609 insertions, 96 deletions

diff --git a/crates/ra_db/src/input.rs b/crates/ra_db/src/input.rs
index a5f4e489f..c103503bd 100644
--- a/crates/ra_db/src/input.rs
+++ b/crates/ra_db/src/input.rs
@@ -31,9 +31,23 @@ pub struct SourceRootId(pub u32);
 
 #[derive(Default, Clone, Debug, PartialEq, Eq)]
 pub struct SourceRoot {
+    /// Sysroot or crates.io library.
+    ///
+    /// Libraries are considered mostly immutable, this assumption is used to
+    /// optimize salsa's query structure
+    pub is_library: bool,
     pub files: FxHashMap<RelativePathBuf, FileId>,
 }
 
+impl SourceRoot {
+    pub fn new() -> SourceRoot {
+        Default::default()
+    }
+    pub fn new_library() -> SourceRoot {
+        SourceRoot { is_library: true, ..SourceRoot::new() }
+    }
+}
+
 /// `CrateGraph` is a bit of information which turns a set of text files into a
 /// number of Rust crates. Each crate is defined by the `FileId` of its root module,
 /// the set of cfg flags (not yet implemented) and the set of dependencies. Note
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index 46ec136bd..e023ff25a 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -4,6 +4,7 @@
 //! and the corresponding code mostly in librustc_typeck/check/method/probe.rs.
 use std::sync::Arc;
 
+use arrayvec::ArrayVec;
 use rustc_hash::FxHashMap;
 
 use crate::{
@@ -113,19 +114,32 @@ impl CrateImplBlocks {
     }
 }
 
-fn def_crate(db: &impl HirDatabase, cur_crate: Crate, ty: &Ty) -> Option<Crate> {
+fn def_crates(db: &impl HirDatabase, cur_crate: Crate, ty: &Ty) -> Option<ArrayVec<[Crate; 2]>> {
+    // Types like slice can have inherent impls in several crates, (core and alloc).
+    // The correspoinding impls are marked with lang items, so we can use them to find the required crates.
+    macro_rules! lang_item_crate {
+        ($db:expr, $cur_crate:expr, $($name:expr),+ $(,)?) => {{
+            let mut v = ArrayVec::<[Crate; 2]>::new();
+            $(
+                v.push($db.lang_item($cur_crate, $name.into())?.krate($db)?);
+            )+
+            Some(v)
+        }};
+    }
+
     match ty {
         Ty::Apply(a_ty) => match a_ty.ctor {
-            TypeCtor::Adt(def_id) => def_id.krate(db),
-            TypeCtor::Bool => db.lang_item(cur_crate, "bool".into())?.krate(db),
-            TypeCtor::Char => db.lang_item(cur_crate, "char".into())?.krate(db),
+            TypeCtor::Adt(def_id) => Some(std::iter::once(def_id.krate(db)?).collect()),
+            TypeCtor::Bool => lang_item_crate!(db, cur_crate, "bool"),
+            TypeCtor::Char => lang_item_crate!(db, cur_crate, "char"),
             TypeCtor::Float(UncertainFloatTy::Known(f)) => {
-                db.lang_item(cur_crate, f.ty_to_string().into())?.krate(db)
+                lang_item_crate!(db, cur_crate, f.ty_to_string())
             }
             TypeCtor::Int(UncertainIntTy::Known(i)) => {
-                db.lang_item(cur_crate, i.ty_to_string().into())?.krate(db)
+                lang_item_crate!(db, cur_crate, i.ty_to_string())
             }
-            TypeCtor::Str => db.lang_item(cur_crate, "str".into())?.krate(db),
+            TypeCtor::Str => lang_item_crate!(db, cur_crate, "str"),
+            TypeCtor::Slice => lang_item_crate!(db, cur_crate, "slice_alloc", "slice"),
             _ => None,
         },
         _ => None,
@@ -218,19 +232,17 @@ fn iterate_inherent_methods<T>(
     krate: Crate,
     mut callback: impl FnMut(&Ty, Function) -> Option<T>,
 ) -> Option<T> {
-    let krate = match def_crate(db, krate, &ty.value) {
-        Some(krate) => krate,
-        None => return None,
-    };
-    let impls = db.impls_in_crate(krate);
+    for krate in def_crates(db, krate, &ty.value)? {
+        let impls = db.impls_in_crate(krate);
 
