[gcc r17-2303] gcc/cp-tree: require that temp_override deduces on first constructor arg

https://gcc.gnu.org/g:3a578f6fcb8b9e1b84584dc8a789dafa80c9e2ae

commit r17-2303-g3a578f6fcb8b9e1b84584dc8a789dafa80c9e2ae
Author: Arsen Arsenović <[email protected]>
Date:   Fri Jun 19 18:21:14 2026 +0000

    gcc/cp-tree: require that temp_override deduces on first constructor arg
    
    This helps force a conversion from the second argument into whatever
    type the variable truly is.
    
    This change ended up being unnecessary, but it is probably useful for
    others anyway.
    
    gcc/cp/ChangeLog:
    
            * cp-tree.h (temp_override): In provided-value constructor,
            don't deduce based on provided value.

Diff:
---
 gcc/cp/cp-tree.h | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index a3be24b4fb54..8dac8c98b7a3 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -2256,6 +2256,17 @@ public:
   }
 };
 
+/* Wrapping a template parameter in type_identity_t hides it from template
+   argument deduction.  */
+#if __cpp_lib_type_identity
+using std::type_identity_t;
+#else
+template <typename T>
+struct type_identity { typedef T type; };
+template <typename T>
+using type_identity_t = typename type_identity<T>::type;
+#endif
+
 /* RAII sentinel that saves the value of a variable, optionally
    overrides it right away, and restores its value when the sentinel
    id destructed.  */
@@ -2266,8 +2277,8 @@ class temp_override
   T& overridden_variable;
   T saved_value;
 public:
-  temp_override(T& var) : overridden_variable (var), saved_value (var) {}
-  temp_override(T& var, T overrider)
+  temp_override (T& var) : overridden_variable (var), saved_value (var) {}
+  temp_override (T& var, type_identity_t<T> overrider)
     : overridden_variable (var), saved_value (var)
   {
     overridden_variable = overrider;
@@ -2275,17 +2286,6 @@ public:
   ~temp_override() { overridden_variable = saved_value; }
 };
 
-/* Wrapping a template parameter in type_identity_t hides it from template
-   argument deduction.  */
-#if __cpp_lib_type_identity
-using std::type_identity_t;
-#else
-template <typename T>
-struct type_identity { typedef T type; };
-template <typename T>
-using type_identity_t = typename type_identity<T>::type;
-#endif
-
 /* Object generator function for temp_override, so you don't need to write the
    type of the object as a template argument.