generate "names" in source maps (#2415)

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+* Emit `names` in source maps ([#1296](https://github.com/evanw/esbuild/issues/1296))
+
+    The [source map specification](https://sourcemaps.info/spec.html) includes an optional `names` field that can associate an identifier with a mapping entry. This can be used to record the original name for an identifier, which is useful if the identifier was renamed to something else in the generated code. When esbuild was originally written, this field wasn't widely used, but now there are some debuggers that make use of it to provide better debugging of minified code. With this release, esbuild now includes a `names` field in the source maps that it generates. To save space, the original name is only recorded when it's different from the final name.
+
 * Update parser for arrow functions with initial default type parameters in `.tsx` files ([#2410](https://github.com/evanw/esbuild/issues/2410))
 
     TypeScript 4.6 introduced a [change to the parsing of JSX syntax in `.tsx` files](https://github.com/microsoft/TypeScript/issues/47062). Now a `<` token followed by an identifier and then a `=` token is parsed as an arrow function with a default type parameter instead of as a JSX element. This release updates esbuild's parser to match TypeScript's parser.

internal/bundler/linker.go

@@ -5950,6 +5950,7 @@ func (c *linkerContext) generateSourceMapForChunk(
 	mappingsStart := j.Length()
 	prevEndState := sourcemap.SourceMapState{}
 	prevColumnOffset := 0
+	totalQuotedNameLen := 0
 	for _, result := range results {
 		chunk := result.sourceMapChunk
 		offset := result.generatedOffset
@@ -5971,6 +5972,7 @@ func (c *linkerContext) generateSourceMapForChunk(
 			SourceIndex:     sourcesIndex,
 			GeneratedLine:   offset.Lines,
 			GeneratedColumn: offset.Columns,
+			OriginalName:    totalQuotedNameLen,
 		}
 		if offset.Lines == 0 {
 			startState.GeneratedColumn += prevColumnOffset
@@ -5980,9 +5982,24 @@ func (c *linkerContext) generateSourceMapForChunk(
 		sourcemap.AppendSourceMapChunk(&j, prevEndState, startState, chunk.Buffer)
 
 		// Generate the relative offset to start from next time
+		prevOriginalName := prevEndState.OriginalName
 		prevEndState = chunk.EndState
 		prevEndState.SourceIndex += sourcesIndex
+		if chunk.Buffer.FirstNameOffset.IsValid() {
+			prevEndState.OriginalName += totalQuotedNameLen
+		} else {
+			// It's possible for a chunk to have mappings but for none of those
+			// mappings to have an associated name. The name is optional and is
+			// omitted when the mapping is for a non-name token or if the final
+			// and original names are the same. In that case we need to restore
+			// the previous original name end state since it wasn't modified after
+			// all. If we don't do this, then files after this will adjust their
+			// name offsets assuming that the previous generated mapping has this
+			// file's offset, which is wrong.
+			prevEndState.OriginalName = prevOriginalName
+		}
 		prevColumnOffset = chunk.FinalGeneratedColumn
+		totalQuotedNameLen += len(chunk.QuotedNames)
 
 		// If this was all one line, include the column offset from the start
 		if prevEndState.GeneratedLine == 0 {
@@ -5992,8 +6009,23 @@ func (c *linkerContext) generateSourceMapForChunk(
 	}
 	mappingsEnd := j.Length()
 
+	// Write the names
+	isFirstName := true
+	j.AddString("\",\n  \"names\": [")
+	for _, result := range results {
+		for _, quotedName := range result.sourceMapChunk.QuotedNames {
+			if isFirstName {
+				isFirstName = false
+			} else {
+				j.AddString(", ")
+			}
+			j.AddBytes(quotedName)
+		}
+	}
+	j.AddString("]")
+
 	// Finish the source map
-	j.AddString("\",\n  \"names\": []\n}\n")
+	j.AddString("\n}\n")
 	bytes := j.Done()
 
