parse less than token rather than left shift in context of type arguments

Author: Kingwl

src/compiler/parser.ts

@@ -1093,6 +1093,10 @@ namespace ts {
             return currentToken = scanner.reScanTemplateToken();
         }
 
+        function reScanLessThanToken(): SyntaxKind {
+            return currentToken = scanner.reScanLessThanToken();
+        }
+
         function scanJsxIdentifier(): SyntaxKind {
             return currentToken = scanner.scanJsxIdentifier();
         }
@@ -2263,7 +2267,7 @@ namespace ts {
         function parseTypeReference(): TypeReferenceNode {
             const node = <TypeReferenceNode>createNode(SyntaxKind.TypeReference);
             node.typeName = parseEntityName(/*allowReservedWords*/ true, Diagnostics.Type_expected);
-            if (!scanner.hasPrecedingLineBreak() && token() === SyntaxKind.LessThanToken) {
+            if (!scanner.hasPrecedingLineBreak() && reScanLessThanToken() === SyntaxKind.LessThanToken) {
                 node.typeArguments = parseBracketedList(ParsingContext.TypeArguments, parseType, SyntaxKind.LessThanToken, SyntaxKind.GreaterThanToken);
             }
             return finishNode(node);

src/compiler/scanner.ts

@@ -31,6 +31,7 @@ namespace ts {
         scanJsxIdentifier(): SyntaxKind;
         scanJsxAttributeValue(): SyntaxKind;
         reScanJsxToken(): JsxTokenSyntaxKind;
+        reScanLessThanToken(): SyntaxKind;
         scanJsxToken(): JsxTokenSyntaxKind;
         scanJSDocToken(): JsDocSyntaxKind;
         scan(): SyntaxKind;
@@ -845,6 +846,7 @@ namespace ts {
             scanJsxIdentifier,
             scanJsxAttributeValue,
             reScanJsxToken,
+            reScanLessThanToken,
             scanJsxToken,
             scanJSDocToken,
             scan,
@@ -1840,6 +1842,14 @@ namespace ts {
             return token = scanJsxToken();
         }
 
+        function reScanLessThanToken(): SyntaxKind {
+            if (token === SyntaxKind.LessThanLessThanToken) {
+                pos = tokenPos + 1;
+                return token = SyntaxKind.LessThanToken;
+            }
+            return token;
+        }
+
         function scanJsxToken(): JsxTokenSyntaxKind {
             startPos = tokenPos = pos;
 

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -3071,6 +3071,7 @@ declare namespace ts {
         scanJsxIdentifier(): SyntaxKind;
         scanJsxAttributeValue(): SyntaxKind;
         reScanJsxToken(): JsxTokenSyntaxKind;
+        reScanLessThanToken(): SyntaxKind;
         scanJsxToken(): JsxTokenSyntaxKind;
         scanJSDocToken(): JsDocSyntaxKind;
         scan(): SyntaxKind;

tests/baselines/reference/api/typescript.d.ts

@@ -3071,6 +3071,7 @@ declare namespace ts {
         scanJsxIdentifier(): SyntaxKind;
         scanJsxAttributeValue(): SyntaxKind;
         reScanJsxToken(): JsxTokenSyntaxKind;
+        reScanLessThanToken(): SyntaxKind;
         scanJsxToken(): JsxTokenSyntaxKind;
         scanJSDocToken(): JsDocSyntaxKind;
         scan(): SyntaxKind;

tests/baselines/reference/parseGenericArrowRatherThanLeftShift.js

@@ -0,0 +1,7 @@
+//// [parseGenericArrowRatherThanLeftShift.ts]
+type Bar = ReturnType<<T>(x: T) => number>;
+
+declare const a: Bar;
+
+
+//// [parseGenericArrowRatherThanLeftShift.js]

tests/baselines/reference/parseGenericArrowRatherThanLeftShift.symbols

@@ -0,0 +1,12 @@
+=== tests/cases/compiler/parseGenericArrowRatherThanLeftShift.ts ===
+type Bar = ReturnType<<T>(x: T) => number>;
+>Bar : Symbol(Bar, Decl(parseGenericArrowRatherThanLeftShift.ts, 0, 0))
+>ReturnType : Symbol(ReturnType, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(parseGenericArrowRatherThanLeftShift.ts, 0, 23))
+>x : Symbol(x, Decl(parseGenericArrowRatherThanLeftShift.ts, 0, 26))
+>T : Symbol(T, Decl(parseGenericArrowRatherThanLeftShift.ts, 0, 23))
+
+declare const a: Bar;
+>a : Symbol(a, Decl(parseGenericArrowRatherThanLeftShift.ts, 2, 13))
+>Bar : Symbol(Bar, Decl(parseGenericArrowRatherThanLeftShift.ts, 0, 0))
+

tests/baselines/reference/parseGenericArrowRatherThanLeftShift.types

@@ -0,0 +1,8 @@
+=== tests/cases/compiler/parseGenericArrowRatherThanLeftShift.ts ===
+type Bar = ReturnType<<T>(x: T) => number>;
+>Bar : number
+>x : T
+
+declare const a: Bar;
+>a : number
+

tests/cases/compiler/parseGenericArrowRatherThanLeftShift.ts

@@ -0,0 +1,3 @@
+type Bar = ReturnType<<T>(x: T) => number>;
+
+declare const a: Bar;