5 files changed, 29 insertions, 6 deletions

diff --git a/crates/ra_syntax/src/syntax_text.rs b/crates/ra_syntax/src/syntax_text.rs
index bff1ed5a0..c9038cd5c 100644
--- a/crates/ra_syntax/src/syntax_text.rs
+++ b/crates/ra_syntax/src/syntax_text.rs
@@ -35,7 +35,8 @@ impl<'a> SyntaxText<'a> {
     }
 
     pub fn to_smol_string(&self) -> SmolStr {
-        // TODO: `impl iter::FromIterator<&str> for SmolStr`
+        // FIXME: use `self.chunks().collect()` here too once
+        // https://github.com/matklad/smol_str/pull/12 is merged and published
         self.to_string().into()
     }
 
diff --git a/docs/user/features.md b/docs/user/features.md
index 22470bc56..b6e6008c4 100644
--- a/docs/user/features.md
+++ b/docs/user/features.md
@@ -470,3 +470,12 @@ There also snippet completions:
 
 - `tfn` -> `#[test] fn f(){}`
 
+### Code highlighting
+
+Experimental feature to let rust-analyzer highlight Rust code instead of using the
+default highlighter.
+
+#### Rainbow highlighting
+
+Experimental feature that, given code highlighting using rust-analyzer is
+active, will pick unique colors for identifiers.
diff --git a/editors/code/package.json b/editors/code/package.json
index d8ba914f5..05c808394 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -164,6 +164,11 @@
                     "default": false,
                     "description": "Highlight Rust code (overrides built-in syntax highlighting)"
                 },
+                "rust-analyzer.rainbowHighlightingOn": {
+                    "type": "boolean",
+                    "default": false,
+                    "description": "When highlighting Rust code, use a unique color per identifier"
+                },
                 "rust-analyzer.showWorkspaceLoadedNotification": {
                     "type": "boolean",
                     "default": true,
diff --git a/editors/code/src/config.ts b/editors/code/src/config.ts
index 481a5e5f1..8d73a6b34 100644
--- a/editors/code/src/config.ts
+++ b/editors/code/src/config.ts
@@ -15,6 +15,7 @@ export interface CargoWatchOptions {
 
 export class Config {
     public highlightingOn = true;
+    public rainbowHighlightingOn = false;
     public enableEnhancedTyping = true;
     public raLspServerPath = RA_LSP_DEBUG || 'ra_lsp_server';
     public showWorkspaceLoadedNotification = true;
@@ -39,6 +40,12 @@ export class Config {
             this.highlightingOn = config.get('highlightingOn') as boolean;
         }
 
+        if (config.has('rainbowHighlightingOn')) {
+            this.rainbowHighlightingOn = config.get(
+                'rainbowHighlightingOn'
+            ) as boolean;
+        }
+
         if (config.has('showWorkspaceLoadedNotification')) {
             this.showWorkspaceLoadedNotification = config.get(
                 'showWorkspaceLoadedNotification'
diff --git a/editors/code/src/highlighting.ts b/editors/code/src/highlighting.ts
index 4597db08f..52a0bd4bb 100644
--- a/editors/code/src/highlighting.ts
+++ b/editors/code/src/highlighting.ts
@@ -7,7 +7,7 @@ import { Server } from './server';
 export interface Decoration {
     range: lc.Range;
     tag: string;
-    id?: string;
+    bindingHash?: string;
 }
 
 // Based on this HSL-based color generator: https://gist.github.com/bendc/76c48ce53299e6078a76
@@ -92,6 +92,7 @@ export class Highlighter {
 
         const byTag: Map<string, vscode.Range[]> = new Map();
         const colorfulIdents: Map<string, vscode.Range[]> = new Map();
+        const rainbowTime = Server.config.rainbowHighlightingOn;
 
         for (const tag of this.decorations.keys()) {
             byTag.set(tag, []);
@@ -102,12 +103,12 @@ export class Highlighter {
                 continue;
             }
 
-            if (d.id) {
-                if (!colorfulIdents.has(d.id)) {
-                    colorfulIdents.set(d.id, []);
+            if (rainbowTime && d.bindingHash) {
+                if (!colorfulIdents.has(d.bindingHash)) {
+                    colorfulIdents.set(d.bindingHash, []);
                 }
                 colorfulIdents
-                    .get(d.id)!
+                    .get(d.bindingHash)!
                     .push(
                         Server.client.protocol2CodeConverter.asRange(d.range)
                     );