feat: hires boundary (#255)

README.md

@@ -107,7 +107,7 @@ Generates a [version 3 sourcemap](https://docs.google.com/document/d/1U1RGAehQwR
 * `file` - the filename where you plan to write the sourcemap
 * `source` - the filename of the file containing the original source
 * `includeContent` - whether to include the original content in the map's `sourcesContent` array
-* `hires` - whether the mapping should be high-resolution. Hi-res mappings map every single character, meaning (for example) your devtools will always be able to pinpoint the exact location of function calls and so on. With lo-res mappings, devtools may only be able to identify the correct line - but they're quicker to generate and less bulky. If sourcemap locations have been specified with `s.addSourcemapLocation()`, they will be used here.
+* `hires` - whether the mapping should be high-resolution. Hi-res mappings map every single character, meaning (for example) your devtools will always be able to pinpoint the exact location of function calls and so on. With lo-res mappings, devtools may only be able to identify the correct line - but they're quicker to generate and less bulky. You can also set `"boundary"` to generate a semi-hi-res mappings segmented per word boundary instead of per character, suitable for string semantics that are separated by words. If sourcemap locations have been specified with `s.addSourcemapLocation()`, they will be used here.
 
 The returned sourcemap has two (non-enumerable) methods attached for convenience:
 

src/index.d.ts

@@ -10,9 +10,11 @@ export interface SourceMapOptions {
    * be able to pinpoint the exact location of function calls and so on.
    * With lo-res mappings, devtools may only be able to identify the correct
    * line - but they're quicker to generate and less bulky.
+   * You can also set `"boundary"` to generate a semi-hi-res mappings segmented per word boundary
+   * instead of per character, suitable for string semantics that are separated by words.
    * If sourcemap locations have been specified with s.addSourceMapLocation(), they will be used here.
    */
-  hires?: boolean;
+  hires?: boolean | 'boundary';
   /**
    * The filename where you plan to write the sourcemap.
    */

src/utils/Mappings.js

@@ -1,3 +1,5 @@
+const wordRegex = /\w/;
+
 export default class Mappings {
 	constructor(hires) {
 		this.hires = hires;
@@ -26,10 +28,29 @@ export default class Mappings {
 	addUneditedChunk(sourceIndex, chunk, original, loc, sourcemapLocations) {
 		let originalCharIndex = chunk.start;
 		let first = true;
+		// when iterating each char, check if it's in a word boundary
+		let charInHiresBoundary = false;
 
 		while (originalCharIndex < chunk.end) {
 			if (this.hires || first || sourcemapLocations.has(originalCharIndex)) {
-				this.rawSegments.push([this.generatedCodeColumn, sourceIndex, loc.line, loc.column]);
+				const segment = [this.generatedCodeColumn, sourceIndex, loc.line, loc.column];
+
+				if (this.hires === 'boundary') {
+					// in hires "boundary", group segments per word boundary than per char
+					if (wordRegex.test(original[originalCharIndex])) {
+						// for first char in the boundary found, start the boundary by pushing a segment
+						if (!charInHiresBoundary) {
+							this.rawSegments.push(segment);
+							charInHiresBoundary = true;
+						}
+					} else {
+						// for non-word char, end the boundary by pushing a segment
+						this.rawSegments.push(segment);
+						charInHiresBoundary = false;
+					}
+				} else {
+					this.rawSegments.push(segment);
+				}
 			}
 
 			if (original[originalCharIndex] === '\n') {

test/MagicString.js

@@ -434,6 +434,41 @@ describe('MagicString', () => {
 			assert.deepEqual(map.sources, ['foo.js']);
 			assert.deepEqual(map.x_google_ignoreList, [0]);
 		});
+
+		it('generates segments per word boundary with hires "boundary"', () => {
+			const s = new MagicString('function foo(){ console.log("bar") }');
+
+			// rename bar to hello
+			s.overwrite(29, 32, 'hello');
+
+			const map = s.generateMap({
+				file: 'output.js',
+				source: 'input.js',
+				includeContent: true,
+				hires: 'boundary'
+			});
+
+			assert.equal(map.mappings, 'AAAA,QAAQ,CAAC,GAAG,CAAC,CAAC,CAAC,CAAC,OAAO,CAAC,GAAG,CAAC,CAAC,KAAG,CAAC,CAAC,CAAC');
+
+			const smc = new SourceMapConsumer(map);
+			let loc;
+
+			loc = smc.originalPositionFor({ line: 1, column: 3 });
+			assert.equal(loc.line, 1);
+			assert.equal(loc.column, 0);
+
+			loc = smc.originalPositionFor({ line: 1, column: 11 });
+			assert.equal(loc.line, 1);
+			assert.equal(loc.column, 9);
+
+			loc = smc.originalPositionFor({ line: 1, column: 29 });
+			assert.equal(loc.line, 1);
+			assert.equal(loc.column, 29);
+
+			loc = smc.originalPositionFor({ line: 1, column: 35 });
+			assert.equal(loc.line, 1);
+			assert.equal(loc.column, 33);
+		});
 	});
 
 	describe('getIndentString', () => {