Fix sourcemaps failing on refresh #1755
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DeMoorJasper
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DeMoorJasper
changed the title
src/SourceMap.js
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| @@ -38,6 +39,8 @@ class SourceMap { | |||
| } | |||
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| async addMap(map, lineOffset = 0, columnOffset = 0) { | |||
| map = clone(map); | |||
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what kind of perf impact does this have? is there a specific situation where we need to clone, or just all the time?
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We could probably move it to before line 62, as the actual reuse of mappings happens on the lines after that as far as I know. I haven't tested moving it, but it should work in theory
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I'm not able to compare performance as I don't really have a project which is big enough to notice a difference
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where do we mutate the mappings? |
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Tested perf on a larger app, and it was noticeable - about 5 seconds slower build time. Changed it to manually clone each mapping, and this reduced the time to about the same again. |
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Awesome, thanks for testing it out :) |
| }; | ||
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| this.mappings.push(mapping); | ||
| this.mappings.push({ |
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Not familiar with this API, but does this mapping have a .name? I see it used in addConsumerMapping, but not this one.
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Ow it should, thanks for noticing
| line: mapping.generated.line + lineOffset, | ||
| column: mapping.generated.column + columnOffset | ||
| } | ||
| }); | ||
| } | ||
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| addConsumerMapping(mapping, lineOffset = 0, columnOffset = 0) { |
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FYI, the handling below here seems questionable. Mappings with no original location are still important because they terminate the end of a conceptual range over the generated file by saying that a generated location points at nothing. By discarding mappings with no original location, you're essentially force-extending every generated mapping to instead extend to the end of the line/next original-location mapping.
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Not sure why this would be an issue, if code is generated it shouldn't have a mapping right?
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Not quite. Sourcemaps are conceptually ranges over the generated code, but the actual mappings passed from the consumer are single points of data, from one generated line/col to an original line/col (optionally).
It's the fact that the original part is option that is critical here, and that is getting lost with the check in
if (
!mapping.source ||
!mapping.originalLine ||
(!mapping.originalColumn && mapping.originalColumn !== 0)
) {
return;
}
Imagine a generated piece of code like this:
console.log
If I want to map just the console to something in the original JS file, setting no original location on the .log part, I'd generate two mappings. One would say
{
generated: {
line: 0,
column: 0,
},
original: {
line: 0,
column: 0,
},
source: "input.js",
name: "console",
}
to say that the start of the word "console" (line 0, column 0) maps to the original file, also at line 0 column 0.
So far so good, but nothing sets an end position, so that mapping on its own would also apply to the .log part.
That's where non-source mappings come in. You'd also include a mapping as
{
generated: {
line: 0,
column: 7,
},
original: null
source: null,
name: null,
}
to say that, starting at line 0, column 7, the code maps to nothing in the original file.
By discarding that information, you've essentially made the original line 0 column 0 mapping apply to the whole of console.log.
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Ow I never saw that as an issue but I'll definitely look into it.
Now that you've explained it, I can see it could and will cause issues.
Thank you
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No problem, I'm happy to answer any other sourcemap questions if you have them. Babel has had it's fair share of questionable mapping logic over the ears too.
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when is this supposed to be fixed? i need this and it still breaks in "parcel-bundler": "1.10.0-beta.1 |
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Still having this issue with new typescript project and fresh install of parcel |
Sourcemaps inside assets were being overwritten due to not cloning the actual mappings array before merging and manipulating them inside the packager. Which caused the sourcemaps to get their position + bundle offset, resulting in incorrect mappings
Closes #997