Type annotation is stripped from Typescript template

[dentrado]

Bug Report

Current Behavior
A @babel/template template with placeholders and a type annotation generates code without the annotation. A template without placeholders works as expected.

Input Code

const template = require('@babel/template').default
const generate = require('@babel/generator').default
const t = require('@babel/types')
​
const withType = template({plugins:['typescript']}).ast`
    const greeting: string = 'Hello';
`
console.log(generate(withType).code)
// => "const greeting: string = 'Hello';"
​
const typeDisappears = template({plugins:['typescript']}).ast`
    const ${t.identifier('greeting')}: string = 'Hello';
`
console.log(generate(typeDisappears).code)
// => "const greeting = 'Hello';"

Expected behavior/code

I expect both templates above to keep the : string type in the generated code.

Babel Configuration (.babelrc, package.json, cli command)

No configuration, used from code, see above.

Environment

• Babel version(s): 7.6.4
• Node/npm version: Node 12.9.1 / yarn 1.17.3
• Monorepo: no

[babel-bot]

Hey @dentrado! We really appreciate you taking the time to report an issue. The collaborators on this project attempt to help as many people as possible, but we're a limited number of volunteers, so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack community that typically always has someone willing to help. You can sign-up here for an invite."

[nicolo-ribaudo]

The root cause of this bug is that the type annotation is a child node of the identifier. The identifier you are passing to @babel/template doesn't have the type annotation, and thus the one in the template is discarded.

#9545 would be a possible way of fixing this.