path.remove sometimes throws

[kangax]

We should probably address this in Babel, but I'm occasionally running into cases of path.remove() throwing error about context:

Here's an example from trying to run Nuclide codebase through Babili:

➜  Nuclide ./scripts/dev/release_transpile.js
7 workers. 1863 files...
Error transpiling "/Users/kangax/fbsource/fbobjc/Tools/Nuclide/pkg/fb-biggrep-cli/lib/biggrep.js"
/Users/kangax/fbsource/fbobjc/Tools/Nuclide/pkg/nuclide-node-transpiler/lib/NodeTranspiler.js:203
      throw err;
      ^

TypeError: unknown: Property consequent of ConditionalExpression expected node to be of a type ["Expression"] but instead got null
    at Object.validate (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-types/lib/definitions/index.js:109:13)
    at Object.validate (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-types/lib/index.js:511:9)
    at NodePath._replaceWith (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-traverse/lib/path/replacement.js:176:7)
    at NodePath._remove (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-traverse/lib/path/removal.js:58:10)
    at NodePath.remove (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-traverse/lib/path/removal.js:30:8)
    at PluginPass.CallExpression (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-plugin-transform-remove-console/lib/index.js:10:16)
    at newFn (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-traverse/lib/visitors.js:276:21)
    at NodePath._call (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-traverse/lib/path/context.js:76:18)
    at NodePath.call (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-traverse/lib/path/context.js:48:17)
    at NodePath.visit (/Users/kangax/fbsource/fbobjc/Tools/Nuclide/node_modules/babel-traverse/lib/path/context.js:105:12)

I narrowed it down to a combination of simplify and remove-console plugins, but there might be something else. The source code doesn't have anything unusual; just few expressions with console.log and console.error.

Temporary solution could be to wrap path.remove() in try/catch. Ideal one would be to find out what's causing this and fix it in Babel.

[kangax]

The problem could be us transforming if (x) { console.log('...') } to if (x) { } and then trying to turn that to x && ... where the RHS doesn't exist? Or something along those lines.

[kangax]

facebook/react-native#10412 seems related (as brought up by @danez)

[boopathi]

Hmmm.. I tried reproducing that in babel.

http://astexplorer.net/#/G38YR5EEES

[danez]

It seems in a lot of cases console.log cannot just simply be removed but would rather need to be replaced by something.

In the example I replaced it with undefined.

http://astexplorer.net/#/G38YR5EEES/2

[boopathi]

@danez

Ah. That makes sense. When we remove, we have to know the context of where it is. But doesn't babel's path.remove already do this? It inserts an EmptyStatement or a BlockStatement when you remove node.consequent or alternate in a IfStatement.

[danez]

Maybe this is broken.

Interestingly if i do:

var t = () => console.log('1st');

it turns correctly into:

var t = () => void 0;