fix(@ngtools/webpack): when an error happens rediagnose the file

Before there was a bug that the file wasnt forced to rediagnose.

If the file changed, we wont diagnose it twice because we keep a hash table per compilation anyway.

Fixes angular#4810
Fixes angular#5404

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

@@ -410,6 +410,11 @@ export class AotPlugin implements Tapable {
         this._program = ts.createProgram(
           this._rootFilePath, this._compilerOptions, this._compilerHost, this._program);
       })
+      .then(() => {
+        // Re-diagnose changed files.
+        const changedFilePaths = this._compilerHost.getChangedFilePaths();
+        changedFilePaths.forEach(filePath => this.diagnose(filePath));
+      })
       .then(() => {
         if (this._typeCheck) {
           const diagnostics = this._program.getGlobalDiagnostics();
@@ -461,7 +466,9 @@ export class AotPlugin implements Tapable {
           });
       })
       .then(() => {
-        this._compilerHost.resetChangedFileTracker();
+        if (this._compilation.errors == 0) {
+          this._compilerHost.resetChangedFileTracker();
+        }
 
         cb();
       }, (err: any) => {

tests/e2e/tests/build/rebuild-deps-type-check.ts

@@ -40,7 +40,7 @@ export default function() {
     `))
     // Should trigger a rebuild, no error expected.
     .then(() => waitForAnyProcessOutputToMatch(doneRe, 10000))
-    // Create and import files.
+    // Make an invalid version of the file.
     .then(() => wait(2000))
     .then(() => writeFile('src/funky2.ts', `
       export function funky(value: number): number {
@@ -54,6 +54,18 @@ export default function() {
         throw new Error('Expected an error but none happened.');
       }
     })
+    // Change an UNRELATED file and the error should still happen.
+    .then(() => wait(2000))
+    .then(() => appendToFile('src/app/app.module.ts', `
+      function anything(): number {}
+    `))
+    // Should trigger a rebuild, this time an error is expected.
+    .then(() => waitForAnyProcessOutputToMatch(doneRe, 10000))
+    .then(({ stdout }) => {
+      if (!/ERROR in .*\/src\/main\.ts \(/.test(stdout)) {
+        throw new Error('Expected an error but none happened.');
+      }
+    })
     // Fix the error!
     .then(() => writeFile('src/funky2.ts', `
       export function funky(value: string): string {