-    for impl_block in impls.lookup_impl_blocks(&ty.value) {
-        for item in impl_block.items(db) {
-            if let ImplItem::Method(f) = item {
-                let data = f.data(db);
-                if name.map_or(true, |name| data.name() == name) && data.has_self_param() {
-                    if let Some(result) = callback(&ty.value, f) {
-                        return Some(result);
+        for impl_block in impls.lookup_impl_blocks(&ty.value) {
+            for item in impl_block.items(db) {
+                if let ImplItem::Method(f) = item {
+                    let data = f.data(db);
+                    if name.map_or(true, |name| data.name() == name) && data.has_self_param() {
+                        if let Some(result) = callback(&ty.value, f) {
+                            return Some(result);
+                        }
                     }
                 }
             }
@@ -248,13 +260,14 @@ impl Ty {
         krate: Crate,
         mut callback: impl FnMut(ImplItem) -> Option<T>,
     ) -> Option<T> {
-        let krate = def_crate(db, krate, &self)?;
-        let impls = db.impls_in_crate(krate);
+        for krate in def_crates(db, krate, &self)? {
+            let impls = db.impls_in_crate(krate);
 
-        for impl_block in impls.lookup_impl_blocks(&self) {
-            for item in impl_block.items(db) {
-                if let Some(result) = callback(item) {
-                    return Some(result);
+            for impl_block in impls.lookup_impl_blocks(&self) {
+                for item in impl_block.items(db) {
+                    if let Some(result) = callback(item) {
+                        return Some(result);
+                    }
                 }
             }
         }
diff --git a/crates/ra_ide_api/src/change.rs b/crates/ra_ide_api/src/change.rs
index 895b1e966..8d9918d16 100644
--- a/crates/ra_ide_api/src/change.rs
+++ b/crates/ra_ide_api/src/change.rs
@@ -163,7 +163,8 @@ impl RootDatabase {
         if !change.new_roots.is_empty() {
             let mut local_roots = Vec::clone(&self.local_roots());
             for (root_id, is_local) in change.new_roots {
-                self.set_source_root(root_id, Default::default());
+                let root = if is_local { SourceRoot::new() } else { SourceRoot::new_library() };
+                self.set_source_root(root_id, Arc::new(root));
                 if is_local {
                     local_roots.push(root_id);
                 }
diff --git a/crates/ra_ide_api/src/completion/complete_postfix.rs b/crates/ra_ide_api/src/completion/complete_postfix.rs
index 278b1b797..e20a12e2a 100644
--- a/crates/ra_ide_api/src/completion/complete_postfix.rs
+++ b/crates/ra_ide_api/src/completion/complete_postfix.rs
@@ -51,6 +51,8 @@ pub(super) fn complete_postfix(acc: &mut Completions, ctx: &CompletionContext) {
         )
         .add_to(acc);
         postfix_snippet(ctx, "dbg", "dbg!(expr)", &format!("dbg!({})", receiver_text)).add_to(acc);
+        postfix_snippet(ctx, "box", "Box::new(expr)", &format!("Box::new({})", receiver_text))
+            .add_to(acc);
     }
 }
 
diff --git a/crates/ra_ide_api/src/completion/snapshots/completion_item__postfix_completion_works_for_trivial_path_expression.snap b/crates/ra_ide_api/src/completion/snapshots/completion_item__postfix_completion_works_for_trivial_path_expression.snap
index fcb292596..c1a40b7b4 100644
--- a/crates/ra_ide_api/src/completion/snapshots/completion_item__postfix_completion_works_for_trivial_path_expression.snap
+++ b/crates/ra_ide_api/src/completion/snapshots/completion_item__postfix_completion_works_for_trivial_path_expression.snap
@@ -1,11 +1,18 @@
 ---
-created: "2019-05-23T22:23:35.118738523Z"
+created: "2019-06-23T13:01:08.775536006Z"
 creator: [email protected]
 source: crates/ra_ide_api/src/completion/completion_item.rs
 expression: kind_completions
 ---
 [
     CompletionItem {
+        label: "box",
+        source_range: [76; 76),
+        delete: [72; 76),
+        insert: "Box::new(bar)",
+        detail: "Box::new(expr)",
+    },
+    CompletionItem {
         label: "dbg",
         source_range: [76; 76),
         delete: [72; 76),
diff --git a/crates/ra_parser/src/grammar/items.rs b/crates/ra_parser/src/grammar/items.rs
index e85147e9e..424d0476d 100644
--- a/crates/ra_parser/src/grammar/items.rs
+++ b/crates/ra_parser/src/grammar/items.rs
@@ -103,7 +103,21 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker, flavor: ItemFlavor) -> Resul
         p.bump_remap(T![auto]);
         has_mods = true;
     }
-    if p.at(IDENT) && p.at_contextual_kw("default") && p.nth(1) == T![impl] {
+
+    if p.at(IDENT)
+        && p.at_contextual_kw("default")
+        && (match p.nth(1) {
+            T![impl] => true,
+            T![fn] | T![type] => {
+                if let ItemFlavor::Mod = flavor {
+                    true
+                } else {
+                    false
+                }
+            }
+            _ => false,
+        })
+    {
         p.bump_remap(T![default]);
         has_mods = true;
     }
@@ -163,12 +177,25 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker, flavor: ItemFlavor) -> Resul
         // test default_impl
         // default impl Foo {}
 
