80b1ba9f95
This interface now extends `ReadonlyFileSystem` which in turn extends `PathManipulation`. This means consumers of these interfaces can be more specific about what is needed, and so providers do not need to implement unnecessary methods. PR Close #40281
56 lines
2.7 KiB
Markdown
56 lines
2.7 KiB
Markdown
# Virtual file-system layer
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To improve cross platform support, all file access (and path manipulation)
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is now done through a well known interface (`FileSystem`).
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Note that `FileSystem` extends `ReadonlyFileSystem`, which itself extends
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`PathManipulation`.
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If you are using a file-system object you should only ask for the type that supports
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all the methods that you require.
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For example, if you have a function (`foo()`) that only needs to resolve paths then
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it should only require `PathManipulation`: `foo(fs: PathManipulation)`.
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This allows the caller to avoid implementing unneeded functionality.
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For testing, a number of `MockFileSystem` implementations are supplied.
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These provide an in-memory file-system which emulates operating systems
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like OS/X, Unix and Windows.
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The current file system is always available via the helper method,
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`getFileSystem()`. This is also used by a number of helper
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methods to avoid having to pass `FileSystem` objects around all the time.
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The result of this is that one must be careful to ensure that the file-system
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has been initialized before using any of these helper methods.
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To prevent this happening accidentally the current file system always starts out
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as an instance of `InvalidFileSystem`, which will throw an error if any of its
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methods are called.
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Generally it is safer to explicitly pass file-system objects to constructors or
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free-standing functions if possible. This avoids confusing bugs where the
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global file-system has not been set-up correctly before calling functions that
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expect there to be a file-system configured globally.
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You can set the current file-system by calling `setFileSystem()`.
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During testing you can call the helper function `initMockFileSystem(os)`
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which takes a string name of the OS to emulate, and will also monkey-patch
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aspects of the TypeScript library to ensure that TS is also using the
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current file-system.
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Finally there is the `NgtscCompilerHost` to be used for any TypeScript
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compilation, which uses a given file-system.
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All tests that interact with the file-system should be tested against each
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of the mock file-systems. A series of helpers have been provided to support
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such tests:
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* `runInEachFileSystem()` - wrap your tests in this helper to run all the
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wrapped tests in each of the mock file-systems, it calls `initMockFileSystem()`
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for each OS to emulate.
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* `loadTestFiles()` - use this to add files and their contents
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to the mock file system for testing.
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* `loadStandardTestFiles()` - use this to load a mirror image of files on
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disk into the in-memory mock file-system.
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* `loadFakeCore()` - use this to load a fake version of `@angular/core`
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into the mock file-system.
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All ngcc and ngtsc source and tests now use this virtual file-system setup.
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