API: expose getEffectiveTypeParameterDeclarations

[ajafff]

TypeScript Version: 2.9.0-dev.20180518

Search Terms:

Code

import * as ts from 'typescript';
function getTypeParameters(node: ts.DeclarationWithTypeParameters) {
 return node.typeParameters;
}

Expected behavior:

No compile error. This used to work in 2.9.0-rc

Actual behavior:

Property 'typeParameters' does not exist on type 'DeclarationWithTypeParameters'.
 Property 'typeParameters' does not exist on type 'JSDocTypedefTag'.

Playground Link: not possible

Related Issues:

caused by #23947 Nathan Shively-Sanders (@sandersn)

[mhegazy]

It does have type parameters, it is just not on typeParameters, it is somewhere in the same JSDoc comment..

Can you filter out JSDocTypedefTag in your usage?

[ajafff]

I initially reported it because it seemed unintuitive and maybe unintentional.

Filtering out the JSDoc stuff would fix the compile error, but I'm actually interested in those type parameters.

So this is now more a suggestion to expose getEffectiveTypeParameterDeclarations

[mhegazy]

So this is now more a suggestion to expose getEffectiveTypeParameterDeclarations

that makes sense. a PR would be appreciated.. Nathan Shively-Sanders (@sandersn) any concerns?

[sandersn]

2. It's a pitfall to expose both the typeParameters property and getEffectiveTypeParameterDeclarations.
3. The name is clunky.

Ideally we would have either

1. A single function named getTypeParameters so Klaus Meinhardt (@ajafff) doesn't even have to write it.
2. The parser or some other component would produce a facade for js type aliases that actually has a type parameters property, plus a pointer back to the original.

Non-ideally, we would
3. Expose getEffecitveTypeParmaeterDeclarations.

(1) would break existing users of the typeParameters property. (2) might or might not be feasible. I lean toward (3) but I'm not sure how bad the break of (1) is.

[ajafff]

Now that #24600 added more logic to getEffectiveTypeParameterDeclarations, I'm even more in the need of a public API for that purpose. I don't want to duplicate all that code.

[ajafff]

Nathan Shively-Sanders (@sandersn) any chance this will make it into the 3.0.0 release? Otherwise I will probably rebuild that logic as part of my library tsutils.

[sandersn]

Very high chance. However, the public API is temporarily broken because of the new build system, but that should be resolved in a day or two.

In the meantime, I assigned myself so I don't forget and also added the help wanted tag in case somebody will have time to fix it before I do.