Start using a union for FunctionLike things #16988
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sandersn
approved these changes
Jul 6, 2017
src/compiler/types.ts
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| | SetAccessorDeclaration | ||
| | FunctionExpression | ||
| | ArrowFunction; | ||
| export type FunctionLikeTypes = |
ghost
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We have a type,
FunctionLikeDeclaration, which is used a lot internally. We also have a functionisFunctionLikewhich, prior to this PR, guarded to that type. However, what the type guard checked for and what was based on that type were not the same set of types. This PR clarifies the relationship between what that guard checks for and what is considered aFunctionLikeDeclarationby moving everything over to using unions of the correct types (isFunctionLikenow guards to a union of the type associated with the syntax kinds it actually checks) - this has the added advantage that in places where usage is correct, fewer casts are required. (Although, in many cases we unsafely check ifnode.bodyexists when the node's type indicates it should never have a body - in these places we now need a cast to assert that we'd like to check the potentially nonexistent property)It also breaks the property signature interface into two interfaces so they may be union-ed together and properly discriminated in our current checker.
I mentioned I had done this in one of my branches to @sandersn as I was working because I was becoming annoyed by lots of small gotchyas when attempting to use these types as they existed prior (and attempting to remember what was/was not safe to cast to).