babel-plugin-flow-runtime references undefined type parameter names with assertions disabled #180

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This is a:

• Bug Report
• Feature Request
• Question
• Other

Which concerns:

• flow-runtime
• babel-plugin-flow-runtime
• flow-runtime-validators
• flow-runtime-mobx
• flow-config-parser
• The documentation website

---

Code

// @flow

function foo<X>() {
  let bar: X
}

.babelrc

{
  "presets": ["es2015"],
  "plugins": [
    "transform-decorators-legacy",
    ["flow-runtime", {"assert": false}]
  ]
}

What is the current behaviour?

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---

X is undefined in the output code below at let _barType = X:

import t from "flow-runtime";
function foo() {
  let _barType = X,
      bar;
}
t.annotate(foo, t.function(_fn => {
  const X = _fn.typeParameter("X");

  return [];
}));

What is the expected behaviour?

<!-- Please describe what you'd expect to happen under these circumstances. If you are describing a bug in the babel plugin, please indicate the output you'd expect it to produce. -->

---

Either babel-plugin-flow-runtime doesn't create _barType, or it inserts const X = t.typeParameter("X") above let _barType it despite the "assert": false in the plugin options.

Which package versions are you using?

<!-- If this is a bug, which version(s) of the affected package(s) are you using? If you're describing a bug specific to an environment, like a certain browser or node version, please include that information here too. -->

├── babel-core@6.26.0 
├── babel-plugin-flow-runtime@0.15.0 
├── babel-preset-es2015@6.24.0