Throw an early error if API Extractor attempts to process non.d.ts files

Author: zelliott

apps/api-extractor/src/collector/Collector.ts

@@ -188,6 +188,8 @@ export class Collector {
       this.messageRouter.addCompilerDiagnostic(diagnostic);
     }
 
+    const sourceFiles: readonly ts.SourceFile[] = this.program.getSourceFiles();
+
     if (this.messageRouter.showDiagnostics) {
       this.messageRouter.logDiagnosticHeader('Root filenames');
       for (const fileName of this.program.getRootFileNames()) {
@@ -196,12 +198,25 @@ export class Collector {
       this.messageRouter.logDiagnosticFooter();
 
       this.messageRouter.logDiagnosticHeader('Files analyzed by compiler');
-      for (const sourceFile of this.program.getSourceFiles()) {
+      for (const sourceFile of sourceFiles) {
         this.messageRouter.logDiagnostic(sourceFile.fileName);
       }
       this.messageRouter.logDiagnosticFooter();
     }
 
+    // We can throw this error earlier in CompilerState.ts, but intentionally wait until after we've logged the
+    // associated diagnostic message above to make debugging easier for developers.
+    const badSourceFile: boolean = sourceFiles.some(
+      ({ fileName }) => !ExtractorConfig.hasDtsFileExtension(fileName)
+    );
+    if (badSourceFile) {
+      throw new Error(
+        'API Extractor expects to only process .d.ts files, but encountered non-.d.ts file(s).\n' +
+          'Run with the "--diagnostics" flag and inspect the "Files analyzed by compiler" to find the unexpected ' +
+          'file(s).'
+      );
+    }
+
     // Build the entry point
     const entryPointSourceFile: ts.SourceFile = this.workingPackage.entryPointSourceFile;
 

common/changes/@microsoft/api-extractor/better-ts-file-error_2022-04-10-00-42.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft/api-extractor",
+      "comment": "Throw an error early if API Extractor will attempt to process non-.d.ts files",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@microsoft/api-extractor"
+}