43 lines
2.1 KiB
TypeScript
Executable file
43 lines
2.1 KiB
TypeScript
Executable file
/// <amd-module name="@angular/compiler-cli/ngcc/src/packages/patch_ts_expando_initializer" />
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/**
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* Consider the following ES5 code that may have been generated for a class:
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*
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* ```
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* var A = (function(){
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* function A() {}
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* return A;
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* }());
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* A.staticProp = true;
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* ```
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*
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* Here, TypeScript marks the symbol for "A" as a so-called "expando symbol", which causes
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* "staticProp" to be added as an export of the "A" symbol.
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*
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* In the example above, symbol "A" has been assigned some flags to indicate that it represents a
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* class. Due to this flag, the symbol is considered an expando symbol and as such, "staticProp" is
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* stored in `ts.Symbol.exports`.
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*
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* A problem arises when "A" is not at the top-level, i.e. in UMD bundles. In that case, the symbol
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* does not have the flag that marks the symbol as a class. Therefore, TypeScript inspects "A"'s
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* initializer expression, which is an IIFE in the above example. Unfortunately however, only IIFEs
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* of the form `(function(){})()` qualify as initializer for an "expando symbol"; the slightly
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* different form seen in the example above, `(function(){}())`, does not. This prevents the "A"
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* symbol from being considered an expando symbol, in turn preventing "staticProp" from being stored
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* in `ts.Symbol.exports`.
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*
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* The logic for identifying symbols as "expando symbols" can be found here:
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* https://github.com/microsoft/TypeScript/blob/v3.4.5/src/compiler/binder.ts#L2656-L2685
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*
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* Notice how the `getExpandoInitializer` function is available on the "ts" namespace in the
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* compiled bundle, so we are able to override this function to accommodate for the alternative
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* IIFE notation. The original implementation can be found at:
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* https://github.com/Microsoft/TypeScript/blob/v3.4.5/src/compiler/utilities.ts#L1864-L1887
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*
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* Issue tracked in https://github.com/microsoft/TypeScript/issues/31778
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*
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* @returns the function to pass to `restoreGetExpandoInitializer` to undo the patch, or null if
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* the issue is known to have been fixed.
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*/
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export declare function patchTsGetExpandoInitializer(): unknown;
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export declare function restoreGetExpandoInitializer(originalGetExpandoInitializer: unknown): void;
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