[Clang] omit parentheses in fold expressions with a single expansion

clang/docs/ReleaseNotes.rst

@@ -378,6 +378,8 @@ Improvements to Clang's diagnostics
 
 - Clang now emits a diagnostic note at the class declaration when the method definition does not match any declaration (#GH110638).
 
+- Clang now omits warnings for extra parentheses in fold expressions with single expansion (#GH101863).
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/lib/Sema/TreeTransform.h

@@ -15609,6 +15609,14 @@ TreeTransform<Derived>::TransformCXXFoldExpr(CXXFoldExpr *E) {
       return true;
   }
 
+  // When there's only one expansion, the parentheses can be safely eliminated
+  // to avoid any extra redundancy that may result in incorrect checks.
+  // For example, transforming (((args == 0) || ...)) into (args == 0)
+  // allows the omission of parentheses while ensuring precise representation
+  // and avoiding warnings regarding redundant parentheses.
+  if (*NumExpansions == 1 && !E->isTypeDependent())
+    Pattern = Pattern->IgnoreParens();
+
   for (unsigned I = 0; I != *NumExpansions; ++I) {
     Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(
         getSema(), LeftFold ? I : *NumExpansions - I - 1);
@@ -15666,7 +15674,6 @@ TreeTransform<Derived>::TransformCXXFoldExpr(CXXFoldExpr *E) {
   if (Result.isUnset())
     return getDerived().RebuildEmptyCXXFoldExpr(E->getEllipsisLoc(),
                                                 E->getOperator());
-
   return Result;
 }
 

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 +144,41 @@ void test() {
   f(S()); // expected-note {{in instantiation}}
 }
 }
+
+namespace GH101863 {
+void t1(auto... args) {
+  if (((args == 0) or ...)) { }
+}
+
+template <typename... Args>
+void t2(Args... args) {
+    if (((args == 0) or ...)) { }
+}
+
+void t3(auto... args) {
+  if ((... && (args == 0))) { }
+}
+
+void t4(auto... a, auto... b) {
+  if (((a == 0) or ...) && ((b == 0) or ...)) { }
+}
+
+void t5(auto... args) {
+  if ((((args == 0) or ...))) { }
+}
+
+void t6(auto a, auto... b) {
+    static_assert(__is_same_as(decltype((a)), int&));
+    static_assert(__is_same_as(decltype(((b), ...)), int&));
+};
+
+void test() {
+  t1(0, 1);
+  t2<>();
+  t3(1, 2, 3);
+  t3(0, 1);
+  t4(0, 1);
+  t5(0, 1);
+  t6(0, 0);
+}
+}