Using a decorator breaks the enumerability of non-decorated fields

[mweststrate]

v7 Regression

Potential Commit/PR that introduced the regression

Probably #7976, but didn't verify

Describe the regression

If @babel/plugin-proposal-class-properties is used to initialize a class field, the field becomes non-enumerable if there are decorators used in the same class. (Despite being applied to different fields)

• This happens only when legacy: false is used for @babel/plugin-proposal-decorators (it succeeds in legacy mode)
• This happens both when using loose and non-loose mode for proposal-class-properties
• This does not happen in Babel 6

Input Code
(Could not verify in Repl as it still uses babel 6)

    class Todo1 {
        id = 1
    }

    function dec(el) {
        return el
    }
    class Todo2 {
        id = 1;
        @dec x
    }

    const t1 = new Todo1()
    expect(Object.getOwnPropertyDescriptor(t1, "id").enumerable).toBe(true)

    const t2 = new Todo2()
    expect(Object.getOwnPropertyDescriptor(t2, "id").enumerable).toBe(true) // this test fails, just by introducing the unrelated `@dec x` field

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

{
    "presets": ["@babel/preset-env"],
    "plugins": [
        ["@babel/plugin-proposal-decorators", { "legacy": false, "decoratorsBeforeExport": true }],
        ["@babel/plugin-proposal-class-properties", { "loose": true }]
    ]
}

Expected behavior/code
A clear and concise description of what you expected to happen (or code).

Environment

• Babel version(s): [7.1.0]
• Node/npm version: [8.11.3]
• OS: [Ubuntu]
• Monorepo [no]
• How you are using Babel: [babel-jest]

[babel-bot]

Hey @mweststrate! 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.

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[mweststrate]

Thanks @nicolo-ribaudo!