+        // test_err default_fn_type
+        // trait T {
+        //     default type T = Bar;
+        //     default fn foo() {}
+        // }
+
+        // test default_fn_type
+        // impl T for Foo {
+        //     default type T = Bar;
+        //     default fn foo() {}
+        // }
+
         // test unsafe_default_impl
         // unsafe default impl Foo {}
         T![impl] => {
             traits::impl_block(p);
             m.complete(p, IMPL_BLOCK);
         }
+
         // test existential_type
         // existential type Foo: Fn() -> usize;
         T![type] => {
diff --git a/crates/ra_syntax/tests/data/parser/inline/err/0014_default_fn_type.rs b/crates/ra_syntax/tests/data/parser/inline/err/0014_default_fn_type.rs
new file mode 100644
index 000000000..15ba8f4a8
--- /dev/null
+++ b/crates/ra_syntax/tests/data/parser/inline/err/0014_default_fn_type.rs
@@ -0,0 +1,4 @@
+trait T {
+    default type T = Bar;
+    default fn foo() {}
+}
diff --git a/crates/ra_syntax/tests/data/parser/inline/err/0014_default_fn_type.txt b/crates/ra_syntax/tests/data/parser/inline/err/0014_default_fn_type.txt
new file mode 100644
index 000000000..7da4e243f
--- /dev/null
+++ b/crates/ra_syntax/tests/data/parser/inline/err/0014_default_fn_type.txt
@@ -0,0 +1,58 @@
+SOURCE_FILE@[0; 62)
+  TRAIT_DEF@[0; 61)
+    TRAIT_KW@[0; 5) "trait"
+    WHITESPACE@[5; 6) " "
+    NAME@[6; 7)
+      IDENT@[6; 7) "T"
+    WHITESPACE@[7; 8) " "
+    ITEM_LIST@[8; 61)
+      L_CURLY@[8; 9) "{"
+      WHITESPACE@[9; 14) "\n    "
+      MACRO_CALL@[14; 21)
+        PATH@[14; 21)
+          PATH_SEGMENT@[14; 21)
+            NAME_REF@[14; 21)
+              IDENT@[14; 21) "default"
+      WHITESPACE@[21; 22) " "
+      TYPE_ALIAS_DEF@[22; 35)
+        TYPE_KW@[22; 26) "type"
+        WHITESPACE@[26; 27) " "
+        NAME@[27; 28)
+          IDENT@[27; 28) "T"
+        WHITESPACE@[28; 29) " "
+        EQ@[29; 30) "="
+        WHITESPACE@[30; 31) " "
+        PATH_TYPE@[31; 34)
+          PATH@[31; 34)
+            PATH_SEGMENT@[31; 34)
+              NAME_REF@[31; 34)
+                IDENT@[31; 34) "Bar"
+        SEMI@[34; 35) ";"
+      WHITESPACE@[35; 40) "\n    "
+      MACRO_CALL@[40; 47)
+        PATH@[40; 47)
+          PATH_SEGMENT@[40; 47)
+            NAME_REF@[40; 47)
+              IDENT@[40; 47) "default"
+      WHITESPACE@[47; 48) " "
+      FN_DEF@[48; 59)
+        FN_KW@[48; 50) "fn"
+        WHITESPACE@[50; 51) " "
+        NAME@[51; 54)
+          IDENT@[51; 54) "foo"
+        PARAM_LIST@[54; 56)
+          L_PAREN@[54; 55) "("
+          R_PAREN@[55; 56) ")"
+        WHITESPACE@[56; 57) " "
+        BLOCK@[57; 59)
+          L_CURLY@[57; 58) "{"
+          R_CURLY@[58; 59) "}"
+      WHITESPACE@[59; 60) "\n"
+      R_CURLY@[60; 61) "}"
+  WHITESPACE@[61; 62) "\n"
+error 21: expected EXCL
+error 21: expected `{`, `[`, `(`
+error 21: expected SEMI
+error 47: expected EXCL
+error 47: expected `{`, `[`, `(`
+error 47: expected SEMI
diff --git a/crates/ra_syntax/tests/data/parser/inline/ok/0132_default_fn_type.rs b/crates/ra_syntax/tests/data/parser/inline/ok/0132_default_fn_type.rs
new file mode 100644
index 000000000..8f5d61113
--- /dev/null
+++ b/crates/ra_syntax/tests/data/parser/inline/ok/0132_default_fn_type.rs
@@ -0,0 +1,4 @@
+impl T for Foo {
+    default type T = Bar;
+    default fn foo() {}
+}
diff --git a/crates/ra_syntax/tests/data/parser/inline/ok/0132_default_fn_type.txt b/crates/ra_syntax/tests/data/parser/inline/ok/0132_default_fn_type.txt
new file mode 100644
index 000000000..384b203d3
