refactor(ivy): extract import rewriting into a separate interface (#27998)

Currently the ImportManager class handles various rewriting actions of
imports when compiling @angular/core. This is required as code compiled
within @angular/core cannot import from '@angular/core'. To work around
this, imports are rewritten to get core symbols from a particular file,
r3_symbols.ts.

In this refactoring, this rewriting logic is moved out of the ImportManager
and put behind an interface, ImportRewriter. There are three implementers
of the interface:

* NoopImportRewriter, used for compiling all non-core packages.
* R3SymbolsImportRewriter, used when ngtsc compiles @angular/core.
* NgccFlatImportRewriter, used when ngcc compiles @angular/core (special
  logic is needed because ngcc has to rewrite imports in flat bundles
  differently than in non-flat bundles).

This is a precursor to using this rewriting logic in other contexts besides
the ImportManager.

PR Close #27998

packages/compiler-cli/src/ngtsc/transform/BUILD.bazel

@@ -12,6 +12,7 @@ ts_library(
     deps = [
         "//packages/compiler",
         "//packages/compiler-cli/src/ngtsc/diagnostics",
+        "//packages/compiler-cli/src/ngtsc/imports",
         "//packages/compiler-cli/src/ngtsc/reflection",
         "//packages/compiler-cli/src/ngtsc/translator",
         "//packages/compiler-cli/src/ngtsc/typecheck",

packages/compiler-cli/src/ngtsc/transform/src/compilation.ts

@@ -10,6 +10,7 @@ import {ConstantPool} from '@angular/compiler';
 import * as ts from 'typescript';
 
 import {FatalDiagnosticError} from '../../diagnostics';
+import {ImportRewriter} from '../../imports';
 import {Decorator, ReflectionHost, reflectNameOfDeclaration} from '../../reflection';
 import {TypeCheckContext} from '../../typecheck';
 
@@ -17,6 +18,7 @@ import {AnalysisOutput, CompileResult, DecoratorHandler} from './api';
 import {DtsFileTransformer} from './declaration';
 
 
+
 /**
  * Record of an adapter which decided to emit a static field, and the analysis it performed to
  * prepare for that operation.
@@ -63,7 +65,7 @@ export class IvyCompilation {
    */
   constructor(
       private handlers: DecoratorHandler<any, any>[], private checker: ts.TypeChecker,
-      private reflector: ReflectionHost, private coreImportsFrom: ts.SourceFile|null,
+      private reflector: ReflectionHost, private importRewriter: ImportRewriter,
       private sourceToFactorySymbols: Map<string, Set<string>>|null) {}
 
 
@@ -227,7 +229,7 @@ export class IvyCompilation {
 
   private getDtsTransformer(tsFileName: string): DtsFileTransformer {
     if (!this.dtsMap.has(tsFileName)) {
-      this.dtsMap.set(tsFileName, new DtsFileTransformer(this.coreImportsFrom));
+      this.dtsMap.set(tsFileName, new DtsFileTransformer(this.importRewriter));
     }
     return this.dtsMap.get(tsFileName) !;
   }

packages/compiler-cli/src/ngtsc/transform/src/declaration.ts

@@ -8,6 +8,7 @@
 
 import * as ts from 'typescript';
 
+import {ImportRewriter} from '../../imports';
 import {ImportManager, translateType} from '../../translator';
 
 import {CompileResult} from './api';
@@ -21,8 +22,8 @@ export class DtsFileTransformer {
   private ivyFields = new Map<string, CompileResult[]>();
   private imports: ImportManager;
 
-  constructor(private coreImportsFrom: ts.SourceFile|null, importPrefix?: string) {
-    this.imports = new ImportManager(coreImportsFrom !== null, importPrefix);
+  constructor(private importRewriter: ImportRewriter, importPrefix?: string) {
+    this.imports = new ImportManager(importRewriter, importPrefix);
   }
 
   /**
@@ -56,7 +57,7 @@ export class DtsFileTransformer {
       }
     }
 
-    const imports = this.imports.getAllImports(tsPath, this.coreImportsFrom);
+    const imports = this.imports.getAllImports(tsPath);
     if (imports.length !== 0) {
       dts = imports.map(i => `import * as ${i.as} from '${i.name}';\n`).join('') + dts;
     }

packages/compiler-cli/src/ngtsc/transform/src/transform.ts

@@ -9,6 +9,7 @@
 import {ConstantPool} from '@angular/compiler';
 import * as ts from 'typescript';
 
+import {ImportRewriter} from '../../imports';
 import {Decorator, ReflectionHost} from '../../reflection';
 import {ImportManager, translateExpression, translateStatement} from '../../translator';
 import {VisitListEntryResult, Visitor, visit} from '../../util/src/visitor';
@@ -19,11 +20,11 @@ import {IvyCompilation} from './compilation';
 const NO_DECORATORS = new Set<ts.Decorator>();
 
 export function ivyTransformFactory(
-    compilation: IvyCompilation, reflector: ReflectionHost,
-    coreImportsFrom: ts.SourceFile | null): ts.TransformerFactory<ts.SourceFile> {
+    compilation: IvyCompilation, reflector: ReflectionHost, importRewriter: ImportRewriter,
+    isCore: boolean): ts.TransformerFactory<ts.SourceFile> {
   return (context: ts.TransformationContext): ts.Transformer<ts.SourceFile> => {
     return (file: ts.SourceFile): ts.SourceFile => {
-      return transformIvySourceFile(compilation, context, reflector, coreImportsFrom, file);
+      return transformIvySourceFile(compilation, context, reflector, importRewriter, isCore, file);
     };
   };
 }
@@ -188,13 +189,12 @@ class IvyVisitor extends Visitor {
  */
 function transformIvySourceFile(
     compilation: IvyCompilation, context: ts.TransformationContext, reflector: ReflectionHost,
-    coreImportsFrom: ts.SourceFile | null, file: ts.SourceFile): ts.SourceFile {
+    importRewriter: ImportRewriter, isCore: boolean, file: ts.SourceFile): ts.SourceFile {
   const constantPool = new ConstantPool();
-  const importManager = new ImportManager(coreImportsFrom !== null);
+  const importManager = new ImportManager(importRewriter);
 
   // Recursively scan through the AST and perform any updates requested by the IvyCompilation.
-  const visitor =
-      new IvyVisitor(compilation, reflector, importManager, coreImportsFrom !== null, constantPool);
+  const visitor = new IvyVisitor(compilation, reflector, importManager, isCore, constantPool);
   const sf = visit(file, visitor, context);
 
   // Generate the constant statements first, as they may involve adding additional imports
@@ -202,7 +202,7 @@ function transformIvySourceFile(
   const constants = constantPool.statements.map(stmt => translateStatement(stmt, importManager));
 
   // Generate the import statements to prepend.
-  const addedImports = importManager.getAllImports(file.fileName, coreImportsFrom).map(i => {
+  const addedImports = importManager.getAllImports(file.fileName).map(i => {
     return ts.createImportDeclaration(
         undefined, undefined,
         ts.createImportClause(undefined, ts.createNamespaceImport(ts.createIdentifier(i.as))),