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Editorial: add a 'decode a list of base64 VLQ' algorithm #130

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Editorial: add a 'decode a list of base64 VLQ' algorithm #130

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b8b1c4f
Editorial: add a 'decode a list of base64 VLQ' algorithm
szuend Sep 24, 2024
1755a36
Fix variable formatting.
szuend Sep 25, 2024
2ce7f3a
Mappings: Be more linient for mappings with only 2 or 3 fields
szuend Sep 26, 2024
ca59e78
Mappings: Fix variable formatting for indexed access
szuend Sep 26, 2024
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51 changes: 23 additions & 28 deletions source-map.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -497,13 +497,10 @@ sources=] <dfn for="decode source map mappings">|sources|</dfn>, run the followi
|groups|[|generatedLine|] on `,`.
1. Let |generatedColumn| be 0.
1. [=For each=] |segment| in |segments|:
1. Let |position| be a [=position variable=] for |segment|, initially pointing at
|segment|'s start.
1. [=Decode a base64 VLQ=] from |segment| given |position| and let
|relativeGeneratedColumn| be the result.
1. If |relativeGeneratedColumn| is null, [=optionally report an error=] and continue
with the next iteration.
1. Increase |generatedColumn| by |relativeGeneratedColumn|. If the result is negative,
1. [=Decode a list of base64 VLQ=] from |segment| and let |vlqs| be the result.
1. If |vlqs|'s [=list/size=] is not 1, 4 or 5, [=optionally report an error=]
and continue with the next iteration.
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1. Increase |generatedColumn| by |vlqs[0]|. If the result is negative,
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[=optionally report an error=] and continue with the next iteration.
1. Let |decodedMapping| be a new [=decoded mapping=] whose
[=decoded mapping/generatedLine=] is |generatedLine|,
Expand All @@ -513,18 +510,10 @@ sources=] <dfn for="decode source map mappings">|sources|</dfn>, run the followi
[=decoded mapping/originalColumn=] is null,
and [=decoded mapping/name=] is null.
1. Append |decodedMapping| to |decodedMappings|.
1. [=Decode a base64 VLQ=] from |segment| given |position| and let |relativeSourceIndex|
be the result.
1. [=Decode a base64 VLQ=] from |segment| given |position| and let
|relativeOriginalLine| be the result.
1. [=Decode a base64 VLQ=] from |segment| given |position| and let
|relativeOriginalColumn| be the result.
1. If |relativeOriginalColumn| is null, then:
1. If |relativeSourceIndex| is not null, [=optionally report an error=].
1. Continue with the next iteration.
1. Increase |sourceIndex| by |relativeSourceIndex|.
1. Increase |originalLine| by |relativeOriginalLine|.
1. Increase |originalColumn| by |relativeOriginalColumn|.
1. If |vlqs|'s [=list/size=] is 1, continue with the next iteration.
1. Increase |sourceIndex| by |vlqs[1]|.
1. Increase |originalLine| by |vlqs[2]|.
1. Increase |originalColumn| by |vlqs[3]|.
1. If any of |sourceIndex|, |originalLine|, or |originalColumn| are less than 0, or if
|sourceIndex| is greater than or equal to |sources|'s [=list/size=], [=optionally
report an error=].
Expand All @@ -533,15 +522,11 @@ sources=] <dfn for="decode source map mappings">|sources|</dfn>, run the followi
|sources|[|sourceIndex|].
1. Set |decodedMapping|'s [=decoded mapping/originalLine=] to |originalLine|.
1. Set |decodedMapping|'s [=decoded mapping/originalColumn=] to |originalColumn|.
1. [=Decode a base64 VLQ=] from |segment| given |position| and let |relativeNameIndex|
be the result.
1. If |relativeNameIndex| is not null, then:
1. Increase |nameIndex| by |relativeNameIndex|.
1. If |nameIndex| is negative or greater than |names|'s [=list/size=], [=optionally
report an error=].
1. Else, set |decodedMapping|'s [=decoded mapping/name=] to |names|[|nameIndex|].
1. If |position| does not point to the end of |segment|, [=optionally report an
error=].
1. If |vlqs|'s [=list/size=] is 4, continue with the next iteration.
1. Increase |nameIndex| by |vlqs[4]|.
1. If |nameIndex| is negative or greater than |names|'s [=list/size=],
[=optionally report an error=].
1. Else, set |decodedMapping|'s [=decoded mapping/name=] to |names|[|nameIndex|].
1. Increase |generatedLine| by 1.
1. Return |decodedMappings|.

Expand Down Expand Up @@ -574,6 +559,16 @@ To <dfn>decode a base64 VLQ</dfn> from a [=string=] |segment| given a [=position
NOTE: In addition to returning the decoded value, this algorithm updates the [=position variable=]
in the calling algorithm.

To <dfn>decode a list of base64 VLQ</dfn> from a [=string=] |segment|, run the following steps:
1. Let |position| be a [=position variable=] for |segment|, initially pointing at
|segment|'s start.
1. Let |vlqs| be a new empty [=list=].
1. While |position| does not point to the end of |segment|:
1. [=Decode a base64 VLQ=] from |segment| given |position| and let |vlq| be the result.
1. Assert |vlq| is not null.
1. Append |vlq| to |vlqs|.
1. Return |vlqs|.

### [=Mappings=] for generated JavaScript code

Generated code positions that may have [=Mapping=] entries are defined in terms of *input elements*
Expand Down
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