Use C++ formatting for C++ splits in testdata files. (#7385)

Refactor the textmate grammar to use a different scope for testdata
files. Move the existing handling for `CHECK:STDOUT:` there, and add
handling for C++ file splits there too.

Assisted-by: Gemini via Antigravity

utils/vscode/BUILD

@@ -8,8 +8,8 @@ exports_files(
     [
         "package.json",
         "carbon.tmLanguage.json",
+        "carbon-testdata.tmLanguage.json",
         "semir.tmLanguage.json",
-        "carbon-check-test.tmLanguage.json",
         "language-configuration.json",
         "images/icon.png",
     ],

utils/vscode/carbon-check-test.tmLanguage.json

@@ -1,21 +0,0 @@
-{
-  "$schema": "https://raw.githubusercontent.com/martinring/tmlanguage/master/tmlanguage.json",
-  "scopeName": "source.carbon-check-test",
-  "injectionSelector": "L:source.carbon",
-  "patterns": [
-    {
-      "begin": "^(\\s*//\\s*CHECK:STDOUT:)",
-      "beginCaptures": {
-        "1": {
-          "name": "comment.line.carbon"
-        }
-      },
-      "end": "$",
-      "patterns": [
-        {
-          "include": "source.carbon-semir"
-        }
-      ]
-    }
-  ]
-}

utils/vscode/carbon-testdata.tmLanguage.json

@@ -0,0 +1,56 @@
+{
+  "$schema": "https://raw.githubusercontent.com/martinring/tmlanguage/master/tmlanguage.json",
+  "name": "carbon-testdata",
+  "scopeName": "source.carbon-testdata",
+  "fileTypes": [],
+  "patterns": [
+    {
+      "include": "#cpp-file-splits"
+    },
+    {
+      "include": "#check-stdout"
+    },
+    {
+      "include": "source.carbon"
+    }
+  ],
+  "repository": {
+    "cpp-file-splits": {
+      "patterns": [
+        {
+          "comment": "C++ file split in test files",
+          "begin": "^//\\s*---\\s*([^\\s]+\\.(h|hh|hpp|hxx|h\\+\\+|cpp|cc|cxx|c\\+\\+|c|H|HH|HPP|HXX|H\\+\\+|CPP|CC|CXX|C\\+\\+|C))\\s*$",
+          "beginCaptures": {
+            "0": { "name": "comment.line.carbon" }
+          },
+          "end": "^(?=//\\s*---)",
+          "contentName": "meta.embedded.block.cpp",
+          "patterns": [
+            {
+              "include": "source.cpp"
+            }
+          ]
+        }
+      ]
+    },
+    "check-stdout": {
+      "patterns": [
+        {
+          "comment": "Highlight compile output / SemIR in CHECK:STDOUT lines",
+          "begin": "^(\\s*//\\s*CHECK:STDOUT:)",
+          "beginCaptures": {
+            "1": {
+              "name": "comment.line.carbon"
+            }
+          },
+          "end": "$",
+          "patterns": [
+            {
+              "include": "source.carbon-semir"
+            }
+          ]
+        }
+      ]
+    }
+  }
+}

utils/vscode/package.json

@@ -18,6 +18,16 @@
   "main": "./dist/extension.js",
   "contributes": {
     "languages": [
+      {
+        "id": "carbon-testdata",
+        "aliases": [
+          "Carbon Testdata"
+        ],
+        "filenamePatterns": [
+          "**/testdata/**/*.carbon"
+        ],
+        "configuration": "./language-configuration.json"
+      },
       {
         "id": "carbon",
         "aliases": [
@@ -39,6 +49,11 @@
       }
     ],
     "grammars": [
+      {
+        "language": "carbon-testdata",
+        "scopeName": "source.carbon-testdata",
+        "path": "./carbon-testdata.tmLanguage.json"
+      },
       {
         "language": "carbon",
         "scopeName": "source.carbon",
@@ -48,13 +63,6 @@
         "language": "semir",
         "scopeName": "source.carbon-semir",
         "path": "./semir.tmLanguage.json"
-      },
-      {
-        "scopeName": "source.carbon-check-test",
-        "path": "./carbon-check-test.tmLanguage.json",
-        "injectTo": [
-          "source.carbon"
-        ]
       }
     ],
     "configuration": {

utils/vscode/src/extension.ts

@@ -36,7 +36,7 @@ function updateSplitLineNumbers(editor: TextEditor | undefined) {
     return;
   }
   const document = editor.document;
-  if (!document.fileName.includes('/testdata/')) {
+  if (document.languageId !== 'carbon-testdata') {
     return;
   }
 
@@ -189,7 +189,10 @@ export function activate(context: ExtensionContext) {
   };
 
   const clientOptions: LanguageClientOptions = {
-    documentSelector: [{ language: 'carbon' }],
+    documentSelector: [
+      { language: 'carbon' },
+      { language: 'carbon-testdata' },
+    ],
   };
 
   // Create and start the client.