fix(compiler): report an error for recursive module references

Modules that directly or indirectly export or imported themselves
reports an error instead of generating a stack fault.

Fixes: #19979

packages/compiler-cli/test/ngc_spec.ts

@@ -1636,6 +1636,68 @@ describe('ngc transformer command-line', () => {
       expect(messages[0]).toContain('Parser Error: Unexpected token');
     });
 
+    // Regression test for #19979
+    it('should not stack overflow on a recursive module export', () => {
+      write('src/tsconfig.json', `{
+        "extends": "../tsconfig-base.json",
+        "files": ["test-module.ts"]
+      }`);
+
+      write('src/test-module.ts', `
+        import {Component, NgModule} from '@angular/core';
+
+        @Component({
+          template: 'Hello'
+        })
+        export class MyFaultyComponent {}
+
+        @NgModule({
+          exports: [MyFaultyModule],
+          declarations: [MyFaultyComponent],
+          providers: [],
+        })
+        export class MyFaultyModule { }
+      `);
+      const messages: string[] = [];
+      expect(
+          main(['-p', path.join(basePath, 'src/tsconfig.json')], message => messages.push(message)))
+          .toBe(1, 'Compile was expected to fail');
+      expect(messages[0]).toContain(`module 'MyFaultyModule' is exported recursively`);
+    });
+
+    // Regression test for #19979
+    it('should not stack overflow on a recursive module import', () => {
+      write('src/tsconfig.json', `{
+        "extends": "../tsconfig-base.json",
+        "files": ["test-module.ts"]
+      }`);
+
+      write('src/test-module.ts', `
+        import {Component, NgModule, forwardRef} from '@angular/core';
+
+        @Component({
+          template: 'Hello'
+        })
+        export class MyFaultyComponent {}
+
+        @NgModule({
+          imports: [forwardRef(() => MyFaultyModule)]
+        })
+        export class MyFaultyImport {}
+
+        @NgModule({
+          imports: [MyFaultyImport],
+          declarations: [MyFaultyComponent]
+        })
+        export class MyFaultyModule { }
+      `);
+      const messages: string[] = [];
+      expect(
+          main(['-p', path.join(basePath, 'src/tsconfig.json')], message => messages.push(message)))
+          .toBe(1, 'Compile was expected to fail');
+      expect(messages[0]).toContain(`is imported recursively by the module 'MyFaultyImport`);
+    });
+
     it('should allow using 2 classes with the same name in declarations with noEmitOnError=true',
        () => {
          write('src/tsconfig.json', `{

packages/compiler/src/metadata_resolver.ts

@@ -444,11 +444,12 @@ export class CompileMetadataResolver {
         this._ngModuleResolver.isNgModule(type);
   }
 
-  getNgModuleSummary(moduleType: any): cpl.CompileNgModuleSummary|null {
+  getNgModuleSummary(moduleType: any, alreadyCollecting: Set<any>|null = null):
+      cpl.CompileNgModuleSummary|null {
     let moduleSummary: cpl.CompileNgModuleSummary|null =
         <cpl.CompileNgModuleSummary>this._loadSummary(moduleType, cpl.CompileSummaryKind.NgModule);
     if (!moduleSummary) {
-      const moduleMeta = this.getNgModuleMetadata(moduleType, false);
+      const moduleMeta = this.getNgModuleMetadata(moduleType, false, alreadyCollecting);
       moduleSummary = moduleMeta ? moduleMeta.toSummary() : null;
       if (moduleSummary) {
         this._summaryCache.set(moduleType, moduleSummary);
@@ -476,7 +477,9 @@ export class CompileMetadataResolver {
     return Promise.all(loading);
   }
 
-  getNgModuleMetadata(moduleType: any, throwIfNotFound = true): cpl.CompileNgModuleMetadata|null {
+  getNgModuleMetadata(
+      moduleType: any, throwIfNotFound = true,
+      alreadyCollecting: Set<any>|null = null): cpl.CompileNgModuleMetadata|null {
     moduleType = resolveForwardRef(moduleType);
     let compileMeta = this._ngModuleCache.get(moduleType);
     if (compileMeta) {
@@ -514,7 +517,18 @@ export class CompileMetadataResolver {
 
         if (importedModuleType) {
           if (this._checkSelfImport(moduleType, importedModuleType)) return;
-          const importedModuleSummary = this.getNgModuleSummary(importedModuleType);
+          if (!alreadyCollecting) alreadyCollecting = new Set();
+          if (alreadyCollecting.has(importedModuleType)) {
+            this._reportError(
+                syntaxError(
+                    `${this._getTypeDescriptor(importedModuleType)} '${stringifyType(importedType)}' is imported recursively by the module '${stringifyType(moduleType)}'.`),
+                moduleType);
+            return;
+          }
+          alreadyCollecting.add(importedModuleType);
+          const importedModuleSummary =
+              this.getNgModuleSummary(importedModuleType, alreadyCollecting);
+          alreadyCollecting.delete(importedModuleType);
           if (!importedModuleSummary) {
             this._reportError(
                 syntaxError(
@@ -542,7 +556,17 @@ export class CompileMetadataResolver {
               moduleType);
           return;
         }
-        const exportedModuleSummary = this.getNgModuleSummary(exportedType);
+        if (!alreadyCollecting) alreadyCollecting = new Set();
+        if (alreadyCollecting.has(exportedType)) {
+          this._reportError(
+              syntaxError(
+                  `${this._getTypeDescriptor(exportedType)} '${stringify(exportedType)}' is exported recursively by the module '${stringifyType(moduleType)}'`),
+              moduleType);
+          return;
+        }
+        alreadyCollecting.add(exportedType);
+        const exportedModuleSummary = this.getNgModuleSummary(exportedType, alreadyCollecting);
+        alreadyCollecting.delete(exportedType);
         if (exportedModuleSummary) {
           exportedModules.push(exportedModuleSummary);
         } else {