[PATCH] c++: Fix bogus -Wparentheses warning with fold-expression [PR94505]

[Marek Polacek]

We issue bogus -Wparentheses warnings (3 of them!) for this fold expression:

  ((B && true) || ...)

Firstly, issuing a warning for a compiler-generated expression is wrong
and secondly, B && true must be wrapped in ( ) otherwise you'll get
error: binary expression in operand of fold-expression.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

	PR c++/94505 - bogus -Wparentheses warning with fold-expression.
	* pt.c (fold_expression): Add warning_sentinel for -Wparentheses
	before calling build_x_binary_op.

	* g++.dg/cpp1z/fold11.C: New test.
---
 gcc/cp/pt.c                         |  1 +
 gcc/testsuite/g++.dg/cpp1z/fold11.C | 12 ++++++++++++
 2 files changed, 13 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/fold11.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 9e39f46a090..5d5941eddb7 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12356,6 +12356,7 @@ fold_expression (tree t, tree left, tree right, tsubst_flags_t complain)
   if (FOLD_EXPR_MODIFY_P (t))
     return build_x_modify_expr (input_location, left, code, right, complain);
 
+  warning_sentinel s(warn_parentheses);
   switch (code)
     {
     case COMPOUND_EXPR:
diff --git a/gcc/testsuite/g++.dg/cpp1z/fold11.C b/gcc/testsuite/g++.dg/cpp1z/fold11.C
new file mode 100644
index 00000000000..09a30555eee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/fold11.C
@@ -0,0 +1,12 @@
+// PR c++/94505 - bogus -Wparentheses warning with fold-expression.
+// { dg-do compile { target c++17 } }
+// { dg-options "-Wparentheses" }
+
+template <bool... B>
+bool foo () {
+    return ((B && true) || ...); // { dg-bogus "suggest parentheses" }
+}
+
+int main () {
+    foo<true, false, false, true> ();
+}

base-commit: fc186077486fb6e5453157ad8507c66d0a34017c
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA