💻

• Would you like to work on a fix?

How are you using Babel?

Programmatic API (babel.transform, babel.parse)

Input code

const b = require('@babel/core');
const t = require('@babel/template');

const template = t.smart(`function foo(%%arg%%: string) : void { }`, {
  plugins: ['typescript'],
  syntacticPlaceholders: true,
});

const stmt = template({
  arg: b.types.identifier('bar'),
});

console.log(stmt.params[0]);

Configuration file name

No response

Configuration

No response

Current and expected behavior

The string type annotation on the function parameter should still exist in the returned AST, but it does not. The output parameter AST from the code above is just this:

{ type: 'Identifier', name: 'bar' }

Doing the same thing using a non-syntactic placeholder returns this more complete parameter instead, which is expected:

{
  type: 'Identifier',
  name: 'bar',
  typeAnnotation: {
    type: 'TSTypeAnnotation',
    typeAnnotation: { type: 'TSStringKeyword', loc: undefined },
    loc: undefined
  }
}

Environment

System:

• OS: Linux 5.15 Ubuntu 22.04.4 LTS 22.04.4 LTS (Jammy Jellyfish) [Windows 11 + WSL2]

Binaries:

• Node: 20.13.0 - ~/.nvm/versions/node/v20.13.0/bin/node
• npm: 10.8.1 - ~/.nvm/versions/node/v20.13.0/bin/npm

npmPackages:

• @babel/core: ^7.25.2 => 7.25.2
• @babel/generator: ^7.25.6 => 7.25.6
• @babel/parser: ^7.25.6 => 7.25.6
• @babel/plugin-syntax-import-attributes: ^7.25.6 => 7.25.6
• @babel/plugin-syntax-typescript: ^7.25.4 => 7.25.4
• @babel/template: ^7.25.0 => 7.25.0
• @babel/traverse: ^7.25.6 => 7.25.6
• @babel/types: ^7.25.6 => 7.25.6
• babel-plugin-istanbul: ^7.0.0 => 7.0.0

Possible solution

No response

Additional context

I have patched my local copy of babel with the fix in #16903 to get past another issue (which worked). This behavior is consistent both with and without that patch.