Merge #5885

5885: Make inlay hints colors more configurable r=matklad a=Veetaha

**[BREAKING CHANGE]**

Tackles https://github.com/rust-analyzer/rust-analyzer/issues/5337#issuecomment-680018601 and generally related to #5337.

Added `foreground/background` color configurations with optional more specific overrides `foreground.(type|parameter|chaining)Hints`.

One problem I see is that the config keys are long and don't fit into the on-hover hints in the `settings.json` file entirely...

<details>
<summary>Demo</summary>

![demo](https://user-images.githubusercontent.com/36276403/91238334-77fc3b00-e745-11ea-836b-2822015ece98.gif)

</details>

Co-authored-by: Veetaha <[email protected]>

3 files changed, 117 insertions, 49 deletions

diff --git a/docs/user/manual.adoc b/docs/user/manual.adoc
index 8c966288b..b15c9ee7f 100644
--- a/docs/user/manual.adoc
+++ b/docs/user/manual.adoc
@@ -367,6 +367,30 @@ include::./generated_assists.adoc[]
 
 == Editor Features
 === VS Code
+
+==== Color configurations
+
+It is possible to change the foreground/background color of inlay hints. Just add this to your
+`settings.json`:
+
+[source,jsonc]
+----
+{
+  "workbench.colorCustomizations": {
+    // Name of the theme you are currently using
+    "[Default Dark+]": {
+      "rust_analyzer.inlayHints.foreground": "#868686f0",
+      "rust_analyzer.inlayHints.background": "#3d3d3d48",
+
+      // Overrides for specific kinds of inlay hints
+      "rust_analyzer.inlayHints.foreground.typeHints": "#fdb6fdf0",
+      "rust_analyzer.inlayHints.foreground.paramHints": "#fdb6fdf0",
+      "rust_analyzer.inlayHints.background.chainingHints": "#6b0c0c81"
+    }
+  }
+}
+----
+
 ==== Special `when` clause context for keybindings.
 You may use `inRustProject` context to configure keybindings for rust projects only. For example:
 [source,json]
diff --git a/editors/code/package.json b/editors/code/package.json
index f079f73b8..93d94ed12 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -712,8 +712,8 @@
         ],
         "colors": [
             {
-                "id": "rust_analyzer.inlayHint",
-                "description": "Color for inlay hints",
+                "id": "rust_analyzer.inlayHints.foreground",
+                "description": "Foreground color of inlay hints (is overriden by more specific rust_analyzer.inlayHints.foreground.* configurations)",
                 "defaults": {
                     "dark": "#A0A0A0F0",
                     "light": "#747474",
@@ -721,6 +721,69 @@
                 }
             },
             {
+                "id": "rust_analyzer.inlayHints.background",
+                "description": "Background color of inlay hints (is overriden by more specific rust_analyzer.inlayHints.background.* configurations)",
+                "defaults": {
+                    "dark": "#11223300",
+                    "light": "#11223300",
+                    "highContrast": "#11223300"
+                }
+            },
+            {
+                "id": "rust_analyzer.inlayHints.foreground.typeHints",
+                "description": "Foreground color of inlay type hints for variables (overrides rust_analyzer.inlayHints.foreground)",
+                "defaults": {
+                    "dark": "rust_analyzer.inlayHints.foreground",
+                    "light": "rust_analyzer.inlayHints.foreground",
+                    "highContrast": "rust_analyzer.inlayHints.foreground"
+                }
+            },
+            {
+                "id": "rust_analyzer.inlayHints.foreground.chainingHints",
+                "description": "Foreground color of inlay type hints for method chains (overrides rust_analyzer.inlayHints.foreground)",
+                "defaults": {
+                    "dark": "rust_analyzer.inlayHints.foreground",
+                    "light": "rust_analyzer.inlayHints.foreground",
+                    "highContrast": "rust_analyzer.inlayHints.foreground"
+                }
+            },
+            {
+                "id": "rust_analyzer.inlayHints.foreground.parameterHints",
+                "description": "Foreground color of function parameter name inlay hints at the call site (overrides rust_analyzer.inlayHints.foreground)",
+                "defaults": {
+                    "dark": "rust_analyzer.inlayHints.foreground",
+                    "light": "rust_analyzer.inlayHints.foreground",
+                    "highContrast": "rust_analyzer.inlayHints.foreground"
+                }
+            },
+            {
+                "id": "rust_analyzer.inlayHints.background.typeHints",
+                "description": "Background color of inlay type hints for variables (overrides rust_analyzer.inlayHints.background)",
+                "defaults": {
+                    "dark": "rust_analyzer.inlayHints.background",
+                    "light": "rust_analyzer.inlayHints.background",
+                    "highContrast": "rust_analyzer.inlayHints.background"
+                }
+            },
+            {
+                "id": "rust_analyzer.inlayHints.background.chainingHints",
+                "description": "Background color of inlay type hints for method chains (overrides rust_analyzer.inlayHints.background)",
+                "defaults": {
+                    "dark": "rust_analyzer.inlayHints.background",
+                    "light": "rust_analyzer.inlayHints.background",
+                    "highContrast": "rust_analyzer.inlayHints.background"
+                }
+            },
+            {
+                "id": "rust_analyzer.inlayHints.background.parameterHints",
+                "description": "Background color of function parameter name inlay hints at the call site (overrides rust_analyzer.inlayHints.background)",
+                "defaults": {
+                    "dark": "rust_analyzer.inlayHints.background",
+                    "light": "rust_analyzer.inlayHints.background",
+                    "highContrast": "rust_analyzer.inlayHints.background"
+                }
+            },
+            {
                 "id": "rust_analyzer.syntaxTreeBorder",
                 "description": "Color of the border displayed in the Rust source code for the selected syntax node (see \"Show Syntax Tree\" command)",
                 "defaults": {
diff --git a/editors/code/src/inlay_hints.ts b/editors/code/src/inlay_hints.ts
index 9e6d6045f..7b481fc72 100644
--- a/editors/code/src/inlay_hints.ts
+++ b/editors/code/src/inlay_hints.ts
@@ -39,54 +39,35 @@ export function activateInlayHints(ctx: Ctx) {
     maybeUpdater.onConfigChange();
 }
 
