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Metro may produce invalid source maps with Terser minification enabled. #927

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robhogan opened this issue Feb 16, 2023 · 0 comments
Closed

Metro may produce invalid source maps with Terser minification enabled. #927

robhogan opened this issue Feb 16, 2023 · 0 comments

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@robhogan
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robhogan commented Feb 16, 2023 •
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This was originally reported against react-native-bundle-visualizer by @frankcalise in IjzerenHein/react-native-bundle-visualizer#116 (CC @frankcalise, @hurali97).

What is the current behavior?
When using metro-minify-terser (as is now default), Metro may produce source maps that contain invalid entries. This prevents source-map-explorer from working at all, and is likely to affect other tools.

If the current behavior is a bug, please provide the steps to reproduce and a minimal repository on GitHub that we can yarn install and yarn test.

git clone https://github.com/frankcalise/react-native-vanilla-reanimated
yarn
yarn run visualizer

(Pin react-native-bundle-visualizer to 3.1.2 to reproduce before the workaround (IjzerenHein/react-native-bundle-visualizer@af0289c) was released)

Or

yarn add source-map-explorer
yarn run react-native bundle --platform=ios --dev=false --entry-file=./index.js --bundle-output=terser.bundle --sourcemap-output terser.bundle.map --minify --reset-cache
yarn run source-map-explorer terser.bundle terser.bundle.map

What is the expected behavior?
A source-map derived visualisation of dependencies.

Metro 0.75.0
@robhogan robhogan mentioned this issue Feb 16, 2023
Closed
robhogan added a commit to robhogan/metro that referenced this issue Feb 16, 2023
@robhogan @facebook-github-bot
Handle "simple" (missing origin) source mappings in minifier output
66914bf 
Summary:
Fixes facebook#927

Terser, unlike the previous default minifier UglifyES, produces source maps whose entries may contain "simple mappings" - that is entries with a generated line+col but no original location.

When Metro merges source maps to serialize minified output, it doesn't correctly handle these entries. Instead it incorrectly detects them as complete mappings and produces a merged source map with `-1` origin line numbers in place of simple mappings.

Some tools will reject the whole source map (which is otherwise correct) based on the appearance of a negative line number.

The issue comes down to the conversion of raw mappings to `BabelSourceMapSegments` in `toBabelSegments`, which currently generates entries for simple mappings with `null` `origin` *properties*, such as:

```
{
  generated: {
    column: 2,
    line: 1
  },
  origin: {
    column: null,
    line: null
  },
  // ...
}
```

According to the Flow type for `BabelSourceMapSegments`, that's incorrect. `origin` itself is optional and should be missing - the properties of `origin` are not nullable.

Based on the presence of the `origin` property in that object, `toSegmentTuple` generates a 4-tuple and we go on to add a "source mapping" rather than a "simple mapping".

This fixes `toBabelSegments` to omit `origin` unless `line` and `column` are both populated. The final source map output is then correct.

Differential Revision: D43351987

fbshipit-source-id: 5ba5e9edc6913d1feaf7a6b1827ad43e579fbada
robhogan added a commit to robhogan/metro that referenced this issue Feb 16, 2023
@robhogan @facebook-github-bot
Handle "simple" (missing origin) source mappings in minifier output (f…
ed4a813 
…acebook#928)

Summary:
Pull Request resolved: facebook#928

Fixes facebook#927

Terser, unlike the previous default minifier UglifyES, produces source maps whose entries may contain "simple mappings" - that is entries with a generated line+col but no original location.

When Metro processes minified output ahead of serialization, it doesn't correctly handle these entries. Instead it incorrectly detects them as complete mappings and produces a merged source map with `-1` origin line numbers in place of simple mappings.

Some tools will reject the whole source map (which is otherwise correct) based on the appearance of a negative line number.

The issue comes down to the conversion of raw mappings to `BabelSourceMapSegments` in `toBabelSegments`, which currently generates entries for simple mappings with `null` `origin` *properties*, such as:

```
{
  generated: {
    column: 2,
    line: 1
  },
  origin: {
    column: null,
    line: null
  },
  // ...
}
```

According to the Flow type for `BabelSourceMapSegments`, that's incorrect. `origin` itself is optional and should be missing - the properties of `origin` are not nullable.

