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Optimize external source maps without full cache #40130

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Merged
merged 1 commit into from
Aug 19, 2020
Merged

Optimize external source maps without full cache #40130

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20 changes: 19 additions & 1 deletion src/compiler/emitter.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -862,6 +862,8 @@ namespace ts {
let sourceMapGenerator: SourceMapGenerator | undefined;
let sourceMapSource: SourceMapSource;
let sourceMapSourceIndex = -1;
let mostRecentlyAddedSourceMapSource: SourceMapSource;
let mostRecentlyAddedSourceMapSourceIndex = -1;

// Comments
let containerPos = -1;
Expand Down Expand Up @@ -5337,9 +5339,10 @@ namespace ts {
function emitSourcePos(source: SourceMapSource, pos: number) {
if (source !== sourceMapSource) {
const savedSourceMapSource = sourceMapSource;
const savedSourceMapSourceIndex = sourceMapSourceIndex;
setSourceMapSource(source);
emitPos(pos);
setSourceMapSource(savedSourceMapSource);
resetSourceMapSource(savedSourceMapSource, savedSourceMapSourceIndex);
}
else {
emitPos(pos);
Expand Down Expand Up @@ -5386,6 +5389,13 @@ namespace ts {

sourceMapSource = source;

if (source === mostRecentlyAddedSourceMapSource) {
// Fast path for when the new source map is the most recently added, in which case
// we use its captured index without going through the source map generator.
sourceMapSourceIndex = mostRecentlyAddedSourceMapSourceIndex;
return;
}

if (isJsonSourceMapSource(source)) {
return;
}
Expand All @@ -5394,6 +5404,14 @@ namespace ts {
if (printerOptions.inlineSources) {
sourceMapGenerator!.setSourceContent(sourceMapSourceIndex, source.text);
}

mostRecentlyAddedSourceMapSource = source;
mostRecentlyAddedSourceMapSourceIndex = sourceMapSourceIndex;
}

function resetSourceMapSource(source: SourceMapSource, sourceIndex: number) {
sourceMapSource = source;
sourceMapSourceIndex = sourceIndex;
}

function isJsonSourceMapSource(sourceFile: SourceMapSource) {
Expand Down