Preserve VS Code settings comments during merge

install/merge-vscode-settings.test.mjs

@@ -0,0 +1,216 @@
+import assert from 'node:assert/strict';
+import { spawnSync } from 'node:child_process';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import test from 'node:test';
+import { fileURLToPath } from 'node:url';
+
+const scriptDir = path.dirname(fileURLToPath(import.meta.url));
+const repoRoot = path.resolve(scriptDir, '..');
+const mergeScript = path.join(scriptDir, 'merge-vscode-settings.mjs');
+const templateFile = path.join(repoRoot, 'config', 'vscode', 'settings.template.jsonc');
+
+function stripJsonComments(input) {
+  let output = '';
+  let inString = false;
+  let escaping = false;
+  let inLineComment = false;
+  let inBlockComment = false;
+
+  for (let index = 0; index < input.length; index += 1) {
+    const char = input[index];
+    const next = input[index + 1];
+
+    if (inLineComment) {
+      if (char === '\n') {
+        inLineComment = false;
+        output += char;
+      }
+      continue;
+    }
+
+    if (inBlockComment) {
+      if (char === '*' && next === '/') {
+        inBlockComment = false;
+        index += 1;
+      } else if (char === '\n' || char === '\r') {
+        output += char;
+      }
+      continue;
+    }
+
+    if (inString) {
+      output += char;
+      if (escaping) {
+        escaping = false;
+      } else if (char === '\\') {
+        escaping = true;
+      } else if (char === '"') {
+        inString = false;
+      }
+      continue;
+    }
+
+    if (char === '"') {
+      inString = true;
+      output += char;
+      continue;
+    }
+
+    if (char === '/' && next === '/') {
+      inLineComment = true;
+      index += 1;
+      continue;
+    }
+
+    if (char === '/' && next === '*') {
+      inBlockComment = true;
+      index += 1;
+      continue;
+    }
+
+    output += char;
+  }
+
+  return output;
+}
+
+function stripTrailingCommas(input) {
+  let output = '';
+  let inString = false;
+  let escaping = false;
+
+  for (let index = 0; index < input.length; index += 1) {
+    const char = input[index];
+
+    if (inString) {
+      output += char;
+      if (escaping) {
+        escaping = false;
+      } else if (char === '\\') {
+        escaping = true;
+      } else if (char === '"') {
+        inString = false;
+      }
+      continue;
+    }
+
+    if (char === '"') {
+      inString = true;
+      output += char;
+      continue;
+    }
+
+    if (char === ',') {
+      let lookahead = index + 1;
+      while (lookahead < input.length && /\s/.test(input[lookahead])) {
+        lookahead += 1;
+      }
+      if (input[lookahead] === '}' || input[lookahead] === ']') {
+        continue;
+      }
+    }
+
+    output += char;
+  }
+
+  return output;
+}
+
+function parseJsonc(input) {
+  return JSON.parse(stripTrailingCommas(stripJsonComments(input)));
+}
+
+function runMerge(targetFile) {
+  return spawnSync(
+    process.execPath,
+    [
+      mergeScript,
+      '--target',
+      targetFile,
+      '--template',
+      templateFile,
+      '--set',
+      'COPILOT_RESOURCES_HOME=/repo/home',
+    ],
+    {
+      cwd: repoRoot,
+      encoding: 'utf8',
+    }
+  );
+}
+
+test('preserves comments and custom nested entries while inserting managed settings', () => {
+  const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'copilot-settings-'));
+  const targetFile = path.join(tempDir, 'settings.json');
+
+  fs.writeFileSync(
+    targetFile,
+    `{
+  // keep this comment
+  "workbench.colorTheme": "GitHub Dark Mode",
+
+  // preserve nested comments
+  "chat.agentFilesLocations": {
+    // custom agents stay
+    "/custom/agents": true
+  },
+
+  "chat.instructionsFilesLocations": {
+    "/old/instructions": true,
+    "~/.claude/rules": false,
+  }
+}
+`,
+    'utf8'
+  );
+
+  const result = runMerge(targetFile);
+  assert.equal(result.status, 0, result.stderr);
+
+  const output = fs.readFileSync(targetFile, 'utf8');
+  assert.match(output, /\/\/ keep this comment/);
+  assert.match(output, /\/\/ preserve nested comments/);
+  assert.match(output, /\/\/ custom agents stay/);
+  assert.match(output, /"\/custom\/agents": true/);
+  assert.match(output, /"\/repo\/home\/resources\/agents": true/);
+
+  const parsed = parseJsonc(output);
+  assert.equal(parsed['workbench.colorTheme'], 'GitHub Dark Mode');
+  assert.equal(parsed['chat.agentFilesLocations']['/custom/agents'], true);
+  assert.equal(parsed['chat.agentFilesLocations']['/repo/home/resources/agents'], true);
+  assert.equal(parsed['chat.agentFilesLocations']['~/.copilot/agents'], true);
+  assert.equal(parsed['chat.instructionsFilesLocations']['/old/instructions'], true);
+  assert.equal(parsed['chat.instructionsFilesLocations']['/repo/home/resources/instructions'], true);
+  assert.equal(parsed['chat.instructionsFilesLocations']['~/.claude/rules'], true);
+});
+
+test('second run is idempotent and keeps the file text unchanged', () => {
+  const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'copilot-settings-'));
+  const targetFile = path.join(tempDir, 'settings.json');
+
+  fs.writeFileSync(
+    targetFile,
+    `{
+  // user comment
+  "chat.promptFilesLocations": {
+    "/custom/prompts": true
+  }
+}
+`,
+    'utf8'
+  );
+
+  const firstRun = runMerge(targetFile);
+  assert.equal(firstRun.status, 0, firstRun.stderr);
+  const firstOutput = fs.readFileSync(targetFile, 'utf8');
+
+  const secondRun = runMerge(targetFile);
+  assert.equal(secondRun.status, 0, secondRun.stderr);
+  assert.match(secondRun.stdout, /already up to date/);
+
+  const secondOutput = fs.readFileSync(targetFile, 'utf8');
+  assert.equal(secondOutput, firstOutput);
+  assert.match(secondOutput, /\/\/ user comment/);
+});