JavaScript: Don't extract obviously generated files

javascript/extractor/src/com/semmle/js/dependencies/tsconfig/CompilerOptions.java

@@ -0,0 +1,13 @@
+package com.semmle.js.dependencies.tsconfig;
+
+public class CompilerOptions {
+    private String outDir;
+
+    public String getOutDir() {
+        return outDir;
+    }
+
+    public void setOutDir(String outDir) {
+        this.outDir = outDir;
+    }
+}

javascript/extractor/src/com/semmle/js/dependencies/tsconfig/TsConfigJson.java

@@ -0,0 +1,13 @@
+package com.semmle.js.dependencies.tsconfig;
+
+public class TsConfigJson {
+  private CompilerOptions compilerOptions;
+
+  public CompilerOptions getCompilerOptions() {
+    return compilerOptions;
+  }
+
+  public void setCompilerOptions(CompilerOptions compilerOptions) {
+    this.compilerOptions = compilerOptions;
+  }
+}

javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java

@@ -39,6 +39,8 @@
 
 import com.google.gson.Gson;
 import com.google.gson.JsonParseException;
+import com.semmle.js.dependencies.tsconfig.TsConfigJson;
+import com.semmle.js.dependencies.tsconfig.CompilerOptions;
 import com.semmle.js.dependencies.AsyncFetcher;
 import com.semmle.js.dependencies.DependencyResolver;
 import com.semmle.js.dependencies.packument.PackageJson;
@@ -745,6 +747,26 @@ private CompletableFuture<?> extractSource() throws IOException {
         .filter(p -> !isFileTooLarge(p))
         .sorted(PATH_ORDERING)
         .collect(Collectors.toCollection(() -> new LinkedHashSet<>()));
+    // exclude files in output directories as configured in tsconfig.json
+    final List<Path> outDirs = new ArrayList<>();
+    for (Path cfg : tsconfigFiles) {
+      try {
+        String txt = new WholeIO().read(cfg);
+        TsConfigJson root = new Gson().fromJson(txt, TsConfigJson.class);
+        if (root != null && root.getCompilerOptions() != null) {
+          if (root.getCompilerOptions().getOutDir() == null) {
+            // no outDir specified, so skip this tsconfig.json
+            continue;
+          }
+          Path odir = cfg.getParent().resolve(root.getCompilerOptions().getOutDir()).toAbsolutePath().normalize();
+          outDirs.add(odir);
+        }
+      } catch (Exception e) {
+        // ignore malformed tsconfig or missing fields
+      }
+    }
+    // exclude files in output directories as configured in tsconfig.json
+    filesToExtract.removeIf(f -> outDirs.stream().anyMatch(od -> f.startsWith(od)));
 
     DependencyInstallationResult dependencyInstallationResult = DependencyInstallationResult.empty;
     if (!tsconfigFiles.isEmpty()) {
@@ -796,9 +818,19 @@ private CompletableFuture<?> extractFiles(
    */
   private boolean isFileDerivedFromTypeScriptFile(Path path, Set<Path> extractedFiles) {
     String name = path.getFileName().toString();
-    if (!name.endsWith(".js"))
+    // only skip JS variants when a corresponding TS/TSX file was already extracted
+    if (!(name.endsWith(".js")
+          || name.endsWith(".cjs")
+          || name.endsWith(".mjs")
+          || name.endsWith(".jsx")
+          || name.endsWith(".cjsx")
+          || name.endsWith(".mjsx"))) {
       return false;
-    String stem = name.substring(0, name.length() - ".js".length());
+    }
+    // strip off extension
+    int dot = name.lastIndexOf('.');
+    String stem = dot != -1 ? name.substring(0, dot) : name;
+    // if a TS/TSX file with same base name was extracted, skip this file
     for (String ext : FileType.TYPESCRIPT.getExtensions()) {
       if (extractedFiles.contains(path.getParent().resolve(stem + ext))) {
         return true;
@@ -1154,7 +1186,7 @@ public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
             }
 
             // extract TypeScript projects from 'tsconfig.json'
-            if (typeScriptMode == TypeScriptMode.FULL
+            if (typeScriptMode != TypeScriptMode.NONE
                 && treatAsTSConfig(file.getFileName().toString())
                 && !excludes.contains(file)
                 && isFileIncluded(file)) {

javascript/extractor/test/com/semmle/js/extractor/test/AutoBuildTests.java

@@ -135,6 +135,7 @@ public void extractTypeScriptFiles(
             FileExtractors extractors) {
           for (Path f : files) {
             actual.add(f.toString());
+            extractedFiles.add(f);
           }
         }
 
@@ -175,7 +176,7 @@ public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
 
   @Test
   public void basicTest() throws IOException {
-    addFile(true, LGTM_SRC, "tst.js");
+    addFile(false, LGTM_SRC, "tst.js");
     addFile(true, LGTM_SRC, "tst.ts");
     addFile(true, LGTM_SRC, "tst.html");
     addFile(true, LGTM_SRC, "tst.xsjs");
@@ -203,6 +204,43 @@ public void typescriptWrongConfig() throws IOException {
     runTest();
   }
 
+  @Test
+  public void skipJsFilesDerivedFromTypeScriptFiles() throws IOException {
+    // JS-derived files (.js, .cjs, .mjs, .jsx, .cjsx, .mjsx) should be skipped when TS indexing
+    envVars.put("LGTM_INDEX_TYPESCRIPT", "basic");
+    // Add TypeScript sources
+    addFile(true, LGTM_SRC, "foo.ts");
+    addFile(true, LGTM_SRC, "bar.tsx");
+    // Add derived JS variants (should be skipped)
+    addFile(false, LGTM_SRC, "foo.js");
+    addFile(false, LGTM_SRC, "bar.jsx");
+    addFile(false, LGTM_SRC, "foo.cjs");
+    addFile(false, LGTM_SRC, "foo.mjs");
+    addFile(false, LGTM_SRC, "bar.cjsx");
+    addFile(false, LGTM_SRC, "bar.mjsx");
+    // A normal JS file without TS counterpart should be extracted
+    addFile(true, LGTM_SRC, "normal.js");
+    runTest();
+  }
+
+  @Test
+  public void skipFilesInTsconfigOutDir() throws IOException {
+    envVars.put("LGTM_INDEX_TYPESCRIPT", "basic");
+    // Files under outDir in tsconfig.json should be excluded
+    // Create tsconfig.json with outDir set to "dist"
+    addFile(true, LGTM_SRC, "tsconfig.json");
+    Path config = Paths.get(LGTM_SRC.toString(), "tsconfig.json");
+    Files.write(config,
+        "{\"compilerOptions\":{\"outDir\":\"dist\"}}".getBytes(StandardCharsets.UTF_8));
+    // Add files outside outDir (should be extracted)
+    addFile(true, LGTM_SRC, "src", "app.ts");
+    addFile(true, LGTM_SRC, "main.js");
+    // Add files under dist/outDir (should be skipped)
+    addFile(false, LGTM_SRC, "dist", "generated.js");
+    addFile(false, LGTM_SRC, "dist", "sub", "x.js");
+    runTest();
+  }
+
   @Test
   public void includeFile() throws IOException {
     envVars.put("LGTM_INDEX_INCLUDE", "tst.js");

javascript/ql/lib/change-notes/2025-06-05-skip-obviously-generated-files.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The JavaScript extractor now skips generated JavaScript files if the original TypeScript files are already present. It also skips any files in the output directory specified in the `compilerOptions` part of the `tsconfig.json` file.