--- /dev/null
+++ b/crates/ra_syntax/tests/data/parser/inline/ok/0132_default_fn_type.txt
@@ -0,0 +1,55 @@
+SOURCE_FILE@[0; 69)
+  IMPL_BLOCK@[0; 68)
+    IMPL_KW@[0; 4) "impl"
+    WHITESPACE@[4; 5) " "
+    PATH_TYPE@[5; 6)
+      PATH@[5; 6)
+        PATH_SEGMENT@[5; 6)
+          NAME_REF@[5; 6)
+            IDENT@[5; 6) "T"
+    WHITESPACE@[6; 7) " "
+    FOR_KW@[7; 10) "for"
+    WHITESPACE@[10; 11) " "
+    PATH_TYPE@[11; 14)
+      PATH@[11; 14)
+        PATH_SEGMENT@[11; 14)
+          NAME_REF@[11; 14)
+            IDENT@[11; 14) "Foo"
+    WHITESPACE@[14; 15) " "
+    ITEM_LIST@[15; 68)
+      L_CURLY@[15; 16) "{"
+      WHITESPACE@[16; 21) "\n    "
+      TYPE_ALIAS_DEF@[21; 42)
+        DEFAULT_KW@[21; 28) "default"
+        WHITESPACE@[28; 29) " "
+        TYPE_KW@[29; 33) "type"
+        WHITESPACE@[33; 34) " "
+        NAME@[34; 35)
+          IDENT@[34; 35) "T"
+        WHITESPACE@[35; 36) " "
+        EQ@[36; 37) "="
+        WHITESPACE@[37; 38) " "
+        PATH_TYPE@[38; 41)
+          PATH@[38; 41)
+            PATH_SEGMENT@[38; 41)
+              NAME_REF@[38; 41)
+                IDENT@[38; 41) "Bar"
+        SEMI@[41; 42) ";"
+      WHITESPACE@[42; 47) "\n    "
+      FN_DEF@[47; 66)
+        DEFAULT_KW@[47; 54) "default"
+        WHITESPACE@[54; 55) " "
+        FN_KW@[55; 57) "fn"
+        WHITESPACE@[57; 58) " "
+        NAME@[58; 61)
+          IDENT@[58; 61) "foo"
+        PARAM_LIST@[61; 63)
+          L_PAREN@[61; 62) "("
+          R_PAREN@[62; 63) ")"
+        WHITESPACE@[63; 64) " "
+        BLOCK@[64; 66)
+          L_CURLY@[64; 65) "{"
+          R_CURLY@[65; 66) "}"
+      WHITESPACE@[66; 67) "\n"
+      R_CURLY@[67; 68) "}"
+  WHITESPACE@[68; 69) "\n"
diff --git a/editors/code/package.json b/editors/code/package.json
index c2ed8d126..ac2ba82e3 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -201,11 +201,16 @@
                     ],
                     "description": "Whether to run `cargo watch` on startup"
                 },
-                "rust-analyzer.cargo-watch.check-arguments": {
+                "rust-analyzer.cargo-watch.arguments": {
                     "type": "string",
-                    "description": "`cargo-watch` check arguments. (e.g: `--features=\"shumway,pdf\"` will run as `cargo watch -x \"check --features=\"shumway,pdf\"\"` )",
+                    "description": "`cargo-watch` arguments. (e.g: `--features=\"shumway,pdf\"` will run as `cargo watch -x \"check --features=\"shumway,pdf\"\"` )",
                     "default": ""
                 },
+                "rust-analyzer.cargo-watch.command": {
+                    "type": "string",
+                    "description": "`cargo-watch` command. (e.g: `clippy` will run as `cargo watch -x clippy` )",
+                    "default": "check"
+                },
                 "rust-analyzer.trace.server": {
                     "type": "string",
                     "scope": "window",
diff --git a/editors/code/src/commands/cargo_watch.ts b/editors/code/src/commands/cargo_watch.ts
index 6ba794bb3..126a8b1b3 100644
--- a/editors/code/src/commands/cargo_watch.ts
+++ b/editors/code/src/commands/cargo_watch.ts
@@ -4,6 +4,10 @@ import * as path from 'path';
 import * as vscode from 'vscode';
 import { Server } from '../server';
 import { terminate } from '../utils/processes';
+import {
+    mapRustDiagnosticToVsCode,
+    RustDiagnostic
+} from '../utils/rust_diagnostics';
 import { LineBuffer } from './line_buffer';
 import { StatusDisplay } from './watch_status';
 
