generate higher quality SourceMaps #109
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## master #109 +/- ##
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Coverage 98.58% 98.58%
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Files 5 5
Lines 283 283
Branches 113 113
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Hits 279 279
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sokra
commented
Jul 31, 2019
| @@ -55,7 +55,7 @@ Object { | |||
| "code": "function foo(f){if(f)return bar()}", | |||
| "error": undefined, | |||
| "extractedComments": Array [], | |||
| "map": "{\\"version\\":3,\\"sources\\":[\\"test1.js\\"],\\"names\\":[\\"foo\\",\\"x\\",\\"not_called1\\"],\\"mappings\\":\\"AAAA,SAASA,IAAIC,GACT,GACIA,EAAA,OACAC\\"}", | |||
| "map": "{\\"version\\":3,\\"sources\\":[\\"test6.js\\"],\\"names\\":[\\"foo\\",\\"x\\",\\"bar\\"],\\"mappings\\":\\"AAAA,SAASA,IAAIC,GAAK,GAAIA,EAAK,OAAOC\\"}", | |||
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We no longer apply the inputSourceMap in the worker, so this snapshot has changed.
It was incorrect anyway since not_called1 should not be in the SourceMap as it is dropped by terser.
sokra
commented
Jul 31, 2019
| Error: \\"version\\" is a required argument.", | ||
| ] | ||
| `; | ||
| exports[`when options.sourceMap matches snapshot for a single \`true\` value (\`devtool\` is \`source-map\`) and source map invalid: errors 1`] = `Array []`; |
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This no longer crashes, but a warning is still displayed.
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This PR contains a:
Motivation / Use-Case
fixes webpack/webpack#8302
Mappings generated when combining bundle source map with terser source map are not very fine, which leads to validation errors and low quality source maps.
There are many causes:
We had a similar problem with webpack replacements (using the
ReplaceSourcefrom webpack-sources) and a good fix turned out to be:Assume that mappings, where generates source and original source are identical for a mapping, map source code char by char.
With this assumption mappings don't have to be super exact as long code stays equal. This allows to apply the high quality terser SourceMap to the lower quality webpack SourceMap without loosing quality.
webpack-sources now implements with kind of assumption (I call it "identity" mappings) for
SourceMapSource. This PR changes terser-webpack-plugin to use it.Test snapshots are updated with new mappings that include more column information.
Breaking Changes
This should have no breaking changes. SourceMaps are very similar, but with additional column information.
Additional Info
For reviewing see only second commit. First commit changes snapshot format to be easier reviewable.