Check for tokens length before accessing

[ramya-rao-a]

The css parser fails to parse the below less example from http://lesscss.org/features/#loops-feature

.generate-columns(4);

.generate-columns(@n, @i: 1) when (@i =< @n) {
  .column-@{i} {
    width: (@i * 100% / @n);
  }
  .generate-columns(@n, (@i + 1));
}

This PR will fix the parsing issue

cc @sergeche

[sergeche]

Have to check it more thoroughly, I’m developing a new Emmet feature for LESS and SCSS based on CSS parser, might be already solved

[ramya-rao-a]

The current fix is pretty harmless. It ensures that tokens array is not empty before trying to access tokens[0]

[rzhao271]

Have to check it more thoroughly, I’m developing a new Emmet feature for LESS and SCSS based on CSS parser, might be already solved

@sergeche any updates on this repo for LESS and SCSS, or is the new feature within the main Emmet repo?

[sergeche]

Is this issue reproducible in new Emmet?

[rzhao271]

Sorry, didn't realize that new changes were added to this repo since v0.4.0 😅
I have been working on other parts of vscode and haven't tried reproducing this issue yet, though.

[rzhao271]

Alright, just tested it with v0.4.0.
I created a new LESS file with the same contents as #1 (comment).

Then, I tried expanding an abbreviation, which causes the parser to run, and I see the following error:

TypeError: Cannot read property 'type' of undefined
        at parseStylesheet (/home/node/workspace/vscode/extensions/emmet/node_modules/@emmetio/css-parser/dist/css-parser.cjs.js:1490:22)
        at Object.getRootNode (/home/node/workspace/vscode/extensions/emmet/out/parseDocument.js:24:26)
        at getRootNode (/home/node/workspace/vscode/extensions/emmet/out/abbreviationActions.js:324:40)
        at /home/node/workspace/vscode/extensions/emmet/out/abbreviationActions.js:338:46
        at Array.forEach (<anonymous>)
        at Obj…/ipc/common/ipc.net.js:189:37)
        at /home/node/workspace/vscode/out/vs/base/parts/ipc/common/ipc.net.js:158:61
        at Socket.listener (/home/node/workspace/vscode/out/vs/base/parts/ipc/node/ipc.net.js:17:40)
        at Socket.emit (events.js:315:20)
        at addChunk (_stream_readable.js:295:12)
        at readableAddChunk (_stream_readable.js:271:9)
        at Socket.push (_stream_readable.js:212:10)
        at Pipe.onStreamRead (internal/stream_base_commons.js:186:23)
        at Pipe.callbackTrampoline (internal/async_hooks.js:120:14)

I also confirmed that this error does not show up with Ramya's patch.