Add Source Map sourceRoot Support

This adds the `--sourcemap-root`, `sourcemapRoot` (JS), and `SourcemapRoot` (Go) options to insert a `sourceRoot` field in any output source maps. When a `sourceRoot` exists on the map, any sources are resolved relative to it.

 This is particularly useful when hosting compiled code on a server, and pointing the source files to a GitHub repo. Eg, as [AMP does](https://cdn.ampproject.org/v0.mjs.map).

cmd/esbuild/main.go

@@ -85,6 +85,8 @@ var helpText = func(colors logger.Colors) string {
   --sourcefile=...          Set the source file for the source map (for stdin)
   --sourcemap=external      Do not link to the source map with a comment
   --sourcemap=inline        Emit the source map with an inline data URL
+  --sourcemap-root=...      The root path from which source files are looked up
+	                          in a source map.
   --sources-content=false   Omit "sourcesContent" in generated source maps
   --tree-shaking=...        Set to "ignore-annotations" to work with packages
                             that have incorrect tree-shaking annotations

internal/bundler/linker.go

@@ -4841,6 +4841,11 @@ func (c *linkerContext) generateSourceMapForChunk(
 	}
 	j.AddString("]")
 
+	if c.options.SourceMapRoot != "" {
+		j.AddString(",\n  \"sourceRoot\": ")
+		j.AddBytes(js_printer.QuoteForJSON(c.options.SourceMapRoot, c.options.ASCIIOnly))
+	}
+
 	// Write the sourcesContent
 	if !c.options.ExcludeSourcesContent {
 		j.AddString(",\n  \"sourcesContent\": [")

internal/config/config.go

@@ -237,6 +237,7 @@ type Options struct {
 	NeedsMetafile bool
 
 	SourceMap             SourceMap
+	SourceMapRoot         string
 	ExcludeSourcesContent bool
 
 	Stdin *StdinInfo

lib/common.ts

@@ -94,6 +94,7 @@ function pushLogFlags(flags: string[], options: CommonOptions, keys: OptionKeys,
 }
 
 function pushCommonFlags(flags: string[], options: CommonOptions, keys: OptionKeys): void {
+  let sourcemapRoot = getFlag(options, keys, 'sourcemapRoot', mustBeString);
   let sourcesContent = getFlag(options, keys, 'sourcesContent', mustBeBoolean);
   let target = getFlag(options, keys, 'target', mustBeStringOrArray);
   let format = getFlag(options, keys, 'format', mustBeString);
@@ -110,6 +111,7 @@ function pushCommonFlags(flags: string[], options: CommonOptions, keys: OptionKe
   let pure = getFlag(options, keys, 'pure', mustBeArray);
   let keepNames = getFlag(options, keys, 'keepNames', mustBeBoolean);
 
+  if (sourcemapRoot !== void 0) flags.push(`--sourcemap-root=${sourcemapRoot}`);
   if (sourcesContent !== void 0) flags.push(`--sources-content=${sourcesContent}`);
   if (target) {
     if (Array.isArray(target)) flags.push(`--target=${Array.from(target).map(validateTarget).join(',')}`)

lib/types.ts

@@ -7,6 +7,7 @@ export type TreeShaking = true | 'ignore-annotations';
 
 interface CommonOptions {
   sourcemap?: boolean | 'inline' | 'external' | 'both';
+  sourcemapRoot?: string;
   sourcesContent?: boolean;
 
   format?: Format;

pkg/api/api.go

@@ -223,6 +223,7 @@ type BuildOptions struct {
 	LogLevel LogLevel
 
 	Sourcemap      SourceMap
+	SourcemapRoot  string
 	SourcesContent SourcesContent
 
 	Target  Target
@@ -318,6 +319,7 @@ type TransformOptions struct {
 	LogLevel LogLevel
 
