53 lines
2.0 KiB
Markdown
53 lines
2.0 KiB
Markdown
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# tslib Direct Dependency Migration
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## What does this migration do?
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If you have any libraries within your workspace, this migration will convert `tslib` peer dependencies to direct dependencies for the libraries.
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TypeScript uses the `tslib` package to provide common helper functions used in compiled TypeScript code.
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The `tslib` version is also updated to `2.0.0` to support TypeScript 3.9.
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Before:
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```json
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{
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"name": "my-lib",
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"version": "0.0.1",
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"peerDependencies": {
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"@angular/common": "^9.0.0",
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"@angular/core": "^9.0.0",
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"tslib": "^1.12.0"
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}
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}
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```
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After:
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```json
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{
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"name": "my-lib",
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"version": "0.0.1",
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"peerDependencies": {
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"@angular/common": "^9.0.0",
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"@angular/core": "^9.0.0"
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},
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"dependencies": {
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"tslib": "^2.0.0"
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}
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}
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```
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## Why is this migration necessary?
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The [`tslib`](https://github.com/Microsoft/tslib) is a runtime library for Typescript.
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The version of this library is bound to the version of the TypeScript compiler used to compile a library.
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Peer dependencies do not accurately represent this relationship between the runtime and the compiler.
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If `tslib` remained declared as a library peer dependency, it would be possible for some Angular workspaces to get into a state where the workspace could not satisfy `tslib` peer dependency requirements for multiple libraries, resulting in build-time or run-time errors.
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As of TypeScript 3.9 (used by Angular v10), `tslib` version of 2.x is required to build new applications.
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However, older libraries built with previous version of TypeScript and already published to npm might need `tslib` 1.x.
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This migration makes it possible for code depending on incompatible versions of the `tslib` runtime library to remain interoperable.
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## Do I still need `tslib` as a dependency in my workspace `package.json`?
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Yes.
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The `tslib` dependency declared in the `package.json` file of the workspace is used to build applications within this workspace, as well as run unit tests for workspace libraries, and is required.
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