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DevTools: Lazily parse indexed map sections #22415

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Sep 24, 2021
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DevTools: Lazily parse indexed map sections #22415

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22 changes: 19 additions & 3 deletions packages/react-devtools-shared/src/hooks/SourceMapConsumer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ import {decode} from 'sourcemap-codec';

import type {
IndexSourceMap,
IndexSourceMapSection,
BasicSourceMap,
MixedSourceMap,
} from './SourceMapTypes';
Expand All @@ -34,7 +35,7 @@ export type SourceMapConsumerType = {|
type Mappings = Array<Array<Array<number>>>;

export default function SourceMapConsumer(
sourceMapJSON: MixedSourceMap,
sourceMapJSON: MixedSourceMap | IndexSourceMapSection,
): SourceMapConsumerType {
if (sourceMapJSON.sections != null) {
return IndexedSourceMapConsumer(((sourceMapJSON: any): IndexSourceMap));
Expand Down Expand Up @@ -137,13 +138,22 @@ function BasicSourceMapConsumer(sourceMapJSON: BasicSourceMap) {
}: any): SourceMapConsumerType);
}

type Section = {|
+generatedColumn: number,
+generatedLine: number,
+map: MixedSourceMap,

// Lazily parsed only when/as the section is needed.
sourceMapConsumer: SourceMapConsumerType | null,
|};

function IndexedSourceMapConsumer(sourceMapJSON: IndexSourceMap) {
let lastOffset = {
line: -1,
column: 0,
};

const sections = sourceMapJSON.sections.map(section => {
const sections: Array<Section> = sourceMapJSON.sections.map(section => {
const offset = section.offset;
const offsetLine = offset.line;
const offsetColumn = offset.column;
Expand All @@ -161,7 +171,8 @@ function IndexedSourceMapConsumer(sourceMapJSON: IndexSourceMap) {
// The offset fields are 0-based, but we use 1-based indices when encoding/decoding from VLQ.
generatedLine: offsetLine + 1,
generatedColumn: offsetColumn + 1,
sourceMapConsumer: new SourceMapConsumer(section.map),
map: section.map,
sourceMapConsumer: null,
};
});

Expand Down Expand Up @@ -229,6 +240,11 @@ function IndexedSourceMapConsumer(sourceMapJSON: IndexSourceMap) {
);
}

if (section.sourceMapConsumer === null) {
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nit: use != instead of === ?

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Sorry, what do you mean?

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Do you mean == instead of ===?

In this case, it's always ether null or a SourceMapConsumer instance. (Flow typings ensure this too.)

// Lazily parse the section only when it's needed.
section.sourceMapConsumer = new SourceMapConsumer(section.map);
}

return section.sourceMapConsumer.originalPositionFor({
columnNumber,
lineNumber,
Expand Down