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Merged
takikawa merged 4 commits into from
Apr 15, 2026
Merged

Range mappings: Change index encoding to start at 0 #252

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ab18a2b
Change range mapping index encoding to start at 0
takikawa Apr 8, 2026
96dd96b
Fix detection of duplicate range mapping offsets
takikawa Apr 15, 2026
44f8372
Add missing empty RangeMappingLine case
takikawa Apr 15, 2026
4eb9ae7
Minor fix: replace not equal sign with "is not"
takikawa Apr 15, 2026
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45 changes: 38 additions & 7 deletions spec.emu
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Original file line number Diff line number Diff line change
Expand Up @@ -572,7 +572,7 @@
"sourcesContent": [null, null],
"names": ["src", "maps", "are", "fun"],
"mappings": "A,AAAB;;ABCDE",
"rangeMappings": "C;;B",
"rangeMappings": "B;;A",
"ignoreList": [0]
}
</code></pre>
Expand Down Expand Up @@ -1160,7 +1160,29 @@
</table>
</emu-table>

<p>A <dfn id="decode-range-mappings-state-record" variants="Decode Range Mappings State Records">Decode Range Mappings State Record</dfn> has the same fields as a Decoded Range Mapping Offset Record.</p>
<p>A <dfn id="decode-range-mappings-state-record" variants="Decode Range Mappings State Records">Decode Range Mappings State Record</dfn> has the following fields.</p>
<emu-table id="table-decode-range-mapping-state-record-fields" caption="Fields of Decode Range Mappings State Records">
<table>
<thead>
<tr>
<th>
Field Name
</th>
<th>
Value Type
</th>
</tr>
</thead>
<tr>
<td>[[GeneratedLine]]</td>
<td>a non-negative integer</td>
</tr>
<tr>
<td>[[MappingIndex]]</td>
<td>a non-negative integer or ~none~</td>
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@jridgewell jridgewell Apr 15, 2026 •
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Alternatively we could allow this to be negative, initialize to -1, and verify it's positive in appending the new Range Mapping Offset Record.

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@nicolo-ribaudo nicolo-ribaudo Apr 15, 2026

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I prefer ~none~, as it makes the intent clearer when reading.

</tr>
</table>
</emu-table>

<emu-clause id="sec-range-mappings-grammar">
<h1>Range mappings grammar</h1>
Expand Down Expand Up @@ -1201,9 +1223,15 @@
<emu-alg>
1. Perform DecodeRangeMappingsField of |RangeMappingLine| with arguments _state_ and _rangeMappings_.
1. Set _state_.[[GeneratedLine]] to _state_.[[GeneratedLine]] + 1.
1. Set _state_.[[MappingIndex]] to 0.
1. Set _state_.[[MappingIndex]] to ~none~.
1. Perform DecodeRangeMappingsField of |RangeMappingLineList| with arguments _state_ and _rangeMappings_.
</emu-alg>
<emu-grammar>
RangeMappingLine : [empty]
</emu-grammar>
<emu-alg>
1. Return.
</emu-alg>
<emu-grammar>
RangeMappingList :
RangeMapping RangeMappingList
Expand All @@ -1218,10 +1246,13 @@
</emu-grammar>
<emu-alg>
1. Let _relativeIndex_ be the VLQUnsignedValue of |Vlq|.
1. If _relativeIndex_ is 0, then
1. If _relativeIndex_ = 0 and _state_.[[MappingIndex]] is not ~none~, then
1. Optionally report an error.
1. Set _state_.[[MappingIndex]] to _state_.[[MappingIndex]] + _relativeIndex_.
1. Let _rangeMappingOffset_ be a new Decoded Range Mapping Offset Record { [[GeneratedLine]]: _state_.[[GeneratedLine]], [[MappingIndex]]: _state_.[[MappingIndex]] - 1 }.
1. If _state_.[[MappingIndex]] is ~none~, then
1. Set _state_.[[MappingIndex]] to _relativeIndex_.
1. Else,
1. Set _state_.[[MappingIndex]] to _state_.[[MappingIndex]] + _relativeIndex_.
1. Let _rangeMappingOffset_ be a new Decoded Range Mapping Offset Record { [[GeneratedLine]]: _state_.[[GeneratedLine]], [[MappingIndex]]: _state_.[[MappingIndex]] }.
1. Append _rangeMappingOffset_ to _rangeMappings_.
</emu-alg>
</emu-clause>
Expand All @@ -1240,7 +1271,7 @@
1. If parsing failed, then
1. Optionally report an error.
1. Return _rangeMappings_.
1. Let _state_ be a new Decode Range Mappings State Record with all fields set to 0.
1. Let _state_ be a new Decode Range Mappings State Record { [[GeneratedLine]]: 0, [[MappingIndex]]: ~none~ }.
1. Perform DecodeRangeMappingsField of _rangeMappingsNode_ with arguments _state_ and _rangeMappings_.
1. Return _rangeMappings_.
</emu-alg>
Expand Down
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