fix(ivy): ngcc - capture entry-points in top-level path-mapped folders

The `EntryPointFinder` computes the base paths to consider
when searching for entry-points. When there are `pathMappings`
provided it works out the best top level base-paths that cover all
the potential mappings.

If this computed basePath happens to coincide with an entry-point
path itself then we were missing it.

Now we check for an entry-point even at the base-path itself.

Related to angular/angular-cli#14755

Author: petebacondarwin

packages/compiler-cli/ngcc/src/packages/entry_point_finder.ts

@@ -70,7 +70,12 @@ export class EntryPointFinder {
    * @param sourceDirectory An absolute path to the root directory where searching begins.
    */
   private walkDirectoryForEntryPoints(sourceDirectory: AbsoluteFsPath): EntryPoint[] {
-    const entryPoints: EntryPoint[] = [];
+    const entryPoints = this.getEntryPointsForPackage(sourceDirectory);
+    if (entryPoints.length > 0) {
+      // The `sourceDirectory` is an entry-point itself so no need to search its sub-directories.
+      return entryPoints;
+    }
+
     this.fs
         .readdir(sourceDirectory)
         // Not interested in hidden files
@@ -86,16 +91,12 @@ export class EntryPointFinder {
           // Either the directory is a potential package or a namespace containing packages (e.g
           // `@angular`).
           const packagePath = AbsoluteFsPath.join(sourceDirectory, p);
-          if (p.startsWith('@')) {
-            entryPoints.push(...this.walkDirectoryForEntryPoints(packagePath));
-          } else {
-            entryPoints.push(...this.getEntryPointsForPackage(packagePath));
+          entryPoints.push(...this.walkDirectoryForEntryPoints(packagePath));
 
-            // Also check for any nested node_modules in this package
-            const nestedNodeModulesPath = AbsoluteFsPath.join(packagePath, 'node_modules');
-            if (this.fs.exists(nestedNodeModulesPath)) {
-              entryPoints.push(...this.walkDirectoryForEntryPoints(nestedNodeModulesPath));
-            }
+          // Also check for any nested node_modules in this package
+          const nestedNodeModulesPath = AbsoluteFsPath.join(packagePath, 'node_modules');
+          if (this.fs.exists(nestedNodeModulesPath)) {
+            entryPoints.push(...this.walkDirectoryForEntryPoints(nestedNodeModulesPath));
           }
         });
     return entryPoints;
@@ -111,11 +112,14 @@ export class EntryPointFinder {
 
     // Try to get an entry point from the top level package directory
     const topLevelEntryPoint = getEntryPointInfo(this.fs, this.logger, packagePath, packagePath);
-    if (topLevelEntryPoint !== null) {
-      entryPoints.push(topLevelEntryPoint);
+
+    // If there is no primary entry-point then exit
+    if (topLevelEntryPoint === null) {
+      return [];
     }
 
-    // Now search all the directories of this package for possible entry points
+    // Otherwise store it and search for secondary entry-points
+    entryPoints.push(topLevelEntryPoint);
     this.walkDirectory(packagePath, subdir => {
       const subEntryPoint = getEntryPointInfo(this.fs, this.logger, packagePath, subdir);
       if (subEntryPoint !== null) {

packages/compiler-cli/ngcc/test/packages/entry_point_finder_spec.ts

@@ -52,6 +52,21 @@ describe('findEntryPoints()', () => {
     ]);
   });
 
+  it('should find entry-points via `pathMappings', () => {
+    const {entryPoints} = finder.findEntryPoints(
+        _('/pathMappings/node_modules'), undefined,
+        {baseUrl: _('/pathMappings'), paths: {'my-lib': ['dist/my-lib']}});
+    const entryPointPaths = entryPoints.map(x => [x.package, x.path]);
+    expect(entryPointPaths).toEqual([
+      [_('/pathMappings/dist/my-lib'), _('/pathMappings/dist/my-lib')],
+      [_('/pathMappings/dist/my-lib'), _('/pathMappings/dist/my-lib/sub-lib')],
+      [
+        _('/pathMappings/node_modules/@angular/common'),
+        _('/pathMappings/node_modules/@angular/common')
+      ],
+    ]);
+  });
+
   it('should return an empty array if there are no packages', () => {
     const {entryPoints} = finder.findEntryPoints(_('/no_packages'));
     expect(entryPoints).toEqual([]);
@@ -105,6 +120,26 @@ describe('findEntryPoints()', () => {
           },
         },
       },
+      '/pathMappings': {
+        'dist': {
+          'my-lib': {
+            'package.json': createPackageJson('my-lib'),
+            'my-lib.metadata.json': 'metadata info',
+            'sub-lib': {
+              'package.json': createPackageJson('sub-lib'),
+              'sub-lib.metadata.json': 'metadata info',
+            },
+          },
+        },
+        'node_modules': {
+          '@angular': {
+            'common': {
+              'package.json': createPackageJson('common'),
+              'common.metadata.json': 'metadata info',
+            },
+          },
+        }
+      },
       '/namespaced': {
         '@angular': {
           'common': {