@@ -33,20 +37,39 @@ export function registerCargoWatchProvider(
     return provider;
 }
 
-export class CargoWatchProvider implements vscode.Disposable {
+export class CargoWatchProvider
+    implements vscode.Disposable, vscode.CodeActionProvider {
     private readonly diagnosticCollection: vscode.DiagnosticCollection;
     private readonly statusDisplay: StatusDisplay;
     private readonly outputChannel: vscode.OutputChannel;
+
+    private codeActions: {
+        [fileUri: string]: vscode.CodeAction[];
+    };
+    private readonly codeActionDispose: vscode.Disposable;
+
     private cargoProcess?: child_process.ChildProcess;
 
     constructor() {
         this.diagnosticCollection = vscode.languages.createDiagnosticCollection(
             'rustc'
         );
-        this.statusDisplay = new StatusDisplay();
+        this.statusDisplay = new StatusDisplay(
+            Server.config.cargoWatchOptions.command
+        );
         this.outputChannel = vscode.window.createOutputChannel(
             'Cargo Watch Trace'
         );
+
+        // Register code actions for rustc's suggested fixes
+        this.codeActions = {};
+        this.codeActionDispose = vscode.languages.registerCodeActionsProvider(
+            [{ scheme: 'file', language: 'rust' }],
+            this,
+            {
+                providedCodeActionKinds: [vscode.CodeActionKind.QuickFix]
+            }
+        );
     }
 
     public start() {
@@ -57,10 +80,12 @@ export class CargoWatchProvider implements vscode.Disposable {
             return;
         }
 
-        let args = 'check --all-targets --message-format json';
-        if (Server.config.cargoWatchOptions.checkArguments.length > 0) {
+        let args =
+            Server.config.cargoWatchOptions.command +
+            ' --all-targets --message-format json';
+        if (Server.config.cargoWatchOptions.command.length > 0) {
             // Excape the double quote string:
-            args += ' ' + Server.config.cargoWatchOptions.checkArguments;
+            args += ' ' + Server.config.cargoWatchOptions.arguments;
         }
         // Windows handles arguments differently than the unix-likes, so we need to wrap the args in double quotes
         if (process.platform === 'win32') {
@@ -123,6 +148,14 @@ export class CargoWatchProvider implements vscode.Disposable {
         this.diagnosticCollection.dispose();
         this.outputChannel.dispose();
         this.statusDisplay.dispose();
+        this.codeActionDispose.dispose();
+    }
+
+    public provideCodeActions(
+        document: vscode.TextDocument
+    ): vscode.ProviderResult<Array<vscode.Command | vscode.CodeAction>> {
+        const documentActions = this.codeActions[document.uri.toString()];
+        return documentActions || [];
     }
 
     private logInfo(line: string) {
@@ -143,6 +176,7 @@ export class CargoWatchProvider implements vscode.Disposable {
     private parseLine(line: string) {
         if (line.startsWith('[Running')) {
             this.diagnosticCollection.clear();
+            this.codeActions = {};
             this.statusDisplay.show();
         }
 
@@ -150,34 +184,65 @@ export class CargoWatchProvider implements vscode.Disposable {
             this.statusDisplay.hide();
         }
 
-        function getLevel(s: string): vscode.DiagnosticSeverity {
-            if (s === 'error') {
-                return vscode.DiagnosticSeverity.Error;
+        function areDiagnosticsEqual(
+            left: vscode.Diagnostic,
+            right: vscode.Diagnostic
+        ): boolean {
+            return (
+                left.source === right.source &&
+                left.severity === right.severity &&
+                left.range.isEqual(right.range) &&
+                left.message === right.message
+            );
+        }
+
+        function areCodeActionsEqual(
+            left: vscode.CodeAction,
+            right: vscode.CodeAction
+        ): boolean {
+            if (
+                left.kind !== right.kind ||
+                left.title !== right.title ||
+                !left.edit ||
+                !right.edit
+            ) {
+                return false;
             }
-            if (s.startsWith('warn')) {
-                return vscode.DiagnosticSeverity.Warning;
+
+            const leftEditEntries = left.edit.entries();
+            const rightEditEntries = right.edit.entries();
+
+            if (leftEditEntries.length !== rightEditEntries.length) {
+                return false;
             }
-            return vscode.DiagnosticSeverity.Information;
-        }
 
