如何使用 TypeScript Compiler API 查找环境模块声明的定义位置？

Question

If something is defined in an ambient module declaration in another file:

declare module "@foo" {
    export default function func(): number;
}

and use the module:

import func from "@foo";

How can I use the TS Compiler API to find out where func is defined?

Normally, for figuring out where imports come from, I use ts.resolveModuleName , but it always returns undefined in this case.

Answer 1

This is possible by following the symbols to the declaration.

1. Get the func identifier node.
2. Get its symbol, which will be local to the current file.
3. Get the aliased symbol of that symbol, which will be the symbol of the declaration.
4. Get that aliased symbol's declaration, which will be the function declaration.

Here's a contained example:

// setup
import { createProjectSync, ts } from "@ts-morph/bootstrap";

const project = createProjectSync();
project.createSourceFile("foo.d.ts", `declare module "@foo" { export default function func(): number; }`);
const sourceFile = project.createSourceFile("file.ts", `import func from "@foo";`);
const typeChecker = project.createProgram().getTypeChecker();

// get the "func" identifier in the import declaration
const importDec = sourceFile.statements[0] as ts.ImportDeclaration;
const funcIdent = importDec.importClause!.name!;

// follow the symbols to the function declaration
const funcImportSymbol = typeChecker.getSymbolAtLocation(funcIdent)!;
const funcDecSymbol = typeChecker.getAliasedSymbol(funcImportSymbol);
const funcDec = funcDecSymbol.getDeclarations()![0];

console.log(funcDec.getText());

Also, for getting the source file referenced in a module specifier, I still recommend getting the module specifier's symbol instead of using ts.resolveModuleName as outlined in this answer .