Improve source map support

[jhnns]

• Make all source map paths relative to the entry file. This way we don't have to read the context option from the webpack config.

• Fix source maps on Windows: node-sass returns POSIX paths, that's why we need to transform them back to native paths. This fixes an error on windows where the source-map module cannot resolve the source maps.

See #366 (comment)

[jhnns]

@bholloway this will again be breaking for the resolve-url-loader. I've created a PR for this: bholloway/resolve-url-loader#44

[bholloway]

@jhnns Can you confirm that module imports (i.e. tilde ~) are relative to the entry file? I am seeing otherwise.

I will try to reproduce with your /test project.

[bholloway]

@jhnns I have tweaked your bootstrapSass test to debug the source-maps.

The source code is in this gist. It requires you to install adjust-sourcemap-loader.

The overall output is of the form:

{
  "sources": [
    "webpack:///webpack:///test/scss/bootstrap-sass.scss",
    "webpack:///webpack:///test/scss/~/bootstrap-sass/assets/stylesheets/_bootstrap.scss"
    ...
  ]
  ...,
  "sourceRoot": ""
}

We can ignore the repeated webpack:/// protocol for now. It has been a while since I debugged source-maps but the tilde in the path certainly feels wrong.

I am less interested in the overall output and more interested in what goes into the resolve-url-loader.

The debug output from adjust-sourcemap-loader shows the source-map following sass-loader (i.e. at its input):

INPUT bootstrap-sass.scss
      node_modules/bootstrap-sass/assets/stylesheets/_bootstrap.scss
      node_modules/bootstrap-sass/assets/stylesheets/bootstrap/_variables.scss
      ...

While this debug info does not include the sourceRoot I believe a "sourceRoot": "test/scss" would produce the overall output we see above. However you can see there is no common source root possible for these paths.

(Please Note the adjust-sourcemap-loader will try to locate files using all the CODECs at its disposal. That is the ABSOLUTE path in the debug output. However that does not help us here.)

[jhnns]

These source maps are truly driving me crazy ^^

Could you review #377 and try it with your test setup? I think, now all paths should be correct.

[bholloway]

@jhnns There is good news and bad news. I will comment on #377 because it is still open.