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getTypeParameters not working?

See original GitHub issue

We noticed on our doc tool work that generics extraction are broken in TS 4.2. I know TS 4.2 changes how aliases are handled a bit, so not surprised. But I’m not sure how to get type parameters now…

Maybe I’m missing something, probably, or maybe there is a bug in ts-morph? The main thing is that getTypeParameters doesn’t seem to work like it used to.

Describe the bug

Version: 4.2.2 TS + 10.0.2 ts-morph

To Reproduce

import * as tsm from 'ts-morph'
import { Project, ts } from 'ts-morph'

console.log(ts.version) // x.x.x <-- provide this

const project = new Project()
const sourceFile = project.createSourceFile(
    export type A = Record<string,string>


const all = [...sourceFile.getExportedDeclarations()]

all.forEach(([name, decs]) => {

  const dec = decs[0]!

  const t = dec.getType()

  console.log('type alias dec -> type -> text', t.getText())
  console.log('type alias dec -> type -> sym -> dec -> text', t.getSymbol()?.getDeclarations()[0]?.getText())

  if (tsm.Node.isTypeAliasDeclaration(dec)) {
    const tp = dec.getTypeParameters()
    console.log(`type alias dec type parameters: ${tp.length}`)

  const tr = dec.getChildrenOfKind(tsm.ts.SyntaxKind.TypeReference)[0]!

  console.log('type reference -> text', tr.getText())

  console.log('type reference -> type -> text', tr.getType().getText())

    'type reference -> type arguments -> text',
    tr.getTypeArguments().map((ta) => ta.getText()),

  console.log('type reference -> type name -> text', tr.getTypeName().getText())

  console.log('type referene -> type -> sym -> dec -> text', tr.getType().getSymbol()?.getDeclarations()[0]?.getText())

    'type referene -> type -> sym -> dec -> kindName',


export type A = Record<string,string>
type alias dec -> type -> text import("/Users/jasonkuhrt/projects/pakadev/paka/foobar").A
type alias dec -> type -> sym -> dec -> text {[P in K]:T;}
type alias dec type parameters: 0
type reference -> text Record<string,string>
type reference -> type -> text import("/Users/jasonkuhrt/projects/pakadev/paka/foobar").A
type reference -> type arguments -> text [ 'string', 'string' ]
type reference -> type name -> text Record
type referene -> type -> sym -> dec -> text {[P in K]:T;}
type referene -> type -> sym -> dec -> kindName MappedType

Expected behavior

Should be able to get type parameters of record via getTypeParameters.

Issue Analytics

  • State:closed
  • Created 3 years ago
  • Reactions:1
  • Comments:6 (2 by maintainers)

github_iconTop GitHub Comments

dsherretcommented, Feb 26, 2021

I looked at this a bit and I’m not sure. I see the change between TS 4.1 and 4.2 on

You may want to play around in the browser console with the checker object and node object to see if you’re about to figure it out.

dsherretcommented, Feb 26, 2021

What’s the expected behaviour here? getTypeParameters() on the declaration will return the type alias node’s type parameter declarations (so it works exclusively in the AST)

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