Utilize the TypeScript Compiler API to extract the Type Alias Declaration Node from a Type Reference Node

Currently, I am utilizing ts-morph library which makes use of the TS Compiler API.

Here is an example of my code:

export type Foo = string
export const foo: Foo = 'bar'

Whenever I try to find the type for the export of foo, it returns string. However, what I actually need is the type alias declaration type.

The Node type of the export foo is a VariableDeclaration. Through this, I discovered a way to reach the TypeReferenceNode. Once there, I found a method to retrieve the name of the reference, such as "Foo". But, I am unsure how to progress from this name to locate the type alias declaration. Let's assume we are unaware of where the "Foo" type alias is located. How can this be determined dynamically?

typescripttsctypescript-compiler-api

Answer №1

In this particular scenario, it's not feasible. The TypeScript compiler opts to intern certain types for performance enhancements.

Certain types are internally stored for efficiency reasons (to prevent redundant work on equivalent types). While anonymous object types are not currently interned, there have been experiments with it in the past. However, interning object types can disrupt the go-to-definition feature on those types, so it was ultimately not implemented. Indexed accesses, unions, intersections, and reverse mapped types (through inference) are the types that are currently interned. This decision comes with a tradeoff - losing original information on interned types, but saving computational resources most of the time. - Source

Here, Foo is being stored as string due to their equivalence. I reached out in the TypeScript repository to inquire about disabling this behavior for analytical purposes, but have yet to receive a response.

If you want to overcome this obstacle, you can modify the code to incorporate a brand alongside string.

export type Foo = string & { __FooBrand?: undefined };
export const foo: Foo = 'bar';

For further reference, check out these links:

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