UNPKG

@angular/compiler-cli

Version:

Angular - the compiler CLI for Node.js

github.com/angular/angular/tree/main/packages/compiler-cli

angular/angular

69 lines (68 loc) • 4.42 kB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
/** * @license * Copyright Google LLC All Rights Reserved. * * Use of this source code is governed by an MIT-style license that can be * found in the LICENSE file at https://angular.dev/license */ import ts from 'typescript'; /** Possible alias import declarations */ export type AliasImportDeclaration = ts.ImportSpecifier | ts.NamespaceImport | ts.ImportClause; /** * Patches the alias declaration reference resolution for a given transformation context * so that TypeScript knows about the specified alias declarations being referenced. * * This exists because TypeScript performs analysis of import usage before transformers * run and doesn't refresh its state after transformations. This means that imports * for symbols used as constructor types are elided due to their original type-only usage. * * In reality though, since we downlevel decorators and constructor parameters, we want * these symbols to be retained in the JavaScript output as they will be used as values * at runtime. We can instruct TypeScript to preserve imports for such identifiers by * creating a mutable clone of a given import specifier/clause or namespace, but that * has the downside of preserving the full import in the JS output. See: * https://github.com/microsoft/TypeScript/blob/3eaa7c65f6f076a08a5f7f1946fd0df7c7430259/src/compiler/transformers/ts.ts#L242-L250. * * This is a trick the CLI used in the past for constructor parameter downleveling in JIT: * https://github.com/angular/angular-cli/blob/b3f84cc5184337666ce61c07b7b9df418030106f/packages/ngtools/webpack/src/transformers/ctor-parameters.ts#L323-L325 * The trick is not ideal though as it preserves the full import (as outlined before), and it * results in a slow-down due to the type checker being involved multiple times. The CLI worked * around this import preserving issue by having another complex post-process step that detects and * elides unused imports. Note that these unused imports could cause unused chunks being generated * by webpack if the application or library is not marked as side-effect free. * * This is not ideal though, as we basically re-implement the complex import usage resolution * from TypeScript. We can do better by letting TypeScript do the import eliding, but providing * information about the alias declarations (e.g. import specifiers) that should not be elided * because they are actually referenced (as they will now appear in static properties). * * More information about these limitations with transformers can be found in: * 1. https://github.com/Microsoft/TypeScript/issues/17552. * 2. https://github.com/microsoft/TypeScript/issues/17516. * 3. https://github.com/angular/tsickle/issues/635. * * The patch we apply to tell TypeScript about actual referenced aliases (i.e. imported symbols), * matches conceptually with the logic that runs internally in TypeScript when the * `emitDecoratorMetadata` flag is enabled. TypeScript basically surfaces the same problem and * solves it conceptually the same way, but obviously doesn't need to access an internal API. * * The set that is returned by this function is meant to be filled with import declaration nodes * that have been referenced in a value-position by the transform, such the installed patch can * ensure that those import declarations are not elided. * * If `null` is returned then the transform operates in an isolated context, i.e. using the * `ts.transform` API. In such scenario there is no information whether an alias declaration * is referenced, so all alias declarations are naturally preserved and explicitly registering * an alias declaration as used isn't necessary. * * See below. Note that this uses sourcegraph as the TypeScript checker file doesn't display on * Github. * https://sourcegraph.com/github.com/microsoft/TypeScript@3eaa7c65f6f076a08a5f7f1946fd0df7c7430259/-/blob/src/compiler/checker.ts#L31219-31257 */ export declare function loadIsReferencedAliasDeclarationPatch(context: ts.TransformationContext): Set<ts.Declaration> | null; /** * Gets whether a given node corresponds to an import alias declaration. Alias * declarations can be import specifiers, namespace imports or import clauses * as these do not declare an actual symbol but just point to a target declaration. */ export declare function isAliasImportDeclaration(node: ts.Node): node is AliasImportDeclaration;