[clang] [Clang] omit parentheses in fold expressions with a single expansion (PR #110761)

[Oleksandr T. via cfe-commits]

https://github.com/a-tarasyuk created https://github.com/llvm/llvm-project/pull/110761

Fixes #101863

>From 9c69d6584d6b71554aec55f0de52abb4baa9435f Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk at outlook.com>
Date: Wed, 2 Oct 2024 02:13:51 +0300
Subject: [PATCH] [Clang] omit parentheses in fold expressions with a single
 expansion

---
 clang/docs/ReleaseNotes.rst                          |  1 +
 clang/lib/Sema/TreeTransform.h                       |  3 +++
 clang/test/SemaCXX/warn-assignment-condition.cpp     | 12 +++++++++++-
 .../test/SemaTemplate/instantiate-requires-expr.cpp  |  2 +-
 4 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index bf128e370b076e..254779dc734dea 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -460,6 +460,7 @@ Bug Fixes to C++ Support
   containing outer unexpanded parameters were not correctly expanded. (#GH101754)
 - Fixed a bug in constraint expression comparison where the ``sizeof...`` expression was not handled properly
   in certain friend declarations. (#GH93099)
+- Fixed warnings for extra parentheses in fold expressions by eliminating them in single expansion cases. (#GH101863)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 6fdb18d51acef9..1a963858d0a3e4 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -15598,6 +15598,9 @@ TreeTransform<Derived>::TransformCXXFoldExpr(CXXFoldExpr *E) {
     return getDerived().RebuildEmptyCXXFoldExpr(E->getEllipsisLoc(),
                                                 E->getOperator());
 
+  if (*NumExpansions == 1)
+    Result = Result.get()->IgnoreParens();
+
   return Result;
 }
 
diff --git a/clang/test/SemaCXX/warn-assignment-condition.cpp b/clang/test/SemaCXX/warn-assignment-condition.cpp
index 09084e36bb4916..1b644260aa61d5 100644
--- a/clang/test/SemaCXX/warn-assignment-condition.cpp
+++ b/clang/test/SemaCXX/warn-assignment-condition.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -Wparentheses -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wparentheses -std=c++2a -verify %s
 
 struct A {
   int foo();
@@ -144,3 +144,13 @@ void test() {
   f(S()); // expected-note {{in instantiation}}
 }
 }
+
+namespace GH101863 {
+void foo(auto... args) {
+  if (((args == 0) or ...)) {} // ok
+}
+
+void bar() {
+  foo(3);
+}
+}
diff --git a/clang/test/SemaTemplate/instantiate-requires-expr.cpp b/clang/test/SemaTemplate/instantiate-requires-expr.cpp
index 20a19d731ae169..ce2c060a176045 100644
--- a/clang/test/SemaTemplate/instantiate-requires-expr.cpp
+++ b/clang/test/SemaTemplate/instantiate-requires-expr.cpp
@@ -36,7 +36,7 @@ using r1i2 = r1<char>; // expected-error {{constraints not satisfied for class t
 template<typename... Ts> requires
 false_v<requires (Ts... ts) {requires ((sizeof(ts) == 2) && ...);}>
 // expected-note at -1 {{because 'false_v<requires (short ts, unsigned short ts) { requires (sizeof (ts) == 2) && (sizeof (ts) == 2); }>'}}
-// expected-note at -2 {{because 'false_v<requires (short ts) { requires (sizeof (ts) == 2); }>' evaluated to false}}
+// expected-note at -2 {{because 'false_v<requires (short ts) { requires sizeof (ts) == 2; }>' evaluated to false}}
 struct r2 {};
 
 using r2i1 = r2<short, unsigned short>; // expected-error {{constraints not satisfied for class template 'r2' [with Ts = <short, unsigned short>]}}