invalid block directive in minify-dead-code-elimination

[postspectacular]

Just encountered this error (w/ babel-plugin-minify-dead-code-elimination@0.1.7):

TypeError: bundle.js: block.get(...).filter is not a function
    at getUseStrictDirectives (.../node_modules/babel-plugin-minify-dead-code-elimination/lib/remove-use-strict.js:50:34)
    at removeUseStrict (.../node_modules/babel-plugin-minify-dead-code-elimination/lib/remove-use-strict.js:21:20)
    at PluginPass.exit (.../node_modules/babel-plugin-minify-dead-code-elimination/lib/index.js:844:13)
    at newFn (.../node_modules/babel-traverse/lib/visitors.js:276:21)
    at NodePath._call (.../node_modules/babel-traverse/lib/path/context.js:76:18)
    at NodePath.call (.../node_modules/babel-traverse/lib/path/context.js:48:17)
    at NodePath.visit (.../node_modules/babel-traverse/lib/path/context.js:117:8)
    at TraversalContext.visitQueue (.../node_modules/babel-traverse/lib/context.js:150:16)
    at TraversalContext.visitSingle (.../node_modules/babel-traverse/lib/context.js:108:19)
    at TraversalContext.visit (.../node_modules/babel-traverse/lib/context.js:192:19)
    at Function.traverse.node (.../node_modules/babel-traverse/lib/index.js:114:17)

I've added some debug traces and it seems that block.get("directives") doesn't always return an array, but sometimes an object too, in which case this error is triggered. Not sure about the internals of blocks, but maybe that's an upstream issue?

As a quick fix this works:

function getUseStrictDirectives(block) {
    var dir = block.get("directives");
    return dir.filter ? dir.filter(function (directive) {
        return directive.node.value.value === useStrict;
    }) : [];
}

[vigneshshanmugam]

Just wondering about the corner case, Can you give the test code where it got failed?

[boopathi]

Looks like a bug. Would you like to send a PR?

[postspectacular]

@vigneshshanmugam not easily, code base is >40k LOC and couldn't yet determine which part triggers it. I've noticed though that the block in question has an empty body, so guess this is caused by a previous optimization step (path.remove())...

{ type: 'BlockStatement',
  body: [],
  trailingComments: [],
  leadingComments: [],
  innerComments: [] }

So proposing a better fix based on that finding:

function getUseStrictDirectives(block) {
    return block.body && block.body.length ?
        block.get("directives").filter(function (directive) {
            return directive.node.value.value === useStrict;
        }) : [];
}

@boopathi sure, should this be based on master?

[vigneshshanmugam]

@postspectacular Thanks for explaining. Yes based on master.

[postspectacular]

@vigneshshanmugam no prob, still i think the real issue is somewhere else (in babel?) which causes block.get("directives") to return wrong data (NodePath instead of array) - this current fix is just addressing symptoms, not a cure...

[IgnusG]

I'm still getting this error. Running babel-preset-babili 0.1.4 with babel-cli 6.24.1 on node 8.1.3