Add a lint-chmod task to catch stray executable bits

gulpfile.mjs

@@ -2311,6 +2311,88 @@ gulp.task("lint-licenses", function (done) {
     });
 });
 
+gulp.task("lint-chmod", function (done) {
+  console.log("\n### Checking executable bit on tracked files");
+
+  // Tracked files allowed to keep the executable bit (shebang scripts).
+  const EXECUTABLE_FILES = new Set(["test/chromium/test-telemetry.js"]);
+
+  let lsFiles;
+  try {
+    lsFiles = execSync("git ls-files -s", { encoding: "utf8" });
+  } catch (e) {
+    done(e);
+    return;
+  }
+
+  const offenders = [];
+  for (const line of lsFiles.split("\n")) {
+    if (!line) {
+      continue;
+    }
+    // "<mode> <sha> <stage>\t<path>"
+    const tab = line.indexOf("\t");
+    const mode = line.slice(0, 6);
+    const file = line.slice(tab + 1);
+    if (mode === "100755" && !EXECUTABLE_FILES.has(file)) {
+      offenders.push(file);
+    }
+  }
+
+  if (offenders.length === 0) {
+    console.log("files checked, no errors found");
+    done();
+    return;
+  }
+
+  // --fix here also stages the chmod (via `git update-index`), which is
+  // unlike every other --fix in `gulp lint` (those only touch the working
+  // tree). Restrict the auto-fix to a direct `gulp lint-chmod --fix`
+  // invocation so the umbrella `gulp lint --fix` never silently stages.
+  const fix =
+    process.argv.includes("lint-chmod") && process.argv.includes("--fix");
+  if (!fix) {
+    for (const file of offenders.sort()) {
+      console.log(`  Unexpected executable bit: ${file}`);
+    }
+    done(
+      new Error(
+        "Executable-bit check failed (run `gulp lint-chmod --fix` to clear, then commit)."
+      )
+    );
+    return;
+  }
+
+  // Drop the bit on disk too: `git update-index --chmod=-x` only edits the
+  // index, so a later `git add` would re-read the still-executable working
+  // tree and undo the staged chmod.
+  for (const file of offenders) {
+    try {
+      const { mode } = fs.statSync(file);
+      fs.chmodSync(file, mode & ~0o111);
+    } catch (e) {
+      done(e);
+      return;
+    }
+  }
+
+  // Chunk the path list so we stay well under ARG_MAX.
+  const CHUNK = 256;
+  for (let i = 0; i < offenders.length; i += CHUNK) {
+    const result = spawnSync(
+      "git",
+      ["update-index", "--chmod=-x", "--", ...offenders.slice(i, i + CHUNK)],
+      { stdio: "inherit" }
+    );
+    if (result.status !== 0) {
+      done(new Error("git update-index failed."));
+      return;
+    }
+  }
+  console.log(`cleared executable bit on ${offenders.length} file(s)`);
+  done();
+});
+
 gulp.task("lint", function (done) {
   console.log("\n### Linting JS/CSS/JSON/SVG/HTML files");
 
@@ -2375,7 +2457,7 @@ gulp.task("lint", function (done) {
       return;
     }
 
-    gulp.task("lint-licenses")(done);
+    gulp.series("lint-licenses", "lint-chmod")(done);
   });
 });