fix #1448: add source mappings for certain tokens

Author: evanw

CHANGELOG.md

@@ -1,5 +1,15 @@
 # Changelog
 
+## Unreleased
+
+* Add source mapping information for some non-executable tokens ([#1448](https://github.com/evanw/esbuild/issues/1448))
+
+    Code coverage tools can generate reports that tell you if any code exists that has not been run (or "covered") during your tests. You can use this information to add additional tests for code that isn't currently covered.
+
+    Some popular JavaScript code coverage tools have bugs where they incorrectly consider lines without any executable code as uncovered, even though there's no test you could possibly write that would cause those lines to be executed. For example, they apparently complain about the lines that only contain the trailing `}` token of an object literal.
+
+    With this release, esbuild now generates source mappings for some of these trailing non-executable tokens. This may not successfully work around bugs in code coverage tools because there are many non-executable tokens in JavaScript and esbuild doesn't map them all (the drawback of mapping these extra tokens is that esbuild will use more memory, build more slowly, and output a bigger source map). The true solution is to fix the bugs in the code coverage tools in the first place.
+
 ## 0.14.24
 
 * Allow `es2022` as a target environment ([#2012](https://github.com/evanw/esbuild/issues/2012))

internal/bundler/linker.go

@@ -1959,7 +1959,7 @@ func (c *linkerContext) createExportsForFile(sourceIndex uint32) {
 
 		// Add a getter property
 		var getter js_ast.Expr
-		body := js_ast.FnBody{Stmts: []js_ast.Stmt{{Loc: value.Loc, Data: &js_ast.SReturn{ValueOrNil: value}}}}
+		body := js_ast.FnBody{Block: js_ast.SBlock{Stmts: []js_ast.Stmt{{Loc: value.Loc, Data: &js_ast.SReturn{ValueOrNil: value}}}}}
 		if c.options.UnsupportedJSFeatures.Has(compat.Arrow) {
 			getter = js_ast.Expr{Data: &js_ast.EFunction{Fn: js_ast.Fn{Body: body}}}
 		} else {
@@ -3879,14 +3879,14 @@ func (c *linkerContext) generateCodeForFileInChunkJS(
 				cjsArgs = []js_ast.Expr{{Data: &js_ast.EObject{Properties: []js_ast.Property{{
 					IsMethod:   !c.options.UnsupportedJSFeatures.Has(compat.ObjectExtensions),
 					Key:        js_ast.Expr{Data: &js_ast.EString{Value: helpers.StringToUTF16(file.InputFile.Source.PrettyPath)}},
-					ValueOrNil: js_ast.Expr{Data: &js_ast.EFunction{Fn: js_ast.Fn{Args: args, Body: js_ast.FnBody{Stmts: stmts}}}},
+					ValueOrNil: js_ast.Expr{Data: &js_ast.EFunction{Fn: js_ast.Fn{Args: args, Body: js_ast.FnBody{Block: js_ast.SBlock{Stmts: stmts}}}}},
 				}}}}}
 			} else if c.options.UnsupportedJSFeatures.Has(compat.Arrow) {
 				// "__commonJS(function (exports, module) { ... })"
-				cjsArgs = []js_ast.Expr{{Data: &js_ast.EFunction{Fn: js_ast.Fn{Args: args, Body: js_ast.FnBody{Stmts: stmts}}}}}
+				cjsArgs = []js_ast.Expr{{Data: &js_ast.EFunction{Fn: js_ast.Fn{Args: args, Body: js_ast.FnBody{Block: js_ast.SBlock{Stmts: stmts}}}}}}
 			} else {
 				// "__commonJS((exports, module) => { ... })"
-				cjsArgs = []js_ast.Expr{{Data: &js_ast.EArrow{Args: args, Body: js_ast.FnBody{Stmts: stmts}}}}
+				cjsArgs = []js_ast.Expr{{Data: &js_ast.EArrow{Args: args, Body: js_ast.FnBody{Block: js_ast.SBlock{Stmts: stmts}}}}}
 			}
 			value := js_ast.Expr{Data: &js_ast.ECall{
 				Target: js_ast.Expr{Data: &js_ast.EIdentifier{Ref: c.cjsRuntimeRef}},
@@ -3947,14 +3947,14 @@ func (c *linkerContext) generateCodeForFileInChunkJS(
 				esmArgs = []js_ast.Expr{{Data: &js_ast.EObject{Properties: []js_ast.Property{{
 					IsMethod:   !c.options.UnsupportedJSFeatures.Has(compat.ObjectExtensions),
 					Key:        js_ast.Expr{Data: &js_ast.EString{Value: helpers.StringToUTF16(file.InputFile.Source.PrettyPath)}},
-					ValueOrNil: js_ast.Expr{Data: &js_ast.EFunction{Fn: js_ast.Fn{Body: js_ast.FnBody{Stmts: stmts}, IsAsync: isAsync}}},
+					ValueOrNil: js_ast.Expr{Data: &js_ast.EFunction{Fn: js_ast.Fn{Body: js_ast.FnBody{Block: js_ast.SBlock{Stmts: stmts}}, IsAsync: isAsync}}},
 				}}}}}
 			} else if c.options.UnsupportedJSFeatures.Has(compat.Arrow) {
 				// "__esm(function () { ... })"
-				esmArgs = []js_ast.Expr{{Data: &js_ast.EFunction{Fn: js_ast.Fn{Body: js_ast.FnBody{Stmts: stmts}, IsAsync: isAsync}}}}
+				esmArgs = []js_ast.Expr{{Data: &js_ast.EFunction{Fn: js_ast.Fn{Body: js_ast.FnBody{Block: js_ast.SBlock{Stmts: stmts}}, IsAsync: isAsync}}}}
 			} else {
 				// "__esm(() => { ... })"
-				esmArgs = []js_ast.Expr{{Data: &js_ast.EArrow{Body: js_ast.FnBody{Stmts: stmts}, IsAsync: isAsync}}}
+				esmArgs = []js_ast.Expr{{Data: &js_ast.EArrow{Body: js_ast.FnBody{Block: js_ast.SBlock{Stmts: stmts}}, IsAsync: isAsync}}}
 			}
 			value := js_ast.Expr{Data: &js_ast.ECall{
 				Target: js_ast.Expr{Data: &js_ast.EIdentifier{Ref: c.esmRuntimeRef}},