-
-const typeHints = {
-    decorationType: vscode.window.createTextEditorDecorationType({
-        after: {
-            color: new vscode.ThemeColor('rust_analyzer.inlayHint'),
-            fontStyle: "normal",
-        }
-    }),
-
-    toDecoration(hint: ra.InlayHint.TypeHint, conv: lc.Protocol2CodeConverter): vscode.DecorationOptions {
-        return {
-            range: conv.asRange(hint.range),
-            renderOptions: { after: { contentText: `: ${hint.label}` } }
-        };
-    }
-};
-
-const paramHints = {
-    decorationType: vscode.window.createTextEditorDecorationType({
-        before: {
-            color: new vscode.ThemeColor('rust_analyzer.inlayHint'),
-            fontStyle: "normal",
-        }
-    }),
-
-    toDecoration(hint: ra.InlayHint.ParamHint, conv: lc.Protocol2CodeConverter): vscode.DecorationOptions {
-        return {
-            range: conv.asRange(hint.range),
-            renderOptions: { before: { contentText: `${hint.label}: ` } }
-        };
-    }
-};
-
-const chainingHints = {
-    decorationType: vscode.window.createTextEditorDecorationType({
-        after: {
-            color: new vscode.ThemeColor('rust_analyzer.inlayHint'),
-            fontStyle: "normal",
+const typeHints = createHintStyle("type");
+const paramHints = createHintStyle("parameter");
+const chainingHints = createHintStyle("chaining");
+
+function createHintStyle(hintKind: "type" | "parameter" | "chaining") {
+    const [pos, render] = ({
+        type: ["after", (label: string) => `: ${label}`],
+        parameter: ["before", (label: string) => `${label}: `],
+        chaining: ["after", (label: string) => `: ${label}`],
+    } as const)[hintKind];
+
+    const fg = new vscode.ThemeColor(`rust_analyzer.inlayHints.foreground.${hintKind}Hints`);
+    const bg = new vscode.ThemeColor(`rust_analyzer.inlayHints.background.${hintKind}Hints`);
+    return {
+        decorationType: vscode.window.createTextEditorDecorationType({
+            [pos]: {
+                color: fg,
+                backgroundColor: bg,
+                fontStyle: "normal",
+            },
+        }),
+        toDecoration(hint: ra.InlayHint, conv: lc.Protocol2CodeConverter): vscode.DecorationOptions {
+            return {
+                range: conv.asRange(hint.range),
+                renderOptions: { [pos]: { contentText: render(hint.label) } }
+            };
         }
-    }),
-
-    toDecoration(hint: ra.InlayHint.ChainingHint, conv: lc.Protocol2CodeConverter): vscode.DecorationOptions {
-        return {
-            range: conv.asRange(hint.range),
-            renderOptions: { after: { contentText: ` ${hint.label}` } }
-        };
-    }
-};
+    };
+}
 
 class HintsUpdater implements Disposable {
     private sourceFiles = new Map<string, RustSourceFile>(); // map Uri -> RustSourceFile