fix #1809: add the "--drop:debugger" flag

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+* Add the `--drop:debugger` flag ([#1809](https://github.com/evanw/esbuild/issues/1809))
+
+    Passing this flag causes all [`debugger;` statements](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/debugger) to be removed from the output. This is similar to the `drop_debugger: true` flag available in the popular UglifyJS and Terser JavaScript minifiers.
+
 ## 0.14.9
 
 * Implement cross-module tree shaking of TypeScript enum values ([#128](https://github.com/evanw/esbuild/issues/128))

cmd/esbuild/main.go

@@ -67,6 +67,7 @@ var helpText = func(colors logger.Colors) string {
   --chunk-names=...         Path template to use for code splitting chunks
                             (default "[name]-[hash]")
   --color=...               Force use of color terminal escapes (true | false)
+  --drop:...                Remove certain constructs (debugger)
   --entry-names=...         Path template to use for entry point output paths
                             (default "[dir]/[name]", can also use "[hash]")
   --footer:T=...            Text to be appended to each output file of type T

internal/config/config.go

@@ -221,6 +221,7 @@ type Options struct {
 	KeepNames               bool
 	IgnoreDCEAnnotations    bool
 	TreeShaking             bool
+	DropDebugger            bool
 
 	Defines  *ProcessedDefines
 	TS       TSOptions

internal/js_parser/js_parser.go

@@ -371,6 +371,7 @@ type optionsThatSupportStructuralEquality struct {
 	omitRuntimeForTests     bool
 	ignoreDCEAnnotations    bool
 	treeShaking             bool
+	dropDebugger            bool
 	unusedImportsTS         config.UnusedImportsTS
 	useDefineForClassFields config.MaybeBool
 }
@@ -397,6 +398,7 @@ func OptionsFromConfig(options *config.Options) Options {
 			omitRuntimeForTests:     options.OmitRuntimeForTests,
 			ignoreDCEAnnotations:    options.IgnoreDCEAnnotations,
 			treeShaking:             options.TreeShaking,
+			dropDebugger:            options.DropDebugger,
 			unusedImportsTS:         options.UnusedImportsTS,
 			useDefineForClassFields: options.UseDefineForClassFields,
 		},
@@ -8904,9 +8906,14 @@ func (p *parser) keepStmtSymbolName(loc logger.Loc, ref js_ast.Ref, name string)
 
 func (p *parser) visitAndAppendStmt(stmts []js_ast.Stmt, stmt js_ast.Stmt) []js_ast.Stmt {
 	switch s := stmt.Data.(type) {
-	case *js_ast.SDebugger, *js_ast.SEmpty, *js_ast.SComment:
+	case *js_ast.SEmpty, *js_ast.SComment:
 		// These don't contain anything to traverse
 
+	case *js_ast.SDebugger:
+		if p.options.dropDebugger {
+			return stmts
+		}
+
 	case *js_ast.STypeScript:
 		// Erase TypeScript constructs from the output completely
 		return stmts

lib/shared/common.ts

@@ -107,6 +107,7 @@ function pushCommonFlags(flags: string[], options: CommonOptions, keys: OptionKe
   let minifySyntax = getFlag(options, keys, 'minifySyntax', mustBeBoolean);
   let minifyWhitespace = getFlag(options, keys, 'minifyWhitespace', mustBeBoolean);
   let minifyIdentifiers = getFlag(options, keys, 'minifyIdentifiers', mustBeBoolean);
+  let drop = getFlag(options, keys, 'drop', mustBeArray);
   let charset = getFlag(options, keys, 'charset', mustBeString);
   let treeShaking = getFlag(options, keys, 'treeShaking', mustBeBoolean);
   let ignoreAnnotations = getFlag(options, keys, 'ignoreAnnotations', mustBeBoolean);
@@ -134,6 +135,7 @@ function pushCommonFlags(flags: string[], options: CommonOptions, keys: OptionKe
   if (charset) flags.push(`--charset=${charset}`);
   if (treeShaking !== void 0) flags.push(`--tree-shaking=${treeShaking}`);
   if (ignoreAnnotations) flags.push(`--ignore-annotations`);
+  if (drop) for (let what of drop) flags.push(`--drop:${what}`);
 
   if (jsx) flags.push(`--jsx=${jsx}`);
   if (jsxFactory) flags.push(`--jsx-factory=${jsxFactory}`);

lib/shared/types.ts

@@ -3,6 +3,7 @@ export type Format = 'iife' | 'cjs' | 'esm';
 export type Loader = 'js' | 'jsx' | 'ts' | 'tsx' | 'css' | 'json' | 'text' | 'base64' | 'file' | 'dataurl' | 'binary' | 'default';
 export type LogLevel = 'verbose' | 'debug' | 'info' | 'warning' | 'error' | 'silent';
 export type Charset = 'ascii' | 'utf8';
+export type Drop = 'debugger';
 
 interface CommonOptions {
   /** Documentation: https://esbuild.github.io/api/#sourcemap */
@@ -21,6 +22,7 @@ interface CommonOptions {
   /** Documentation: https://esbuild.github.io/api/#target */
   target?: string | string[];
 
