Intermittent compilation error when using LESS loader

[seaBubble]

🐞 Bug report

Command (mark with an x)

- [ ] new
- [ ] build
- [x] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

Is this a regression?

No

Description

In an Angular project using LESS, if I serve the app, sometimes an error is thrown while compiling the LESS code. If I run ng serve again, sometimes it goes away, sometimes I need to serve it again.

🔬 Minimal Reproduction

ng serve
throws, sometimes only,
an error described below
always pointing at the same LESS file, which contains

@types: ~'type1' ~'type2';
.for(@i, @n) {
  .-each(@i);
}
.for(@n) when (isnumber(@n)) {
  .for(1, @n);
}

.for(@i, @n) when not (@i = @n) {
  .for((@i + (@n - @i) / abs(@n - @i)), @n);
}

.for(@array) when (default()) {
  .for-impl_(length(@array));
}

.for-impl_(@i) when (@i > 1) {
  .for-impl_((@i - 1));
}

.for-impl_(@i) {
  .-each(extract(@array, @i));
}
.mixin-test() {
  .for(@types);
  .-each(@name) {
    .define(@name);
    .status-icon-@{name}& {
      color: @@color;
    }
  }
}


.mixin-test(); 

🔥 Exception or Error

Module build failed (from ./node_modules/less-loader/dist/cjs.js):

 


Cannot read property 'substring' of undefined

      in undefined (line undefined, column undefined)

TypeError: Cannot read property 'substring' of undefined

    at SourceMapOutput.add /node_modules/less/lib/less/source-map-output.js:72:39)

    at Element.genCSS (/node_modules/less/lib/less/tree/element.js:46:12)

    at Selector.genCSS (/node_modules/less/lib/less/tree/selector.js:125:17)

    at Ruleset.genCSS (/node_modules/less/lib/less/tree/ruleset.js:484:21)

    at Ruleset.genCSS (/node_modules/less/lib/less/tree/ruleset.js:508:18)

    at SourceMapOutput.toCSS (/node_modules/less/lib/less/source-map-output.js:123:24)

    at SourceMapBuilder.toCSS (/node_modules/less/lib/less/source-map-builder.js:23:35)

    at ParseTree.toCSS (/node_modules/less/lib/less/parse-tree.js:33:47)

    at /node_modules/less/lib/less/render.js:35:40

    at /node_modules/less/lib/less/parse.js:86:21

    at ImportVisitor.finish [as _finish] (/node_modules/less/lib/less/parser/parser.js:240:28)

    at ImportVisitor._onSequencerEmpty (/node_modules/less/lib/less/visitors/import-visitor.js:36:14)

    at ImportSequencer.tryRun (/node_modules/less/lib/less/visitors/import-sequencer.js:50:14)

    at /node_modules/less/lib/less/visitors/import-sequencer.js:19:25

    at fileParsedFunc (/node_modules/less/lib/less/import-manager.js:63:17)

    at loadFileCallback (/node_modules/less/lib/less/import-manager.js:133:21)

    at process._tickCallback (internal/process/next_tick.js:68:7)

 @ ./src/app/test.component.ts 44:21-65

 @ ./src/app/test.module.ts

@ ./src/app/app.module.ts

 @ ./src/main.ts

 @ multi (webpack)-dev-server/client?http://0.0.0.0:0/sockjs-node ./src/main.ts

 

ERROR in ./src/app/test.component.less

Module build failed (from ./node_modules/less-loader/dist/cjs.js):

 

 

Cannot read property 'substring' of undefined

      in undefined (line undefined, column undefined)

TypeError: Cannot read property 'substring' of undefined

    at SourceMapOutput.add (/node_modules/less/lib/less/source-map-output.js:72:39)

    at Element.genCSS (/node_modules/less/lib/less/tree/element.js:46:12)

    at Selector.genCSS (/node_modules/less/lib/less/tree/selector.js:125:17)

    at Ruleset.genCSS (/node_modules/less/lib/less/tree/ruleset.js:484:21)

    at Ruleset.genCSS (/node_modules/less/lib/less/tree/ruleset.js:508:18)

    at SourceMapOutput.toCSS (/node_modules/less/lib/less/source-map-output.js:123:24)

    at SourceMapBuilder.toCSS (/node_modules/less/lib/less/source-map-builder.js:23:35)

    at ParseTree.toCSS (/node_modules/less/lib/less/parse-tree.js:33:47)

    at /node_modules/less/lib/less/render.js:35:40

    at /node_modules/less/lib/less/parse.js:86:21

    at ImportVisitor.finish [as _finish] (/node_modules/less/lib/less/parser/parser.js:240:28)

    at ImportVisitor._onSequencerEmpty (/node_modules/less/lib/less/visitors/import-visitor.js:36:14)

    at ImportSequencer.tryRun (/node_modules/less/lib/less/visitors/import-sequencer.js:50:14)

    at /node_modules/less/lib/less/visitors/import-sequencer.js:19:25

    at fileParsedFunc (/node_modules/less/lib/less/import-manager.js:63:17)

    at loadFileCallback (/node_modules/less/lib/less/import-manager.js:133:21)

    at process._tickCallback (internal/process/next_tick.js:68:7)

 @ ./src/app/test.component.ts 44:21-65

 @ ./src/app/test.module.ts

 @ ./src/app/app.module.ts

 @ ./src/main.ts

 @ multi (webpack)-dev-server/client?http://0.0.0.0:0/sockjs-node ./src/main.ts

ℹ ｢wdm｣: Failed to compile.

🌍 Your Environment

Angular CLI: 7.3.8
Node: 10.5.0
OS: darwin x64
Angular: 7.2.14
... animations, common, compiler, core, forms, http
... platform-browser, platform-browser-dynamic, router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.13.8
@angular-devkit/build-angular     0.13.8
@angular-devkit/build-optimizer   0.13.8
@angular-devkit/build-webpack     0.13.8
@angular-devkit/core              7.3.8
@angular-devkit/schematics        7.3.8
@angular/cdk                      7.3.7
@angular/cli                      7.3.8
@angular/compiler-cli             7.2.3
@angular/language-service         7.2.3
@angular/material                 7.3.7
@ngtools/webpack                  7.3.8
@schematics/angular               7.3.8
@schematics/update                0.13.8
rxjs                              6.5.2
typescript                        3.2.4
webpack                           4.29.0

[alan-agius4]

This seems like a bug but we'll need to look at a reproduction to find and fix the problem. Can you setup a minimal repro please?

You can read here why this is needed. A good way to make a minimal repro is to create a new app via ng new repro-app and adding the minimum possible code to show the problem. Then you can push this repository to github and link it here.

This might be related to your directory structure so its really important to get an accurate repro to diagnose this.

[alan-agius4]

Thanks for reporting this issue. However, you didn't provide sufficient information for us to understand and reproduce the problem. Please check out our submission guidelines to understand why we can't act on issues that are lacking important information.

If the problem persists, please file a new issue and ensure you provide all of the required information when filling out the issue template.

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