From bd6c04fe20c8a02ba066668b9e555dda05706d23 Mon Sep 17 00:00:00 2001
From: Rintaro Ishizaki <rishizaki@apple.com>
Date: Fri, 2 May 2025 17:09:13 -0700
Subject: [PATCH] [Parse] Parse operator function with value generics

Operator function parsing has a heuristics to determine if `<` a part of
the operator name or the generic parameter clause. Handle `let` there
because value generics uses it.

rdar://149556573
(cherry picked from commit 682d2634baba3bb442c4d1926d3448463e6c5516)
---
 lib/Parse/ParseDecl.cpp        | 8 ++++----
 test/Sema/value_generics.swift | 2 ++
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index 4b420556499b6..8c821d20b5660 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -8737,12 +8737,12 @@ ParserResult<FuncDecl> Parser::parseDeclFunc(SourceLoc StaticLoc,
   SourceLoc NameLoc;
   if (Tok.isAnyOperator() || Tok.isAny(tok::exclaim_postfix, tok::amp_prefix)) {
     // If the name is an operator token that ends in '<' and the following token
-    // is an identifier, split the '<' off as a separate token. This allows
-    // things like 'func ==<T>(x:T, y:T) {}' to parse as '==' with generic type
-    // variable '<T>' as expected.
+    // is an identifier or 'let', split the '<' off as a separate token. This
+    // allows things like 'func ==<T>(x:T, y:T) {}' to parse as '==' with
+    // generic type variable '<T>' as expected.
     auto NameStr = Tok.getText();
     if (NameStr.size() > 1 && NameStr.back() == '<' &&
-        peekToken().is(tok::identifier)) {
+        peekToken().isAny(tok::identifier, tok::kw_let)) {
       NameStr = NameStr.slice(0, NameStr.size() - 1);
     }
     SimpleName = Context.getIdentifier(NameStr);
diff --git a/test/Sema/value_generics.swift b/test/Sema/value_generics.swift
index 0f5d38b9dce15..e387d04f3f5f7 100644
--- a/test/Sema/value_generics.swift
+++ b/test/Sema/value_generics.swift
@@ -51,6 +51,8 @@ func c<let M: Int>(with a: A<M>) {} // OK
 func d<T>(with a: A<T>) {} // expected-error {{cannot pass type 'T' as a value for generic value 'N'}}
 func e(with a: A<Int>) {} // expected-error {{cannot pass type 'Int' as a value for generic value 'N'}}
 
+func *<let X: Int, let Y: Int>(l: A<X>, r: A<Y>) -> Int { l.int * r.int }
+
 struct Generic<T: ~Copyable & ~Escapable> {}
 struct GenericWithIntParam<T: ~Copyable & ~Escapable, let N: Int> {}