xo returns "undefined" randomly

[niftylettuce]

When combined with vim-autoformat it will replace the contents of a file entirely with the string "undefined" as per https://github.com/Chiel92/vim-autoformat/issues/200.

I tried running it from the CLI and was able to reproduce the issue @sindresorhus.

cat app/controllers/admin/order.js | DEBUG=* xo --fix --stdin

Output (note the very last line says "undefined" for some reason)

  eslint-plugin-import:rules:newline-after-import node position in scope: 0 +104ms
  eslint-plugin-import:rules:newline-after-import node position in scope: 1 +0ms
  eslint-plugin-import:rules:newline-after-import node position in scope: 2 +0ms
  eslint-plugin-import:rules:newline-after-import node position in scope: 3 +0ms
  eslint-plugin-import:rules:newline-after-import node position in scope: 4 +0ms
  eslint-plugin-import:rules:newline-after-import node position in scope: 5 +0ms
  eslint-plugin-import:rules:newline-after-import node position in scope: 6 +0ms
  eslint-plugin-import:rules:newline-after-import node position in scope: 7 +0ms
  eslint:code-path onCodePathSegmentEnd s1_1 +135ms
  eslint:code-path onCodePathEnd s1 +0ms
  eslint:code-path DOT
digraph {
node[shape=box,style="rounded,filled",fillcolor=white];
initial[label="",shape=circle,style=filled,fillcolor=black,width=0.25,height=0.25];
final[label="",shape=doublecircle,style=filled,fillcolor=black,width=0.25,height=0.25];
s1_1[label="Program\nVariableDeclaration\nVariableDeclarator\nIdentifier (lodash)\nCallExpression\nIdentifier (require)\nLiteral (lodash)\nVariableDeclaration\nVariableDeclarator\nIdentifier (querystring)\nCallExpression\nIdentifier (require)\nLiteral (querystring)\nVariableDeclaration\nVariableDeclarator\nIdentifier (util)\nCallExpression\nIdentifier (require)\nLiteral (util)\nVariableDeclaration\nVariableDeclarator\nIdentifier (async)\nCallExpression\nIdentifier (require)\nLiteral (async)\nVariableDeclaration\nVariableDeclarator\nIdentifier (_)\nCallExpression\nIdentifier (require)\nLiteral (underscore)\nVariableDeclaration\nVariableDeclarator\nIdentifier (moment)\nCallExpression\nIdentifier (require)\nLiteral (moment)\nVariableDeclaration\nVariableDeclarator\nIdentifier (accounting)\nCallExpression\nIdentifier (require)\nLiteral (accounting)\nVariableDeclaration\nVariableDeclarator\nIdentifier (s)\nCallExpression\nIdentifier (require)\nLiteral (underscore.string)\nVariableDeclaration\nVariableDeclarator\nIdentifier (lib)\nExpressionStatement\nAssignmentExpression\nMemberExpression\nIdentifier (module)\nIdentifier (exports)\nFunctionExpression\nFunctionDeclaration\nVariableDeclaration\nVariableDeclarator\nIdentifier (mergeOrders)\nObjectExpression\nProperty\nIdentifier (retrieve)\nArrowFunctionExpression\nProperty\nIdentifier (create)\nArrowFunctionExpression\nVariableDeclaration\nVariableDeclarator\nIdentifier (changeMarketDay)\nObjectExpression\nProperty\nIdentifier (retrieve)\nArrowFunctionExpression\nProperty\nIdentifier (update)\nArrowFunctionExpression\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nFunctionDeclaration\nIdentifier:exit (lodash)\nIdentifier:exit (require)\nLiteral:exit (lodash)\nCallExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (querystring)\nIdentifier:exit (require)\nLiteral:exit (querystring)\nCallExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (util)\nIdentifier:exit (require)\nLiteral:exit (util)\nCallExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (async)\nIdentifier:exit (require)\nLiteral:exit (async)\nCallExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (_)\nIdentifier:exit (require)\nLiteral:exit (underscore)\nCallExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (moment)\nIdentifier:exit (require)\nLiteral:exit (moment)\nCallExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (accounting)\nIdentifier:exit (require)\nLiteral:exit (accounting)\nCallExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (s)\nIdentifier:exit (require)\nLiteral:exit (underscore.string)\nCallExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (lib)\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (module)\nIdentifier:exit (exports)\nMemberExpression:exit\nFunctionExpression:exit\nAssignmentExpression:exit\nExpressionStatement:exit\nFunctionDeclaration:exit\nIdentifier:exit (mergeOrders)\nIdentifier:exit (retrieve)\nArrowFunctionExpression:exit\nProperty:exit\nIdentifier:exit (create)\nArrowFunctionExpression:exit\nProperty:exit\nObjectExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nIdentifier:exit (changeMarketDay)\nIdentifier:exit (retrieve)\nArrowFunctionExpression:exit\nProperty:exit\nIdentifier:exit (update)\nArrowFunctionExpression:exit\nProperty:exit\nObjectExpression:exit\nVariableDeclarator:exit\nVariableDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nFunctionDeclaration:exit\nProgram:exit"];
initial->s1_1->final;
} +0ms
  eslint:cli-engine Generating fixed text for <text> (pass 1) +1ms
  eslint:text-fixer Applying fixes +1ms
  eslint:text-fixer No fixes to apply +0ms
undefined

[niftylettuce]

Note that if I run this without the stdin flag it works perfectly fine.

[niftylettuce]

cat app/controllers/admin/order.js | DEBUG=* xo --stdin works as well (without --fix flag)

[niftylettuce]

@sindresorhus It looks like here we are looking for a results[0].output (String) property, but sometimes it's empty or undefined? I did a console.log of results[0].output and it was undefined, but results[0].source was there and such.

https://github.com/sindresorhus/xo/blob/2e4071c552f91de654ea099885c4eeec9607691a/main.js#L100

[niftylettuce]

@sindresorhus I've narrowed down the problem to eslint CLI engine, pinging @nzakas to help here possibly.

Obviously the issue is that the conditional never is reached:

https://github.com/eslint/eslint/blob/master/lib/cli-engine.js#L221-L223

[niftylettuce]

I've fixed this issue per https://github.com/Chiel92/vim-autoformat/pull/205