-        // Reference:
-        // https://github.com/rust-lang/rust/blob/master/src/libsyntax/json.rs
-        interface RustDiagnosticSpan {
-            line_start: number;
-            line_end: number;
-            column_start: number;
-            column_end: number;
-            is_primary: boolean;
-            file_name: string;
-        }
+            for (let i = 0; i < leftEditEntries.length; i++) {
+                const [leftUri, leftEdits] = leftEditEntries[i];
+                const [rightUri, rightEdits] = rightEditEntries[i];
+
+                if (leftUri.toString() !== rightUri.toString()) {
+                    return false;
+                }
+
+                if (leftEdits.length !== rightEdits.length) {
+                    return false;
+                }
+
+                for (let j = 0; j < leftEdits.length; j++) {
+                    const leftEdit = leftEdits[j];
+                    const rightEdit = rightEdits[j];
+
+                    if (!leftEdit.range.isEqual(rightEdit.range)) {
+                        return false;
+                    }
 
-        interface RustDiagnostic {
-            spans: RustDiagnosticSpan[];
-            rendered: string;
-            level: string;
-            code?: {
-                code: string;
-            };
+                    if (leftEdit.newText !== rightEdit.newText) {
+                        return false;
+                    }
+                }
+            }
+
+            return true;
         }
 
         interface CargoArtifact {
@@ -211,41 +276,58 @@ export class CargoWatchProvider implements vscode.Disposable {
         } else if (data.reason === 'compiler-message') {
             const msg = data.message as RustDiagnostic;
 
-            const spans = msg.spans.filter(o => o.is_primary);
-
-            // We only handle primary span right now.
-            if (spans.length > 0) {
-                const o = spans[0];
+            const mapResult = mapRustDiagnosticToVsCode(msg);
+            if (!mapResult) {
+                return;
+            }
 
-                const rendered = msg.rendered;
-                const level = getLevel(msg.level);
-                const range = new vscode.Range(
-                    new vscode.Position(o.line_start - 1, o.column_start - 1),
-                    new vscode.Position(o.line_end - 1, o.column_end - 1)
-                );
+            const { location, diagnostic, codeActions } = mapResult;
+            const fileUri = location.uri;
 
-                const fileName = path.join(
-                    vscode.workspace.rootPath!,
-                    o.file_name
-                );
-                const diagnostic = new vscode.Diagnostic(
-                    range,
-                    rendered,
-                    level
-                );
+            const diagnostics: vscode.Diagnostic[] = [
+                ...(this.diagnosticCollection!.get(fileUri) || [])
+            ];
 
-                diagnostic.source = 'rustc';
-                diagnostic.code = msg.code ? msg.code.code : undefined;
-                diagnostic.relatedInformation = [];
+            // If we're building multiple targets it's possible we've already seen this diagnostic
+            const isDuplicate = diagnostics.some(d =>
+                areDiagnosticsEqual(d, diagnostic)
+            );
 
-                const fileUrl = vscode.Uri.file(fileName!);
+            if (isDuplicate) {
+                return;
+            }
 
-                const diagnostics: vscode.Diagnostic[] = [
-                    ...(this.diagnosticCollection!.get(fileUrl) || [])
-                ];
-                diagnostics.push(diagnostic);
+            diagnostics.push(diagnostic);
+            this.diagnosticCollection!.set(fileUri, diagnostics);
+
+            if (codeActions.length) {
+                const fileUriString = fileUri.toString();
+                const existingActions = this.codeActions[fileUriString] || [];
+
+                for (const newAction of codeActions) {
+                    const existingAction = existingActions.find(existing =>
+                        areCodeActionsEqual(existing, newAction)
+                    );
+
+                    if (existingAction) {
+                        if (!existingAction.diagnostics) {
+                            existingAction.diagnostics = [];
+                        }
+                        // This action also applies to this diagnostic
+                        existingAction.diagnostics.push(diagnostic);
+                    } else {
+                        newAction.diagnostics = [diagnostic];
+                        existingActions.push(newAction);
+                    }
+                }
 
-                this.diagnosticCollection!.set(fileUrl, diagnostics);
+                // Have VsCode query us for the code actions
+                this.codeActions[fileUriString] = existingActions;
+                vscode.commands.executeCommand(
+                    'vscode.executeCodeActionProvider',
+                    fileUri,
+                    diagnostic.range
+                );
             }
         }
     }
diff --git a/editors/code/src/commands/watch_status.ts b/editors/code/src/commands/watch_status.ts
index a3b0178f2..6c1f9041b 100644
--- a/editors/code/src/commands/watch_status.ts
+++ b/editors/code/src/commands/watch_status.ts
@@ -7,13 +7,15 @@ export class StatusDisplay implements vscode.Disposable {
 
     private i = 0;
     private statusBarItem: vscode.StatusBarItem;
+    private command: string;
     private timer?: NodeJS.Timeout;
 
-    constructor() {
+    constructor(command: string) {
         this.statusBarItem = vscode.window.createStatusBarItem(
             vscode.StatusBarAlignment.Left,
             10
         );
+        this.command = command;
         this.statusBarItem.hide();
     }
 