internal/js_ast/js_ast.go

@@ -266,7 +266,7 @@ const (
 )
 
 type ClassStaticBlock struct {
-	Stmts []Stmt
+	Block SBlock
 	Loc   logger.Loc
 }
 
@@ -334,17 +334,18 @@ type Fn struct {
 }
 
 type FnBody struct {
-	Stmts []Stmt
+	Block SBlock
 	Loc   logger.Loc
 }
 
 type Class struct {
-	TSDecorators []Expr
-	Name         *LocRef
-	ExtendsOrNil Expr
-	Properties   []Property
-	ClassKeyword logger.Range
-	BodyLoc      logger.Loc
+	TSDecorators  []Expr
+	Name          *LocRef
+	ExtendsOrNil  Expr
+	Properties    []Property
+	ClassKeyword  logger.Range
+	BodyLoc       logger.Loc
+	CloseBraceLoc logger.Loc
 }
 
 type ArrayBinding struct {
@@ -432,6 +433,7 @@ func (*EImportCall) isExpr()           {}
 type EArray struct {
 	Items            []Expr
 	CommaAfterSpread logger.Loc
+	CloseBracketLoc  logger.Loc
 	IsSingleLine     bool
 	IsParenthesized  bool
 }
@@ -476,8 +478,9 @@ var EUndefinedShared = &EUndefined{}
 var EThisShared = &EThis{}
 
 type ENew struct {
-	Target Expr
-	Args   []Expr
+	Target        Expr
+	Args          []Expr
+	CloseParenLoc logger.Loc
 
 	// True if there is a comment containing "@__PURE__" or "#__PURE__" preceding
 	// this call expression. See the comment inside ECall for more details.
@@ -501,6 +504,7 @@ const (
 type ECall struct {
 	Target        Expr
 	Args          []Expr
+	CloseParenLoc logger.Loc
 	OptionalChain OptionalChain
 	IsDirectEval  bool
 
@@ -653,6 +657,7 @@ type EBigInt struct{ Value string }
 type EObject struct {
 	Properties       []Property
 	CommaAfterSpread logger.Loc
+	CloseBraceLoc    logger.Loc
 	IsSingleLine     bool
 	IsParenthesized  bool
 }
@@ -1079,7 +1084,8 @@ func (*SBreak) isStmt()         {}
 func (*SContinue) isStmt()      {}
 
 type SBlock struct {
-	Stmts []Stmt
+	Stmts         []Stmt
+	CloseBraceLoc logger.Loc
 }
 
 type SEmpty struct{}
@@ -1231,21 +1237,21 @@ type SWith struct {
 
 type Catch struct {
 	BindingOrNil Binding
-	Body         []Stmt
+	Block        SBlock
 	Loc          logger.Loc
-	BodyLoc      logger.Loc
+	BlockLoc     logger.Loc
 }
 
 type Finally struct {
-	Stmts []Stmt
+	Block SBlock
 	Loc   logger.Loc
 }
 
 type STry struct {
-	Catch   *Catch
-	Finally *Finally
-	Body    []Stmt
-	BodyLoc logger.Loc
+	Catch    *Catch
+	Finally  *Finally
+	Block    SBlock
+	BlockLoc logger.Loc
 }
 
 type Case struct {
@@ -2829,7 +2835,7 @@ func SimplifyUnusedExpr(expr Expr, isUnbound func(Ref) bool) Expr {
 				}
 
 				// Just delete "(function() {})()" completely
-				if len(target.Fn.Body.Stmts) == 0 {
+				if len(target.Fn.Body.Block.Stmts) == 0 {
 					return Expr{}
 				}
 
@@ -2839,19 +2845,19 @@ func SimplifyUnusedExpr(expr Expr, isUnbound func(Ref) bool) Expr {
 				}
 
 				// Just delete "(() => {})()" completely
-				if len(target.Body.Stmts) == 0 {
+				if len(target.Body.Block.Stmts) == 0 {
 					return Expr{}
 				}
 
-				if len(target.Body.Stmts) == 1 {
-					switch s := target.Body.Stmts[0].Data.(type) {
+				if len(target.Body.Block.Stmts) == 1 {
+					switch s := target.Body.Block.Stmts[0].Data.(type) {
 					case *SExpr:
 						if !target.IsAsync {
 							// Replace "(() => { foo() })()" with "foo()"
 							return s.Value
 						} else {
 							// Replace "(async () => { foo() })()" with "(async () => foo())()"
-							target.Body.Stmts[0].Data = &SReturn{ValueOrNil: s.Value}
+							target.Body.Block.Stmts[0].Data = &SReturn{ValueOrNil: s.Value}
 							target.PreferExpr = true
 						}