 	Sourcemap      SourceMap
+	SourcemapRoot  string
 	SourcesContent SourcesContent
 
 	Target     Target

pkg/api/api_impl.go

@@ -737,6 +737,7 @@ func rebuildImpl(
 		InjectedDefines:       injectedDefines,
 		Platform:              validatePlatform(buildOpts.Platform),
 		SourceMap:             validateSourceMap(buildOpts.Sourcemap),
+		SourceMapRoot:         buildOpts.SourcemapRoot,
 		ExcludeSourcesContent: buildOpts.SourcesContent == SourcesContentExclude,
 		MangleSyntax:          buildOpts.MinifySyntax,
 		RemoveWhitespace:      buildOpts.MinifyWhitespace,
@@ -1188,6 +1189,7 @@ func transformImpl(input string, transformOpts TransformOptions) TransformResult
 		Defines:                 defines,
 		InjectedDefines:         injectedDefines,
 		SourceMap:               validateSourceMap(transformOpts.Sourcemap),
+		SourceMapRoot:           transformOpts.SourcemapRoot,
 		ExcludeSourcesContent:   transformOpts.SourcesContent == SourcesContentExclude,
 		OutputFormat:            validateFormat(transformOpts.Format),
 		GlobalName:              validateGlobalName(log, transformOpts.GlobalName),

pkg/cli/cli_impl.go

@@ -159,6 +159,14 @@ func parseOptionsImpl(
 			}
 			hasBareSourceMapFlag = false
 
+		case strings.HasPrefix(arg, "--sourcemap-root="):
+			sourceRoot := arg[len("--sourcemap-root="):]
+			if buildOpts != nil {
+				buildOpts.SourcemapRoot = sourceRoot
+			} else {
+				transformOpts.SourcemapRoot = sourceRoot
+			}
+
 		case strings.HasPrefix(arg, "--sources-content="):
 			value := arg[len("--sources-content="):]
 			var sourcesContent api.SourcesContent

scripts/js-api-tests.js

@@ -338,6 +338,29 @@ let buildTests = {
     assert.strictEqual(json.sourcesContent, void 0)
   },
 
+  async sourceMapSourceRoot({ esbuild, testDir }) {
+    const input = path.join(testDir, 'in.js')
+    const output = path.join(testDir, 'out.js')
+    const content = 'exports.foo = 123'
+    await writeFileAsync(input, content)
+    await esbuild.build({
+      entryPoints: [input],
+      outfile: output,
+      sourcemap: true,
+      sourcemapRoot: 'https://example.com/'
+    })
+    const result = require(output)
+    assert.strictEqual(result.foo, 123)
+    const outputFile = await readFileAsync(output, 'utf8')
+    const match = /\/\/# sourceMappingURL=(.*)/.exec(outputFile)
+    assert.strictEqual(match[1], 'out.js.map')
+    const resultMap = await readFileAsync(output + '.map', 'utf8')
+    const json = JSON.parse(resultMap)
+    assert.strictEqual(json.version, 3)
+    assert.strictEqual(json.sources[0], path.basename(input))
+    assert.strictEqual(json.sourceRoot, 'https://example.com/')
+  },
+
   async sourceMapWithDisabledFile({ esbuild, testDir }) {
     const input = path.join(testDir, 'in.js')
     const disabled = path.join(testDir, 'disabled.js')
@@ -3152,6 +3175,12 @@ let transformTests = {
     await assertSourceMap(Buffer.from(base64.trim(), 'base64').toString(), 'afile.js')
   },
 
+  async sourceMapRoot({ esbuild }) {
+    const { code, map } = await esbuild.transform(`let       x`, { sourcemap: true, sourcefile: 'afile.js', sourcemapRoot: "https://example.com/" })
+    assert.strictEqual(code, `let x;\n`)
+    assert.strictEqual(JSON.parse(map).sourceRoot, 'https://example.com/');
+  },
+
   async numericLiteralPrinting({ esbuild }) {
     async function checkLiteral(text) {
       const { code } = await esbuild.transform(`return ${text}`, { minify: true })