export types.BaseNode for generic utility use

[kentcdodds]

Q	A
Fixed Issues?	N/A
Patch: Bug Fix?	N/A
Major: Breaking Change?	N/A
Minor: New Feature?	👍
Tests Added + Pass?	N/A
Documentation PR Link	N/A
Any Dependency Changes?	No
License	MIT

I'm trying to write a utility that accepts a NodePath of any BaseNode type and does stuff with it (replaces etc.). So I need to type that utility with BaseNode, but that's not exported yet so this simply exports the BaseNode.

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[nicolo-ribaudo]

Does NodePath<Node> work for you, as opposed to NodePath<BaseNode>?

[kentcdodds]

It didn't when I tried. I think it's because Node isn't in the inheritance chain or something 🤔

[nicolo-ribaudo]

Is that code public? I have nothing against exposing BaseNode if it's needed, but I am very surprised that Node does not work since it's the union of all the possible nodes.

[kentcdodds]

Yeah, mauve I did something wrong, but using Node here didn't work: https://github.com/kentcdodds/babel-plugin-codegen/blob/pr/migrate-to-ts/src/helpers.ts#L85

[nicolo-ribaudo]

Ok I see the error:

src/replace.ts:55:9 - error TS2322: Type 'NodePath<ImportDeclaration>' is not assignable to type 'NodePath<Node>'.
  Type 'Node' is not assignable to type 'ImportDeclaration'.

I tried to export BaseNode in node_modules/@babel/types and I still get

src/replace.ts:55:9 - error TS2322: Type 'NodePath<ImportDeclaration>' is not assignable to type 'NodePath<BaseNode>'.
  Type 'BaseNode' is missing the following properties from type 'ImportDeclaration': specifiers, source

I think it has to do with covariance/contravariance of type parameters (I don't know exactly what it means), but I fixed the type errors like this:

diff --git a/src/helpers.ts b/src/helpers.ts
index c813b8f..0701b03 100644
--- a/src/helpers.ts
+++ b/src/helpers.ts
@@ -63,9 +63,9 @@ function getReplacement(
   })()
 }
 
-function applyReplacementToPath(
+function applyReplacementToPath<SpecificNode extends babelCore.types.Node>(
   replacement: babelCore.Node | Array<babelCore.Node> | null | undefined,
-  path: babelCore.NodePath,
+  path: babelCore.NodePath<SpecificNode>,
 ) {
   if (replacement) {
     // If it's not an array, wrap into an array
@@ -79,16 +79,16 @@ function applyReplacementToPath(
   }
 }
 
-type ReplaceOptions = {
+type ReplaceOptions<SpecificNode extends babelCore.types.Node> = {
   // https://github.com/babel/babel/pull/12600
   // path: babelCore.NodePath<babelCore.types.BaseNode>
-  path: babelCore.NodePath<any>
+  path: babelCore.NodePath<SpecificNode>
   code: string | Buffer
   fileOpts: babelCore.TransformOptions
   args?: Array<any>
 }
-function replace(
-  {path, code, fileOpts, args}: ReplaceOptions,
+function replace<SpecificNode extends babelCore.types.Node>(
+  {path, code, fileOpts, args}: ReplaceOptions<SpecificNode>,
   babel: typeof babelCore,
 ) {
   const replacement = getReplacement({code, args, fileOpts}, babel)

[kentcdodds]

That worked. Thank you for taking the time @nicolo-ribaudo! Cheers :)