fix #3308: TS type arguments for JS decorators

CHANGELOG.md

@@ -2,6 +2,16 @@
 
 ## Unreleased
 
+* Parse TypeScript type arguments for JavaScript decorators ([#3308](https://github.com/evanw/esbuild/issues/3308))
+
+    When parsing JavaScript decorators in TypeScript (i.e. with `experimentalDecorators` disabled), esbuild previously didn't parse type arguments. Type arguments will now be parsed starting with this release. For example:
+
+    ```ts
+    @foo<number>
+    @bar<number, string>()
+    class Foo {}
+    ```
+
 * Fix glob patterns matching extra stuff at the end ([#3306](https://github.com/evanw/esbuild/issues/3306))
 
     Previously glob patterns such as `./*.js` would incorrectly behave like `./*.js*` during path matching (also matching `.js.map` files, for example). This was never intentional behavior, and has now been fixed.

internal/js_parser/js_parser.go

@@ -6626,8 +6626,14 @@ func (p *parser) parseDecorator() js_ast.Expr {
 
 	memberExpr := js_ast.Expr{Loc: nameRange.Loc, Data: &js_ast.EIdentifier{Ref: p.storeNameInRef(name)}}
 
+	// "@x<y>() class{}"
+	if p.options.ts.Parse {
+		p.skipTypeScriptTypeArguments(skipTypeScriptTypeArgumentsOpts{})
+	}
+
 	for p.lexer.Token == js_lexer.TDot {
 		p.lexer.Next()
+
 		if p.lexer.Token == js_lexer.TPrivateIdentifier {
 			memberExpr.Data = &js_ast.EIndex{
 				Target: memberExpr,
@@ -6642,6 +6648,11 @@ func (p *parser) parseDecorator() js_ast.Expr {
 			}
 			p.lexer.Expect(js_lexer.TIdentifier)
 		}
+
+		// "@x.y<z>() class{}"
+		if p.options.ts.Parse {
+			p.skipTypeScriptTypeArguments(skipTypeScriptTypeArgumentsOpts{})
+		}
 	}
 
 	// The grammar for "DecoratorMemberExpression" currently forbids "?."

internal/js_parser/ts_parser_test.go

@@ -2037,6 +2037,16 @@ func TestTSDecorators(t *testing.T) {
 	expectParseErrorTS(t, "@new Function() class Foo {}", "<stdin>: ERROR: Expected identifier but found \"new\"\n")
 	expectParseErrorTS(t, "@() => {} class Foo {}", "<stdin>: ERROR: Unexpected \")\"\n")
 
+	expectPrintedTS(t, "class Foo { @x<{}> y: any }", "class Foo {\n  @x\n  y;\n}\n")
+	expectPrintedTS(t, "class Foo { @x<{}>() y: any }", "class Foo {\n  @x()\n  y;\n}\n")
+	expectPrintedTS(t, "class Foo { @x<{}> @y<[], () => {}> z: any }", "class Foo {\n  @x\n  @y\n  z;\n}\n")
+	expectPrintedTS(t, "class Foo { @x<{}>() @y<[], () => {}>() z: any }", "class Foo {\n  @x()\n  @y()\n  z;\n}\n")
+	expectPrintedTS(t, "class Foo { @x<{}>.y<[], () => {}> z: any }", "class Foo {\n  @x.y\n  z;\n}\n")
+
+	// TypeScript 5.0+ allows this but Babel doesn't. I believe this is a bug
+	// with TypeScript: https://github.com/microsoft/TypeScript/issues/55336
+	expectParseErrorTS(t, "class Foo { @x<{}>().y<[], () => {}>() z: any }", "<stdin>: ERROR: Expected identifier but found \".\"\n")
+
 	errorText := "<stdin>: ERROR: Transforming JavaScript decorators to the configured target environment is not supported yet\n"
 	expectParseErrorWithUnsupportedFeaturesTS(t, compat.Decorators, "@dec class Foo {}", errorText)
 	expectParseErrorWithUnsupportedFeaturesTS(t, compat.Decorators, "class Foo { @dec x }", errorText)