ts: forbid regular decorators on declare fields

internal/bundler_tests/bundler_ts_test.go

@@ -990,14 +990,12 @@ func TestTSExperimentalDecoratorsNoConfig(t *testing.T) {
 					@x @y mUndef: any
 					@x @y mDef = 1
 					@x @y method() { return new Foo }
-					@x @y declare mDecl: any
 					@x @y accessor aUndef: any
 					@x @y accessor aDef = 1
 
 					@x @y static sUndef: any
 					@x @y static sDef = new Foo
 					@x @y static sMethod() { return new Foo }
-					@x @y static declare sDecl: any
 					@x @y static accessor asUndef: any
 					@x @y static accessor asDef = 1
 

internal/js_parser/js_parser.go

@@ -2181,10 +2181,11 @@ func (p *parser) parseProperty(startLoc logger.Loc, kind js_ast.PropertyKind, op
 						scopeIndex := len(p.scopesInOrder)
 
 						if prop, ok := p.parseProperty(startLoc, kind, opts, nil); ok &&
-							prop.Kind == js_ast.PropertyNormal && prop.ValueOrNil.Data == nil && len(opts.decorators) > 0 {
+							prop.Kind == js_ast.PropertyNormal && prop.ValueOrNil.Data == nil &&
+							(p.options.ts.Config.ExperimentalDecorators == config.True && len(opts.decorators) > 0) {
 							// If this is a well-formed class field with the "declare" keyword,
 							// only keep the declaration to preserve its side-effects when
-							// there are TypeScript decorators present:
+							// there are TypeScript experimental decorators present:
 							//
 							//   class Foo {
 							//     // Remove this
@@ -2194,6 +2195,15 @@ func (p *parser) parseProperty(startLoc logger.Loc, kind js_ast.PropertyKind, op
 							//     @decorator(console.log('side effect 2')) declare bar
 							//   }
 							//
+							// This behavior is surprisingly somehow valid with TypeScript
+							// experimental decorators, which was possibly by accident.
+							// TypeScript does not allow this with JavaScript decorators.
+							//
+							// References:
+							//
+							//   https://github.com/evanw/esbuild/issues/1675
+							//   https://github.com/microsoft/TypeScript/issues/46345
+							//
 							prop.Kind = js_ast.PropertyDeclare
 							return prop, true
 						}
@@ -6241,6 +6251,7 @@ func (p *parser) parseClass(classKeyword logger.Range, name *ast.LocRef, classOp
 
 		// Parse decorators for this property
 		firstDecoratorLoc := p.lexer.Loc()
+		scopeIndex := len(p.scopesInOrder)
 		opts.decorators = p.parseDecorators(p.currentScope, classKeyword, opts.decoratorContext)
 
 		// This property may turn out to be a type in TypeScript, which should be ignored
@@ -6261,6 +6272,9 @@ func (p *parser) parseClass(classKeyword logger.Range, name *ast.LocRef, classOp
 					hasConstructor = true
 				}
 			}
+		} else if !classOpts.isTypeScriptDeclare && len(opts.decorators) > 0 {
+			p.log.AddError(&p.tracker, logger.Range{Loc: firstDecoratorLoc, Len: 1}, "Decorators are not valid here")
+			p.discardScopesUpTo(scopeIndex)
 		}
 	}
 

internal/js_parser/ts_parser_test.go

@@ -2029,6 +2029,10 @@ func TestTSExperimentalDecorator(t *testing.T) {
 	expectParseErrorExperimentalDecoratorTS(t, "@x export @y class Foo {}", "<stdin>: ERROR: Decorators are not valid here\n")
 	expectParseErrorExperimentalDecoratorTS(t, "@x export default abstract", "<stdin>: ERROR: Decorators are not valid here\n")
 	expectParseErrorExperimentalDecoratorTS(t, "@x export @y default class {}", "<stdin>: ERROR: Decorators are not valid here\n<stdin>: ERROR: Unexpected \"default\"\n")
+
+	// TypeScript experimental decorators are actually allowed on declared fields
+	expectPrintedExperimentalDecoratorTS(t, "class Foo { @(() => {}) declare foo: any; @(() => {}) bar: any }",
+		"class Foo {\n  bar;\n}\n__decorateClass([\n  () => {\n  }\n], Foo.prototype, \"foo\", 2);\n__decorateClass([\n  () => {\n  }\n], Foo.prototype, \"bar\", 2);\n")
 }
 
 func TestTSDecorators(t *testing.T) {
@@ -2104,6 +2108,10 @@ func TestTSDecorators(t *testing.T) {
 	expectParseErrorTS(t, "@x export @y class Foo {}", "<stdin>: ERROR: Decorators are not valid here\n")
 	expectParseErrorTS(t, "@x export default abstract", "<stdin>: ERROR: Decorators are not valid here\n")
 	expectParseErrorTS(t, "@x export @y default class {}", "<stdin>: ERROR: Decorators are not valid here\n<stdin>: ERROR: Unexpected \"default\"\n")
+
+	// JavaScript decorators are not allowed on declared fields
+	expectParseErrorTS(t, "class Foo { @(() => {}) declare foo: any; @(() => {}) bar: any }",
+		"<stdin>: ERROR: Decorators are not valid here\n")
 }
 
 func TestTSTry(t *testing.T) {