fix(compiler): use TypeScript sys hooks instead of fs monkeypatching to detect writes/deletes in previous output directories

changelog.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 2026-03-05 - 4.2.1 - fix(compiler)
+use TypeScript sys hooks instead of fs monkeypatching to detect writes/deletes in previous output directories
+
+- Replace direct fs.* monkeypatching with interception of typescript.sys.writeFile, typescript.sys.deleteFile and typescript.sys.createDirectory
+- Add guards for optional sys.deleteFile before overriding it and preserve original sys methods to restore after compilation
+- Update diagnostic messages to reference TypeScript sys ops and add an informational message when no ops are observed
+- Reduce surface area of changes by avoiding global fs changes and focusing on TypeScript's sys API for safer interception
+
 ## 2026-03-05 - 4.2.0 - feat(mod_compiler)
 add diagnostic interception of fs operations to detect and report unexpected file system changes in previously compiled output directories during compilation
 

ts/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@git.zone/tsbuild',
-  version: '4.2.0',
+  version: '4.2.1',
   description: 'A tool for compiling TypeScript files using the latest nightly features, offering flexible APIs and a CLI for streamlined development.'
 }

ts/mod_compiler/classes.tscompiler.ts

@@ -380,45 +380,33 @@ export class TsCompiler {
         fileCount: absoluteFiles.length,
       };
 
-      // Diagnostic: intercept fs operations during compilation to detect
+      // Diagnostic: intercept TypeScript sys operations during compilation to detect
-      // any unexpected deletions in previously compiled output directories
+      // any unexpected writes/deletes in previously compiled output directories
       const watchedDirs = successfulOutputDirs.filter(d => d !== destDir);
-      const origUnlink = fs.unlinkSync;
-      const origRm = fs.rmSync;
-      const origRmdir = fs.rmdirSync;
-      const origRename = fs.renameSync;
-      const origWriteFile = fs.writeFileSync;
       let interceptedOps: string[] = [];
+      const origSysWriteFile = typescript.sys.writeFile;
+      const origSysDeleteFile = typescript.sys.deleteFile;
+      const origSysCreateDir = typescript.sys.createDirectory;
       if (watchedDirs.length > 0 && !isQuiet && !isJson) {
-        (fs as any).unlinkSync = (p: string, ...args: any[]) => {
+        typescript.sys.writeFile = (p: string, data: string, writeBom?: boolean) => {
-          if (watchedDirs.some(d => String(p).startsWith(d + '/'))) {
+          if (watchedDirs.some(d => p.startsWith(d + '/'))) {
-            interceptedOps.push(`unlink: ${p}`);
+            interceptedOps.push(`sys.writeFile: ${p}`);
           }
-          return origUnlink.call(fs, p, ...args);
+          return origSysWriteFile.call(typescript.sys, p, data, writeBom);
         };
-        (fs as any).rmSync = (p: string, ...args: any[]) => {
+        if (origSysDeleteFile) {
-          if (watchedDirs.some(d => String(p).startsWith(d + '/'))) {
+          typescript.sys.deleteFile = (p: string) => {
-            interceptedOps.push(`rm: ${p}`);
+            if (watchedDirs.some(d => p.startsWith(d + '/'))) {
+              interceptedOps.push(`sys.deleteFile: ${p}`);
             }
-          return origRm.call(fs, p, ...args);
+            return origSysDeleteFile!.call(typescript.sys, p);
           };
-        (fs as any).rmdirSync = (p: string, ...args: any[]) => {
-          if (watchedDirs.some(d => String(p).startsWith(d + '/'))) {
-            interceptedOps.push(`rmdir: ${p}`);
         }
-          return origRmdir.call(fs, p, ...args);
+        typescript.sys.createDirectory = (p: string) => {
-        };
+          if (watchedDirs.some(d => p.startsWith(d + '/'))) {
-        (fs as any).renameSync = (src: string, dest: string, ...args: any[]) => {
+            interceptedOps.push(`sys.createDirectory: ${p}`);
-          if (watchedDirs.some(d => String(src).startsWith(d + '/') || String(dest).startsWith(d + '/'))) {
-            interceptedOps.push(`rename: ${src} → ${dest}`);
           }
-          return origRename.call(fs, src, dest, ...args);
+          return origSysCreateDir.call(typescript.sys, p);
-        };
-        (fs as any).writeFileSync = (p: string, ...args: any[]) => {
-          if (watchedDirs.some(d => String(p).startsWith(d + '/'))) {
-            interceptedOps.push(`write: ${p}`);
-          }
-          return origWriteFile.call(fs, p, ...args);
         };
       }
 
@@ -426,21 +414,21 @@ export class TsCompiler {
       emittedFiles.push(...result.emittedFiles);
       errorSummaries.push(result.errorSummary);
 
-      // Restore original fs methods and report any intercepted operations
+      // Restore original sys methods and report any intercepted operations
       if (watchedDirs.length > 0 && !isQuiet && !isJson) {
-        (fs as any).unlinkSync = origUnlink;
+        typescript.sys.writeFile = origSysWriteFile;
-        (fs as any).rmSync = origRm;
+        typescript.sys.deleteFile = origSysDeleteFile;
-        (fs as any).rmdirSync = origRmdir;
+        typescript.sys.createDirectory = origSysCreateDir;
-        (fs as any).renameSync = origRename;
-        (fs as any).writeFileSync = origWriteFile;
         if (interceptedOps.length > 0) {
-          console.log(`   ⚠️ [diag] ${interceptedOps.length} ops on previous output dirs during compilation:`);
+          console.log(`   ⚠️ [diag] ${interceptedOps.length} TypeScript sys ops on previous output dirs:`);
           for (const op of interceptedOps.slice(0, 30)) {
             console.log(`      ${op.replace(this.cwd + '/', '')}`);
           }
           if (interceptedOps.length > 30) {
             console.log(`      ... and ${interceptedOps.length - 30} more`);
           }
+        } else {
+          console.log(`   ℹ️ [diag] No TypeScript sys ops on previous output dirs during this compilation`);
         }
       }
       diagSnap('post-compile');