 	if !canHaveShifts {

internal/css_printer/css_printer.go

@@ -48,7 +48,7 @@ func Print(tree css_ast.AST, options Options) PrintResult {
 	p := printer{
 		options:       options,
 		importRecords: tree.ImportRecords,
-		builder:       sourcemap.MakeChunkBuilder(options.InputSourceMap, options.LineOffsetTables),
+		builder:       sourcemap.MakeChunkBuilder(options.InputSourceMap, options.LineOffsetTables, options.ASCIIOnly),
 	}
 	for _, rule := range tree.Rules {
 		p.printRule(rule, 0, false)
@@ -78,7 +78,7 @@ func (p *printer) printRule(rule css_ast.Rule, indent int32, omitTrailingSemicol
 	}
 
 	if p.options.AddSourceMappings {
-		p.builder.AddSourceMapping(rule.Loc, p.css)
+		p.builder.AddSourceMapping(rule.Loc, "", p.css)
 	}
 
 	if !p.options.MinifyWhitespace {

internal/js_parser/sourcemap_parser.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"sort"
 
+	"github.com/evanw/esbuild/internal/ast"
 	"github.com/evanw/esbuild/internal/helpers"
 	"github.com/evanw/esbuild/internal/js_ast"
 	"github.com/evanw/esbuild/internal/logger"
@@ -26,6 +27,7 @@ func ParseSourceMap(log logger.Log, source logger.Source) *sourcemap.SourceMap {
 
 	var sources []string
 	var sourcesContent []sourcemap.SourceContent
+	var names []string
 	var mappingsRaw []uint16
 	var mappingsStart int32
 	hasVersion := false
@@ -75,6 +77,18 @@ func ParseSourceMap(log logger.Log, source logger.Source) *sourcemap.SourceMap {
 					}
 				}
 			}
+
+		case "names":
+			if value, ok := prop.ValueOrNil.Data.(*js_ast.EArray); ok {
+				names = nil
+				for _, item := range value.Items {
+					if element, ok := item.Data.(*js_ast.EString); ok {
+						names = append(names, helpers.UTF16ToString(element.Value))
+					} else {
+						names = append(names, "")
+					}
+				}
+			}
 		}
 	}
 
@@ -91,11 +105,13 @@ func ParseSourceMap(log logger.Log, source logger.Source) *sourcemap.SourceMap {
 	var mappings mappingArray
 	mappingsLen := len(mappingsRaw)
 	sourcesLen := len(sources)
+	namesLen := len(names)
 	var generatedLine int32
 	var generatedColumn int32
 	var sourceIndex int32
 	var originalLine int32
 	var originalColumn int32
+	var originalName int32
 	current := 0
 	errorText := ""
 	errorLen := 0
@@ -190,8 +206,16 @@ func ParseSourceMap(log logger.Log, source logger.Source) *sourcemap.SourceMap {
 		}
 		current += i
 
-		// Ignore the optional name index
-		if _, i, ok := sourcemap.DecodeVLQUTF16(mappingsRaw[current:]); ok {
+		// Read the original name
+		var optionalName ast.Index32
+		if originalNameDelta, i, ok := sourcemap.DecodeVLQUTF16(mappingsRaw[current:]); ok {
+			originalName += originalNameDelta
+			if originalName < 0 || originalName >= int32(namesLen) {
+				errorText = fmt.Sprintf("Invalid name index value: %d", originalName)
+				errorLen = i
+				break
+			}
+			optionalName = ast.MakeIndex32(uint32(originalName))
 			current += i
 		}
 
@@ -213,6 +237,7 @@ func ParseSourceMap(log logger.Log, source logger.Source) *sourcemap.SourceMap {
 			SourceIndex:     sourceIndex,
 			OriginalLine:    originalLine,
 			OriginalColumn:  originalColumn,
+			OriginalName:    optionalName,
 		})
 	}
 
@@ -235,6 +260,7 @@ func ParseSourceMap(log logger.Log, source logger.Source) *sourcemap.SourceMap {
 		Sources:        sources,
 		SourcesContent: sourcesContent,
 		Mappings:       mappings,
+		Names:          names,
 	}
 }