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istanbuljs / babel-plugin-istanbul

A babel plugin that adds istanbul instrumentation to ES6 code
BSD 3-Clause "New" or "Revised" License
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"Container is falsy" error with recent versions of babel plugins and reassignment of loop-scoped variable #289

Closed jedwards1211 closed 1 day ago

jedwards1211 commented 3 months ago

I can't say for sure if the fault lies with the babel core packages or babel-plugin-istanbul...@babel/preset-env with forceAllTransforms: true by itself doesn't choke on the code below, and neither does babel-plugin-istanbul by itself. But when they're run together, an error gets thrown.

Issue repository

https://github.com/jedwards1211/babel-plugin-istanbul-issue

Code

for (let f; ; ) {
  f = "0";
  () => (0 ? 1 : parseInt(f));
}

The parseInt(f) gets transformed into cov_1c743zp148().b[0][1]++, parseInt(f). But for some reason that expression is orphaned by the time @babel/plugin-transform-block-scoping tries to rename f to _f, causing an error to be thrown.

Babel config

{
  "presets": [["@babel/preset-env", { "forceAllTransforms": true }]],
  "plugins": ["babel-plugin-istanbul"]
}

Package versions

    "@babel/cli": "^7.23.9",
    "@babel/preset-env": "^7.24.0",
    "babel-plugin-istanbul": "^6.1.1"

Error message

$ npm test

> babel-plugin-istanbul-issue@1.0.0 test
> babel index.js

ReferenceError: /Users/andy/gh/babel-plugin-istanbul-issue/index.js: Container is falsy
    at NodePath._replaceWith (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/traverse/lib/path/replacement.js:135:11)
    at NodePath.replaceWith (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/traverse/lib/path/replacement.js:126:8)
    at wrapLoopBody (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/plugin-transform-block-scoping/lib/loop.js:162:43)
    at PluginPass.Loop (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/plugin-transform-block-scoping/lib/index.js:82:50)
    at newFn (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/traverse/lib/visitors.js:160:14)
    at NodePath._call (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/traverse/lib/path/context.js:46:20)
    at NodePath.call (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/traverse/lib/path/context.js:36:17)
    at NodePath.visit (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/traverse/lib/path/context.js:82:31)
    at TraversalContext.visitQueue (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/traverse/lib/context.js:89:16)
    at TraversalContext.visitMultiple (/Users/andy/gh/babel-plugin-istanbul-issue/node_modules/@babel/traverse/lib/context.js:61:17) {
  code: 'BABEL_TRANSFORM_ERROR'
}