Based on the presence of the `origin` property in that object, `toSegmentTuple` generates a 4-tuple and we go on to add a "source mapping" rather than a "simple mapping".

This fixes `toBabelSegments` to omit `origin` unless `line` and `column` are both populated. The final source map output is then correct.

Changelog: [Fix] Source maps may have invalid entries when using Terser minification.

Reviewed By: motiz88

Differential Revision: D43351987

fbshipit-source-id: 706cf2e90cb33ebc8223b449b2c280156512c9a4
robhogan added a commit that referenced this issue Feb 18, 2023
@robhogan
Handle "simple" (missing origin) source mappings in minifier output (#…
9c0229b 
…928)

Summary:
Pull Request resolved: #928

Fixes #927

Terser, unlike the previous default minifier UglifyES, produces source maps whose entries may contain "simple mappings" - that is entries with a generated line+col but no original location.

When Metro processes minified output ahead of serialization, it doesn't correctly handle these entries. Instead it incorrectly detects them as complete mappings and produces a merged source map with `-1` origin line numbers in place of simple mappings.

Some tools will reject the whole source map (which is otherwise correct) based on the appearance of a negative line number.

The issue comes down to the conversion of raw mappings to `BabelSourceMapSegments` in `toBabelSegments`, which currently generates entries for simple mappings with `null` `origin` *properties*, such as:

```
{
  generated: {
    column: 2,
    line: 1
  },
  origin: {
    column: null,
    line: null
  },
  // ...
}
```

According to the Flow type for `BabelSourceMapSegments`, that's incorrect. `origin` itself is optional and should be missing - the properties of `origin` are not nullable.

Based on the presence of the `origin` property in that object, `toSegmentTuple` generates a 4-tuple and we go on to add a "source mapping" rather than a "simple mapping".

This fixes `toBabelSegments` to omit `origin` unless `line` and `column` are both populated. The final source map output is then correct.

Changelog: [Fix] Source maps may have invalid entries when using Terser minification.

Reviewed By: motiz88

Differential Revision: D43351987

fbshipit-source-id: 5cd46fdd001f3c3a3599ada44f525bec467854e1
@robhogan robhogan mentioned this issue Feb 18, 2023
Merged
robhogan added a commit that referenced this issue Feb 19, 2023
@robhogan
Handle "simple" (missing origin) source mappings in minifier output (#…
84947c7 
…928)

Summary:
Pull Request resolved: #928

Fixes #927

Terser, unlike the previous default minifier UglifyES, produces source maps whose entries may contain "simple mappings" - that is entries with a generated line+col but no original location.

When Metro processes minified output ahead of serialization, it doesn't correctly handle these entries. Instead it incorrectly detects them as complete mappings and produces a merged source map with `-1` origin line numbers in place of simple mappings.

Some tools will reject the whole source map (which is otherwise correct) based on the appearance of a negative line number.

The issue comes down to the conversion of raw mappings to `BabelSourceMapSegments` in `toBabelSegments`, which currently generates entries for simple mappings with `null` `origin` *properties*, such as:

```
{
  generated: {
    column: 2,
    line: 1
  },
  origin: {
    column: null,
    line: null
  },
  // ...
}
```

According to the Flow type for `BabelSourceMapSegments`, that's incorrect. `origin` itself is optional and should be missing - the properties of `origin` are not nullable.

Based on the presence of the `origin` property in that object, `toSegmentTuple` generates a 4-tuple and we go on to add a "source mapping" rather than a "simple mapping".

This fixes `toBabelSegments` to omit `origin` unless `line` and `column` are both populated. The final source map output is then correct.

Changelog: [Fix] Source maps may have invalid entries when using Terser minification.

Reviewed By: motiz88

Differential Revision: D43351987

fbshipit-source-id: 5cd46fdd001f3c3a3599ada44f525bec467854e1
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Handle "simple" (missing origin) source mappings in minifier output robhogan/metro
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