@@ -24,11 +26,13 @@ export class StatusDisplay implements vscode.Disposable {
             this.timer ||
             setInterval(() => {
                 if (this.packageName) {
-                    this.statusBarItem!.text = `cargo check [${
+                    this.statusBarItem!.text = `cargo ${this.command} [${
                         this.packageName
                     }] ${this.frame()}`;
                 } else {
-                    this.statusBarItem!.text = `cargo check ${this.frame()}`;
+                    this.statusBarItem!.text = `cargo ${
+                        this.command
+                    } ${this.frame()}`;
                 }
             }, 300);
 
diff --git a/editors/code/src/config.ts b/editors/code/src/config.ts
index 3024546d2..10e98d753 100644
--- a/editors/code/src/config.ts
+++ b/editors/code/src/config.ts
@@ -1,5 +1,6 @@
 import * as vscode from 'vscode';
 
+import { strict } from 'assert';
 import { Server } from './server';
 
 const RA_LSP_DEBUG = process.env.__RA_LSP_SERVER_DEBUG;
@@ -9,7 +10,8 @@ export type CargoWatchTraceOptions = 'off' | 'error' | 'verbose';
 
 export interface CargoWatchOptions {
     enableOnStartup: CargoWatchStartupOptions;
-    checkArguments: string;
+    arguments: string;
+    command: string;
     trace: CargoWatchTraceOptions;
 }
 
@@ -23,7 +25,8 @@ export class Config {
     public cargoWatchOptions: CargoWatchOptions = {
         enableOnStartup: 'ask',
         trace: 'off',
-        checkArguments: ''
+        arguments: '',
+        command: ''
     };
 
     private prevEnhancedTyping: null | boolean = null;
@@ -104,12 +107,20 @@ export class Config {
             );
         }
 
