fix(@ngtools/webpack): directly use single path mappings

Author: clydin

packages/@ngtools/webpack/src/paths-plugin.ts

@@ -14,7 +14,7 @@ export function resolveWithPaths(
   host: ts.CompilerHost,
   cache?: ts.ModuleResolutionCache,
 ) {
-  if (!request || !request.request) {
+  if (!request || !request.request || !compilerOptions.paths) {
     callback(null, request);
     return;
   }
@@ -26,21 +26,54 @@ export function resolveWithPaths(
   }
 
   // check if any path mapping rules are relevant
-  const isPathMapped = compilerOptions.paths && Object.keys(compilerOptions.paths)
-    .some(pattern => {
+  const pathMapOptions = [];
+  for (const pattern in compilerOptions.paths) {
       // can only contain zero or one
       const starIndex = pattern.indexOf('*');
       if (starIndex === -1) {
-        return pattern === request.request;
+        if (pattern === request.request) {
+          pathMapOptions.push({
+            partial: '',
+            potentials: compilerOptions.paths[pattern]
+          });
+        }
       } else if (starIndex === pattern.length - 1) {
-        return request.request.startsWith(pattern.slice(0, -1));
+        if (request.request.startsWith(pattern.slice(0, -1))) {
+          pathMapOptions.push({
+            partial: request.request.slice(pattern.length - 1),
+            potentials: compilerOptions.paths[pattern]
+          });
+        }
       } else {
         const [prefix, suffix] = pattern.split('*');
-        return request.request.startsWith(prefix) && request.request.endsWith(suffix);
+        if (request.request.startsWith(prefix) && request.request.endsWith(suffix)) {
+          pathMapOptions.push({
+            partial: request.request.slice(prefix.length).slice(0, -suffix.length),
+            potentials: compilerOptions.paths[pattern]
+          });
+        }
       }
-    });
+  }
+
+  if (pathMapOptions.length === 0) {
+    callback(null, request);
+    return;
+  }
+
+  if (pathMapOptions.length === 1 && pathMapOptions[0].potentials.length === 1) {
+    const onlyPotential = pathMapOptions[0].potentials[0];
+    let replacement;
+    const starIndex = onlyPotential.indexOf('*');
+    if (starIndex === -1) {
+      replacement = onlyPotential;
+    } else if (starIndex === onlyPotential.length - 1) {
+      replacement = onlyPotential.slice(0, -1) + pathMapOptions[0].partial;
+    } else {
+      const [prefix, suffix] = onlyPotential.split('*');
+      replacement = prefix + pathMapOptions[0].partial + suffix;
+    }
 
-  if (!isPathMapped) {
+    request.request = path.resolve(compilerOptions.baseUrl, replacement);
     callback(null, request);
     return;
   }

tests/e2e/tests/misc/module-resolution.ts

@@ -1,10 +1,29 @@
-import { appendToFile, prependToFile } from '../../utils/fs';
+import { appendToFile, createDir, moveFile, prependToFile } from '../../utils/fs';
 import { ng, silentNpm } from '../../utils/process';
 import { updateJsonFile } from '../../utils/project';
 import { expectToFail } from '../../utils/utils';
 
 
 export default async function () {
+  await createDir('xyz');
+  await moveFile(
+    'node_modules/@angular/common',
+    'xyz/common'
+  );
+
+  await expectToFail(() => ng('build'));
+
+  await updateJsonFile('src/tsconfig.app.json', tsconfig => {
+    tsconfig.compilerOptions.paths = {
+      '@angular/common': [ '../xyz/common' ],
+    };
+  });
+  await ng('build');
+
+  await updateJsonFile('src/tsconfig.app.json', tsconfig => {
+    delete tsconfig.compilerOptions.paths;
+  });
+
   await prependToFile('src/app/app.module.ts', 'import * as firebase from \'firebase\';');
   await appendToFile('src/app/app.module.ts', 'firebase.initializeApp({});');
 
@@ -16,10 +35,6 @@ export default async function () {
   await ng('build', '--aot');
   await ng('test', '--single-run');
 
-  // await prependToFile('src/app/app.module.ts', 'import * as firebase from \'firebase\';');
-  // await appendToFile('src/app/app.module.ts', 'firebase.initializeApp({});');
-  // await ng('build');
-
   await updateJsonFile('src/tsconfig.app.json', tsconfig => {
     tsconfig.compilerOptions.paths = {};
   });