CODEWITHSUNDEEP
typescripttypescript-compiler-api
Dor Ben Baruch
Dor Ben Baruch

Reputation: 215

Generating type declaration from import url using the TypeScript compiler API

I'm trying to generate some type declarations for a project. The main idea here is that I got to a point where I am able to generate something like this:

type T = typeof import("somepath").default

Where default is a function.

The code that does this is:

ts.createTypeAliasDeclaration(
  undefined,
  undefined,
  ts.createIdentifier("T"),
  undefined,
  ts.createTypeOf(
    ts.createPropertyAccess(
      ts.createCall(
        ts.createToken(ts.SyntaxKind.ImportKeyword),
        undefined,
        [ts.createStringLiteral("somepath")]
      ), 
      ts.createIdentifier("default"))
    ),
    undefined,
    true
);

After printing that to the console I can see the output of that is indeed:

type T = typeof import("somepath").default

Now I have a variable, say t that holds the node of that type alias declaration, but when I try to extract the type with the type checker I keep getting any. So far I've tried checker.getTypeAtLocation and checker.getTypeFromTypeNode but I keep getting any no matter what I try (I checked manually and vscode can indeed verify the type is not any).

Any help would be much appreciated, Thanks!

Upvotes: 1

Views: 663

Answers (1)

David Sherret
David Sherret

Reputation: 106650

The TypeScript compiler was designed to do type checking before transformation and so for the most part the type checker assumes the node it's type checking will be contained in a source file node and that the source file's text will match the descendant AST nodes (there's some internal data that gets set on nodes when parsing text to a source file).

You can make this work by printing out the node to text (using ts.createPrinter), reparsing it in a source file (ts.createSourceFile... or updating an existing source file with the update method), getting a reference to the parsed T type alias node, then using that source file in a new program to get a new type checker. It's a lot of code, so it would be too much work to post it here.

Upvotes: 1

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