oops: skip source maps for improved performance

Author: evanw

internal/bundler/linker.go

@@ -4203,6 +4203,7 @@ func (c *linkerContext) generateCodeForFileInChunkJS(
 		ConstValues:                  c.graph.ConstValues,
 		LegalComments:                c.options.LegalComments,
 		UnsupportedFeatures:          c.options.UnsupportedJSFeatures,
+		SourceMap:                    c.options.SourceMap,
 		AddSourceMappings:            addSourceMappings,
 		InputSourceMap:               inputSourceMap,
 		LineOffsetTables:             lineOffsetTables,
@@ -5324,6 +5325,7 @@ func (c *linkerContext) generateChunkCSS(chunks []chunkInfo, chunkIndex int, chu
 				MinifyWhitespace:  c.options.MinifyWhitespace,
 				ASCIIOnly:         c.options.ASCIIOnly,
 				LegalComments:     c.options.LegalComments,
+				SourceMap:         c.options.SourceMap,
 				AddSourceMappings: addSourceMappings,
 				InputSourceMap:    inputSourceMap,
 				LineOffsetTables:  lineOffsetTables,

internal/css_printer/css_printer.go

@@ -34,6 +34,7 @@ type Options struct {
 
 	MinifyWhitespace  bool
 	ASCIIOnly         bool
+	SourceMap         config.SourceMap
 	AddSourceMappings bool
 	LegalComments     config.LegalComments
 }
@@ -53,11 +54,17 @@ func Print(tree css_ast.AST, options Options) PrintResult {
 	for _, rule := range tree.Rules {
 		p.printRule(rule, 0, false)
 	}
-	return PrintResult{
+	result := PrintResult{
 		CSS:                    p.css,
 		ExtractedLegalComments: p.extractedLegalComments,
-		SourceMapChunk:         p.builder.GenerateChunk(p.css),
 	}
+	if options.SourceMap != config.SourceMapNone {
+		// This is expensive. Only do this if it's necessary. For example, skipping
+		// this if it's not needed sped up end-to-end parsing and printing of a
+		// large CSS file from 66ms to 52ms (around 25% faster).
+		result.SourceMapChunk = p.builder.GenerateChunk(p.css)
+	}
+	return result
 }
 
 func (p *printer) printRule(rule css_ast.Rule, indent int32, omitTrailingSemicolon bool) {

internal/js_printer/js_printer.go

@@ -3846,6 +3846,7 @@ type Options struct {
 	MinifySyntax        bool
 	ASCIIOnly           bool
 	LegalComments       config.LegalComments
+	SourceMap           config.SourceMap
 	AddSourceMappings   bool
 }
 
@@ -3905,9 +3906,13 @@ func Print(tree js_ast.AST, symbols js_ast.SymbolMap, r renamer.Renamer, options
 		}
 	}
 
-	return PrintResult{
+	result := PrintResult{
 		JS:                     p.js,
 		ExtractedLegalComments: p.extractedLegalComments,
-		SourceMapChunk:         p.builder.GenerateChunk(p.js),
 	}
+	if options.SourceMap != config.SourceMapNone {
+		// This is expensive. Only do this if it's necessary.
+		result.SourceMapChunk = p.builder.GenerateChunk(p.js)
+	}
+	return result
 }