+  drop?: Drop[];
   /** Documentation: https://esbuild.github.io/api/#minify */
   minify?: boolean;
   /** Documentation: https://esbuild.github.io/api/#minify */

pkg/api/api.go

@@ -239,6 +239,12 @@ const (
 	TreeShakingTrue
 )
 
+type Drop uint8
+
+const (
+	DropDebugger Drop = 1 << iota
+)
+
 ////////////////////////////////////////////////////////////////////////////////
 // Build API
 
@@ -254,6 +260,7 @@ type BuildOptions struct {
 	Target  Target   // Documentation: https://esbuild.github.io/api/#target
 	Engines []Engine // Documentation: https://esbuild.github.io/api/#target
 
+	Drop              Drop
 	MinifyWhitespace  bool          // Documentation: https://esbuild.github.io/api/#minify
 	MinifyIdentifiers bool          // Documentation: https://esbuild.github.io/api/#minify
 	MinifySyntax      bool          // Documentation: https://esbuild.github.io/api/#minify
@@ -365,6 +372,7 @@ type TransformOptions struct {
 	Format     Format // Documentation: https://esbuild.github.io/api/#format
 	GlobalName string // Documentation: https://esbuild.github.io/api/#global-name
 
+	Drop              Drop
 	MinifyWhitespace  bool          // Documentation: https://esbuild.github.io/api/#minify
 	MinifyIdentifiers bool          // Documentation: https://esbuild.github.io/api/#minify
 	MinifySyntax      bool          // Documentation: https://esbuild.github.io/api/#minify

pkg/api/api_impl.go

@@ -848,6 +848,7 @@ func rebuildImpl(
 		MangleSyntax:          buildOpts.MinifySyntax,
 		RemoveWhitespace:      buildOpts.MinifyWhitespace,
 		MinifyIdentifiers:     buildOpts.MinifyIdentifiers,
+		DropDebugger:          (buildOpts.Drop & DropDebugger) != 0,
 		AllowOverwrite:        buildOpts.AllowOverwrite,
 		ASCIIOnly:             validateASCIIOnly(buildOpts.Charset),
 		IgnoreDCEAnnotations:  buildOpts.IgnoreAnnotations,
@@ -1339,6 +1340,7 @@ func transformImpl(input string, transformOpts TransformOptions) TransformResult
 		MangleSyntax:            transformOpts.MinifySyntax,
 		RemoveWhitespace:        transformOpts.MinifyWhitespace,
 		MinifyIdentifiers:       transformOpts.MinifyIdentifiers,
+		DropDebugger:            (transformOpts.Drop & DropDebugger) != 0,
 		ASCIIOnly:               validateASCIIOnly(transformOpts.Charset),
 		IgnoreDCEAnnotations:    transformOpts.IgnoreAnnotations,
 		TreeShaking:             validateTreeShaking(transformOpts.TreeShaking, false /* bundle */, transformOpts.Format),

pkg/cli/cli_impl.go

@@ -96,6 +96,22 @@ func parseOptionsImpl(
 				transformOpts.MinifyIdentifiers = true
 			}
 
+		case strings.HasPrefix(arg, "--drop:"):
+			value := arg[len("--drop:"):]
+			switch value {
+			case "debugger":
+				if buildOpts != nil {
+					buildOpts.Drop |= api.DropDebugger
+				} else {
+					transformOpts.Drop |= api.DropDebugger
+				}
+			default:
+				return cli_helpers.MakeErrorWithNote(
+					fmt.Sprintf("Invalid value %q in %q", value, arg),
+					"Valid values are \"debugger\".",
+				), nil
+			}
+
 		case strings.HasPrefix(arg, "--legal-comments="):
 			value := arg[len("--legal-comments="):]
 			var legalComments api.LegalComments
@@ -638,6 +654,7 @@ func parseOptionsImpl(
 			colon := map[string]bool{
 				"banner":        true,
 				"define":        true,
+				"drop":          true,
 				"external":      true,
 				"footer":        true,
 				"inject":        true,

scripts/js-api-tests.js

@@ -3692,6 +3692,16 @@ let transformTests = {
     assert.strictEqual(code, `console.log("ab"+c);\n`)
   },
 
+  async keepDebugger({ esbuild }) {
+    const { code } = await esbuild.transform(`if (x) debugger`, { drop: [] })
+    assert.strictEqual(code, `if (x)\n  debugger;\n`)
+  },
+
+  async dropDebugger({ esbuild }) {
+    const { code } = await esbuild.transform(`if (x) debugger`, { drop: ['debugger'] })
+    assert.strictEqual(code, `if (x)\n  ;\n`)
+  },
+
   async define({ esbuild }) {
     const define = { 'process.env.NODE_ENV': '"production"' }
     const { code } = await esbuild.transform(`console.log(process.env.NODE_ENV)`, { define })