-        if (config.has('cargo-watch.check-arguments')) {
-            this.cargoWatchOptions.checkArguments = config.get<string>(
-                'cargo-watch.check-arguments',
+        if (config.has('cargo-watch.arguments')) {
+            this.cargoWatchOptions.arguments = config.get<string>(
+                'cargo-watch.arguments',
                 ''
             );
         }
+
+        if (config.has('cargo-watch.command')) {
+            this.cargoWatchOptions.command = config.get<string>(
+                'cargo-watch.command',
+                ''
+            );
+        }
+
         if (config.has('lruCapacity')) {
             this.lruCapacity = config.get('lruCapacity') as number;
         }
diff --git a/editors/code/src/utils/rust_diagnostics.ts b/editors/code/src/utils/rust_diagnostics.ts
new file mode 100644
index 000000000..ed049c95e
--- /dev/null
+++ b/editors/code/src/utils/rust_diagnostics.ts
@@ -0,0 +1,226 @@
+import * as path from 'path';
+import * as vscode from 'vscode';
+
+// Reference:
+// https://github.com/rust-lang/rust/blob/master/src/libsyntax/json.rs
+export interface RustDiagnosticSpan {
+    line_start: number;
+    line_end: number;
+    column_start: number;
+    column_end: number;
+    is_primary: boolean;
+    file_name: string;
+    label?: string;
+    suggested_replacement?: string;
+    suggestion_applicability?:
+        | 'MachineApplicable'
+        | 'HasPlaceholders'
+        | 'MaybeIncorrect'
+        | 'Unspecified';
+}
+
+export interface RustDiagnostic {
+    spans: RustDiagnosticSpan[];
+    rendered: string;
+    message: string;
+    level: string;
+    code?: {
+        code: string;
+    };
+    children: RustDiagnostic[];
+}
+
+export interface MappedRustDiagnostic {
+    location: vscode.Location;
+    diagnostic: vscode.Diagnostic;
+    codeActions: vscode.CodeAction[];
+}
+
+interface MappedRustChildDiagnostic {
+    related?: vscode.DiagnosticRelatedInformation;
+    codeAction?: vscode.CodeAction;
+    messageLine?: string;
+}
+
+/**
+ * Converts a Rust level string to a VsCode severity
+ */
+function mapLevelToSeverity(s: string): vscode.DiagnosticSeverity {
+    if (s === 'error') {
+        return vscode.DiagnosticSeverity.Error;
+    }
+    if (s.startsWith('warn')) {
+        return vscode.DiagnosticSeverity.Warning;
+    }
+    return vscode.DiagnosticSeverity.Information;
+}
+
+/**
+ * Converts a Rust span to a VsCode location
+ */
+function mapSpanToLocation(span: RustDiagnosticSpan): vscode.Location {
+    const fileName = path.join(vscode.workspace.rootPath!, span.file_name);
+    const fileUri = vscode.Uri.file(fileName);
+
+    const range = new vscode.Range(
+        new vscode.Position(span.line_start - 1, span.column_start - 1),
+        new vscode.Position(span.line_end - 1, span.column_end - 1)
+    );
+
+    return new vscode.Location(fileUri, range);
+}
+
+/**
+ * Converts a secondary Rust span to a VsCode related information
+ *
+ * If the span is unlabelled this will return `undefined`.
+ */
+function mapSecondarySpanToRelated(
+    span: RustDiagnosticSpan
+): vscode.DiagnosticRelatedInformation | undefined {
+    if (!span.label) {
+        // Nothing to label this with
+        return;
+    }
+
+    const location = mapSpanToLocation(span);
+    return new vscode.DiagnosticRelatedInformation(location, span.label);
+}
+
+/**
+ * Determines if diagnostic is related to unused code
+ */
+function isUnusedOrUnnecessary(rd: RustDiagnostic): boolean {
+    if (!rd.code) {
+        return false;
+    }
+
+    return [
+        'dead_code',
+        'unknown_lints',
+        'unused_attributes',
+        'unused_imports',
+        'unused_macros',
+        'unused_variables'
+    ].includes(rd.code.code);
+}
+
+/**
+ * Converts a Rust child diagnostic to a VsCode related information
+ *
+ * This can have three outcomes:
+ *
+ * 1. If this is no primary span this will return a `noteLine`
+ * 2. If there is a primary span with a suggested replacement it will return a
+ *    `codeAction`.
+ * 3. If there is a primary span without a suggested replacement it will return
+ *    a `related`.
+ */
+function mapRustChildDiagnostic(rd: RustDiagnostic): MappedRustChildDiagnostic {
+    const span = rd.spans.find(s => s.is_primary);
+
+    if (!span) {
+        // `rustc` uses these spanless children as a way to print multi-line
+        // messages
+        return { messageLine: rd.message };
+    }
+
+    // If we have a primary span use its location, otherwise use the parent
+    const location = mapSpanToLocation(span);
+
+    // We need to distinguish `null` from an empty string
+    if (span && typeof span.suggested_replacement === 'string') {
+        const edit = new vscode.WorkspaceEdit();
+        edit.replace(location.uri, location.range, span.suggested_replacement);
+
+        // Include our replacement in the label unless it's empty
+        const title = span.suggested_replacement
+            ? `${rd.message}: \`${span.suggested_replacement}\``
+            : rd.message;
+
+        const codeAction = new vscode.CodeAction(
+            title,
+            vscode.CodeActionKind.QuickFix
+        );
+
+        codeAction.edit = edit;
+        codeAction.isPreferred =
+            span.suggestion_applicability === 'MachineApplicable';
+
+        return { codeAction };
+    } else {
+        const related = new vscode.DiagnosticRelatedInformation(
+            location,
+            rd.message
+        );
+
+        return { related };
+    }
+}
+
+/**
+ * Converts a Rust root diagnostic to VsCode form
+ *
+ * This flattens the Rust diagnostic by:
+ *
+ * 1. Creating a `vscode.Diagnostic` with the root message and primary span.
+ * 2. Adding any labelled secondary spans to `relatedInformation`
+ * 3. Categorising child diagnostics as either Quick Fix actions,
+ *    `relatedInformation` or additional message lines.
+ *
+ * If the diagnostic has no primary span this will return `undefined`
+ */
+export function mapRustDiagnosticToVsCode(
+    rd: RustDiagnostic
+): MappedRustDiagnostic | undefined {
+    const codeActions = [];
+
+    const primarySpan = rd.spans.find(s => s.is_primary);
+    if (!primarySpan) {
+        return;
+    }
+
+    const location = mapSpanToLocation(primarySpan);
+    const secondarySpans = rd.spans.filter(s => !s.is_primary);
+
+    const severity = mapLevelToSeverity(rd.level);
+
+    const vd = new vscode.Diagnostic(location.range, rd.message, severity);
+
+    vd.source = 'rustc';
+    vd.code = rd.code ? rd.code.code : undefined;
+    vd.relatedInformation = [];
+
+    for (const secondarySpan of secondarySpans) {
+        const related = mapSecondarySpanToRelated(secondarySpan);
+        if (related) {
+            vd.relatedInformation.push(related);
+        }
+    }
+
+    for (const child of rd.children) {
+        const { related, codeAction, messageLine } = mapRustChildDiagnostic(
+            child
+        );
+
+        if (related) {
+            vd.relatedInformation.push(related);
+        }
+        if (codeAction) {
+            codeActions.push(codeAction);
+        }
+        if (messageLine) {
+            vd.message += `\n${messageLine}`;
+        }
+    }
+
+    if (isUnusedOrUnnecessary(rd)) {
+        vd.tags = [vscode.DiagnosticTag.Unnecessary];
+    }
+
+    return {
+        location,
+        diagnostic: vd,
+        codeActions
+    };
+}