fix options.sourceFileName gennerate bug

[creeperyang]

One corner usage:

sourceRoot: '/Users/me/work/SugarDev',
filename: '/private/tmp/wow/app.js'

// with previous path.relative
sourceFileName: '../../../../private/tmp/wow/app.js'

It seems just okay, but when webpack use webpack.optimize.UglifyJsPlugin with sourceMap, compilation will run into error. Because webpack.optimize.UglifyJsPlugin will try to access source map via '/private/tmp/wow/app.js'.

More info see webpack/webpack#2616

So we should fix the relative.

webpack use source-map handle source map, and source-map use its own relative: https://github.com/mozilla/source-map/blob/master/lib/util.js#L188-L226

Here I just replace path.relative with source-map's util.relative, and It will fix this error.

[joshwiens]

@creeperyang -

1.) Can you get this rebased and up to date so we can get it reviewed and landed?
2.) Add a test to cover the new relative function.

[creeperyang]

@d3viant0ne okay, I will do it.

[codecov-io]

Current coverage is 81.69% (diff: 100%)

Merging #260 into master will increase coverage by 1.69%

@@             master       #260   diff @@
==========================================
  Files             5          6     +1   
  Lines           140        153    +13   
  Methods          21         22     +1   
  Messages          0          0          
  Branches         30         33     +3   
==========================================
+ Hits            112        125    +13   
  Misses           13         13          
  Partials         15         15          

Powered by Codecov. Last update a8b9189...ea82899

[shankie-codes]

Any reason we can't get this merged? This is causing me some pretty serious issues at the moment!

Massive thanks to @creeperyang for sorting this! I would have never though of this...

[NickStefan]

@creeperyang I also would love to see this merged. Is this PR still alive?

[joshwiens]

@NickStefan - I'll give him a another day to respond and if we don't hear anything, i'll get in in directly.

[creeperyang]

Yeah, still alive. (conflicts resolved).

[danez]

Merged in 501d60d

[danez]

@creeperyang I kind of reverted this change and fixed it in a different way. This PR broke some cases on windows. #334 #339
I reproduced your initial problem with v6.2.7, and still cannot reproduce it with v6.2.9. If you have problems again, please open a ticket with a reproducible case, but let's hope this is fixed forever now 😇