Names missing from source map

[Nuru]

Bug Report

This happens with versions 7.2.0 (@babel/core 7.1.0) and 6.26.0 (babel-core 6.26.3). Version 7.2.0 example documented below.

Current Behavior
When minifying code, the generated source map has an empty names property, so dev tools are unable to unmangle variable names.

Input Code

var click = (base) => {
    let xtreme = 1;
    if (base)
      xtreme = xtreme + base;
    console.log(xtreme);
  }

Output Source

var click=a=>{let b=1;a&&(b+=a),console.log(b)};

Output Source Map

{"version":3,"sources":["foo.js"],"names":[],"mappings":"AAAA,GAAI,CAAA,KAAK,CAAI,CAAD,EAAU,CAClB,GAAI,CAAA,CAAM,CAAG,CAAb,CACI,CAFc,GAGhB,CAHgB,EAGE,CAHF,EAIlB,OAAO,CAAC,GAAR,CAAY,CAAZ,CACD,CALH","file":"foo.min.js","sourcesContent":["var click = (base) => {\n    let xtreme = 1;\n    if (base)\n      xtreme = xtreme + base;\n    console.log(xtreme);\n  }\n"]}

Expected behavior/code
Names base and extreme should be in the source map names array and properly mapped from a and b in the mapping.

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

% npx babel --presets=minify --source-type=script dev/foo.js --out-file=dev/foo.min.js --source-maps --no-babelrc 

Environment

• Babel version(s): 7.2.0 (@babel/core 7.1.0), 6.26.0 (babel-core 6.26.3
• Node/npm version: Node 8/npm 6
• OS: OSX 10.11.6
• Monorepo: no
• How you are using Babel: cli

Comments
Hard to call this a reversion of #27, but this should have been fixed with #3658.

[babel-bot]

Hey @Nuru! We really appreciate you taking the time to report an issue. The collaborators
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so it's possible this won't be addressed swiftly.

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[JennieJi]

Wow this still happens in latest version. Got test case here. And only fails in babel-cli, babel-core's transform works well. Not sure why babel-cli is not using same implementation from babel-core.