fix #1016: parse issue with ts arrow return types

CHANGELOG.md

@@ -1,5 +1,17 @@
 # Changelog
 
+## Unreleased
+
+* Fix a TypeScript parsing edge case with arrow function return types ([#1016](https://github.com/evanw/esbuild/issues/1016))
+
+    This release fixes the following TypeScript parsing edge case:
+
+    ```ts
+    ():Array<number>=>{return [1]}
+    ```
+
+    This was tripping up esbuild's TypeScript parser because the `>=` token was split into a `>` token and a `=` token because the `>` token is needed to close the type parameter list, but the `=` token was not being combined with the following `>` token to form a `=>` token. This is normally not an issue because there is normally a space in between the `>` and the `=>` tokens here. The issue only happened when the spaces were removed. This bug has been fixed. Now after the `>=` token is split, esbuild will expand the `=` token into the following characters if possible, which can result in a `=>`, `==`, or `===` token.
+
 ## 0.9.5
 
 * Fix parsing of the `[dir]` placeholder ([#1013](https://github.com/evanw/esbuild/issues/1013))

internal/js_lexer/js_lexer.go

@@ -437,6 +437,7 @@ func (lexer *Lexer) ExpectLessThan(isInsideJSXElement bool) {
 	case TLessThanEquals:
 		lexer.Token = TEquals
 		lexer.start++
+		lexer.maybeExpandEquals()
 
 	case TLessThanLessThan:
 		lexer.Token = TLessThan
@@ -466,6 +467,7 @@ func (lexer *Lexer) ExpectGreaterThan(isInsideJSXElement bool) {
 	case TGreaterThanEquals:
 		lexer.Token = TEquals
 		lexer.start++
+		lexer.maybeExpandEquals()
 
 	case TGreaterThanGreaterThan:
 		lexer.Token = TGreaterThan
@@ -488,6 +490,26 @@ func (lexer *Lexer) ExpectGreaterThan(isInsideJSXElement bool) {
 	}
 }
 
+func (lexer *Lexer) maybeExpandEquals() {
+	switch lexer.codePoint {
+	case '>':
+		// "=" + ">" = "=>"
+		lexer.Token = TEqualsGreaterThan
+		lexer.step()
+
+	case '=':
+		// "=" + "=" = "=="
+		lexer.Token = TEqualsEquals
+		lexer.step()
+
+		if lexer.Token == '=' {
+			// "=" + "==" = "==="
+			lexer.Token = TEqualsEqualsEquals
+			lexer.step()
+		}
+	}
+}
+
 func IsIdentifier(text string) bool {
 	if len(text) == 0 {
 		return false

internal/js_parser/ts_parser_test.go

@@ -169,6 +169,10 @@ func TestTSTypes(t *testing.T) {
 	expectPrintedTS(t, "let x: A.B<X.Y<Z<T>>>", "let x;\n")
 	expectPrintedTS(t, "let x: A.B<X.Y<Z<T>>>=2", "let x = 2;\n")
 
+	expectPrintedTS(t, "(): A<T>=> 0", "() => 0;\n")
+	expectPrintedTS(t, "(): A<B<T>>=> 0", "() => 0;\n")
+	expectPrintedTS(t, "(): A<B<C<T>>>=> 0", "() => 0;\n")
+
 	expectPrintedTS(t, "let foo: any\n<x>y", "let foo;\ny;\n")
 	expectPrintedTSX(t, "let foo: any\n<x>y</x>", "let foo;\n/* @__PURE__ */ React.createElement(\"x\", null, \"y\");\n")
 	expectParseErrorTS(t, "let foo: (any\n<x>y)", "<stdin>: error: Expected \")\" but found \"<\"\n")
@@ -1472,7 +1476,7 @@ func TestTSJSX(t *testing.T) {
 
 	expectPrintedTSX(t, "const x = <Foo<T>></Foo>", "const x = /* @__PURE__ */ React.createElement(Foo, null);\n")
 	expectPrintedTSX(t, "const x = <Foo<T> data-foo></Foo>", "const x = /* @__PURE__ */ React.createElement(Foo, {\n  \"data-foo\": true\n});\n")
-	expectParseErrorTSX(t, "const x = <Foo<T>=>", "<stdin>: error: Expected \">\" but found \"=\"\n")
+	expectParseErrorTSX(t, "const x = <Foo<T>=>", "<stdin>: error: Expected \">\" but found \"=>\"\n")
 
 	expectPrintedTS(t, "const x = <T>() => {}", "const x = () => {\n};\n")
 	expectPrintedTS(t, "const x = <T>(y)", "const x = y;\n")