c++: Fix null deref in maybe_diagnose_standard_trait [PR121859]

A static member template doesn't always have a DECL_INITIAL, as in the
below testcase, and so checking its TREE_CODE performs a null-pointer
dereference.  I don't think we need to specially detect this case as
traits we care about are unlikely to be members, so this just adds the
missing null check.

	PR c++/121859

gcc/cp/ChangeLog:

	* constraint.cc (maybe_diagnose_standard_trait): Check if expr
	is non-null.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-traits5.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 4b20b791e5d17b5d19cec373fb82e759734419ff..309ebc8132432109ee6f616ea60347a29805a3d1 100644 (file)
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3360,7 +3360,7 @@ maybe_diagnose_standard_trait (location_t loc, tree expr)
        }
     }
 
-  if (TREE_CODE (expr) == TRAIT_EXPR)
+  if (expr && TREE_CODE (expr) == TRAIT_EXPR)
     {
       diagnose_trait_expr (loc, expr, args);
       return true;

diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-traits5.C b/gcc/testsuite/g++.dg/cpp2a/concepts-traits5.C
new file mode 100644 (file)
index 0000000..de99dcd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-traits5.C
@@ -0,0 +1,14 @@
+// PR c++/121859
+// { dg-do compile { target c++20 } }
+
+template <typename T>
+struct S {
+  template <typename U>
+  static constexpr bool foo = sizeof(T) == sizeof(U);
+};
+
+template <typename U> void bar(U x) requires S<char>::foo<U> {}
+
+int main() {
+  bar(double{});  // { dg-error "no matching function" }
+}