fix(typescript): robust outDir containment; gate temp outDir cleanup in watch mode\n\n- Guard containment with cross-drive root check and absolute-relative detection\n- Skip over-exclusion when filterRoot is false by falling back to process.cwd()\n- Delete temp outDir only for non-watch builds; clean up in closeWatcher for watch\n- Docs: clarify effective outDir exclusion and watch-mode cleanup timing\n\nRefs #1920

Author: CharlieHelps

packages/typescript/README.md

@@ -79,7 +79,7 @@ Default: `null`
 
 A [picomatch pattern](https://github.com/micromatch/picomatch), or array of patterns, which specifies the files in the build the plugin should operate on. By default all `.ts` and `.tsx` files are targeted. If your `tsconfig.json` (or plugin `compilerOptions`) sets `allowJs: true`, the default include expands to also cover `.js`, `.jsx`, `.mjs`, and `.cjs` files so that JavaScript sources are downleveled by TypeScript as well.
 
-> Note: When `allowJs` is enabled and no `outDir` is configured, this plugin creates a temporary output directory for TypeScript emit to avoid TS5055 (overwriting input files). The directory is excluded from processing and removed after the build.
+> Note: When `allowJs` is enabled and no `outDir` is configured, this plugin creates a temporary output directory for TypeScript emit to avoid TS5055 (overwriting input files). The effective `outDir` (whether user-provided or the temporary one) is excluded from plugin processing to prevent re-processing emitted files. The temporary directory is removed after a non-watch build completes; in watch mode it is removed when the watcher stops.
 
 ### `filterRoot`
 

packages/typescript/src/index.ts

@@ -69,18 +69,23 @@ export default function typescript(options: RollupTypescriptOptions = {}): Plugi
   const effectiveOutDir = parsedOptions.options.outDir
     ? path.resolve(parsedOptions.options.outDir)
     : null;
-  const filterBase = (filterRoot ?? parsedOptions.options.rootDir) || null;
-  const filterBaseAbs = filterBase ? path.resolve(filterBase) : null;
+  // Determine the base used for containment checks. If pattern resolution is disabled
+  // (filterRoot === false), fall back to process.cwd() so we don't accidentally
+  // exclude sources when e.g. outDir='.'.
+  const willResolvePatterns = filterRoot !== false;
+  const configuredBase = willResolvePatterns ? filterRoot ?? parsedOptions.options.rootDir : null;
+  const filterBaseAbs = configuredBase ? path.resolve(configuredBase) : null;
   if (effectiveOutDir) {
-    // Avoid excluding sources: skip when the filter base (rootDir) lives inside outDir
-    // Use path.relative for a robust cross-platform containment check.
-    const outDirContainsFilterBase = filterBaseAbs
-      ? (() => {
-          const rel = path.relative(effectiveOutDir, filterBaseAbs);
-          // rel === '' -> same dir; rel starts with '..' -> outside
-          return rel === '' || !(rel === '..' || rel.startsWith(`..${path.sep}`));
-        })()
-      : false;
+    // Avoid excluding sources: skip when the filter base (or cwd fallback) lives inside outDir.
+    // Use path.relative with root equality guard for cross-platform correctness.
+    const baseForContainment = filterBaseAbs ?? process.cwd();
+    const outDirContainsFilterBase = (() => {
+      // Different roots (e.g., drive letters on Windows) cannot be in a parent/child relationship
+      if (path.parse(effectiveOutDir).root !== path.parse(baseForContainment).root) return false;
+      const rel = path.relative(effectiveOutDir, baseForContainment);
+      // rel === '' -> same dir; absolute or '..' => outside
+      return rel === '' || (!rel.startsWith('..') && !path.isAbsolute(rel));
+    })();
     if (!outDirContainsFilterBase) {
       filterExclude.push(normalizePath(path.join(effectiveOutDir, '**')));
     }
@@ -146,7 +151,19 @@ export default function typescript(options: RollupTypescriptOptions = {}): Plugi
         // ESLint doesn't understand optional chaining
         // eslint-disable-next-line
         program?.close();
+        if (autoOutDir) {
+          try {
+            fs.rmSync(autoOutDir, { recursive: true, force: true });
+          } catch {
+            // ignore cleanup failures
+          }
+          autoOutDir = null;
+        }
       }
+    },
+
+    // Ensure temp outDir is removed exactly once when watch stops
+    closeWatcher() {
       if (autoOutDir) {
         try {
           fs.rmSync(autoOutDir, { recursive: true, force: true });