[PATCH] c++: CONSTRUCTORs are non-deduced contexts [PR104291]

[PATCH] c++: CONSTRUCTORs are non-deduced contexts [PR104291]

[Patrick Palka]

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

	PR c++/104291

gcc/cp/ChangeLog:

	* pt.cc (for_each_template_parm_r) <case CONSTRUCTOR>: Don't
	walk subtrees if !include_nondeduced_p.  Simplify given that
	cp_walk_subtrees already walks TYPE_PTRMEMFUNC_FN_TYPE_RAW.

gcc/testsuite/ChangeLog:

	* g++.dg/template/partial20.C: New test.
---
 gcc/cp/pt.cc                              | 7 +------
 gcc/testsuite/g++.dg/template/partial20.C | 7 +++++++
 2 files changed, 8 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/partial20.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 2f82b167853..feee629f1dd 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -10525,12 +10525,6 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d)
       *walk_subtrees = 0;
       break;
 
-    case CONSTRUCTOR:
-      if (TREE_TYPE (t) && TYPE_PTRMEMFUNC_P (TREE_TYPE (t))
-	  && pfd->include_nondeduced_p)
-	WALK_SUBTREE (TYPE_PTRMEMFUNC_FN_TYPE (TREE_TYPE (t)));
-      break;
-
     case INDIRECT_REF:
     case COMPONENT_REF:
       /* If there's no type, then this thing must be some expression
@@ -10539,6 +10533,7 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d)
 	return error_mark_node;
       break;
 
+    case CONSTRUCTOR:
     case TRAIT_EXPR:
     case PLUS_EXPR:
     case MULT_EXPR:
diff --git a/gcc/testsuite/g++.dg/template/partial20.C b/gcc/testsuite/g++.dg/template/partial20.C
new file mode 100644
index 00000000000..161d796b1c2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/partial20.C
@@ -0,0 +1,7 @@
+// PR c++/104291
+// { dg-do compile { target c++20 } }
+
+struct A { int x; };
+
+template<auto> struct B;
+template<int x> struct B<A{x}> { }; // { dg-error "not deducible" }
-- 
2.35.0

Re: [PATCH] c++: CONSTRUCTORs are non-deduced contexts [PR104291]

[Jason Merrill]

On 1/31/22 12:27, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
> 
> 	PR c++/104291
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (for_each_template_parm_r) <case CONSTRUCTOR>: Don't
> 	walk subtrees if !include_nondeduced_p.  Simplify given that
> 	cp_walk_subtrees already walks TYPE_PTRMEMFUNC_FN_TYPE_RAW.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/template/partial20.C: New test.
> ---
>   gcc/cp/pt.cc                              | 7 +------
>   gcc/testsuite/g++.dg/template/partial20.C | 7 +++++++
>   2 files changed, 8 insertions(+), 6 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/template/partial20.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 2f82b167853..feee629f1dd 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -10525,12 +10525,6 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d)
>         *walk_subtrees = 0;
>         break;
>   
> -    case CONSTRUCTOR:
> -      if (TREE_TYPE (t) && TYPE_PTRMEMFUNC_P (TREE_TYPE (t))
> -	  && pfd->include_nondeduced_p)
> -	WALK_SUBTREE (TYPE_PTRMEMFUNC_FN_TYPE (TREE_TYPE (t)));
> -      break;
>
>       case INDIRECT_REF:
>       case COMPONENT_REF:
>         /* If there's no type, then this thing must be some expression
> @@ -10539,6 +10533,7 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d)
>   	return error_mark_node;
>         break;
>   
> +    case CONSTRUCTOR:
>       case TRAIT_EXPR:
>       case PLUS_EXPR:
>       case MULT_EXPR:

OK, thanks.

Looking at this area, I'm puzzled by the ancient (!fn) code.  AFAICT 
nothing calls for_each_template_parm with null FN anymore; it used to be 
used by uses_template_parms, until r76647 in 2004.  I'll play with 
cleaning that up.

> diff --git a/gcc/testsuite/g++.dg/template/partial20.C b/gcc/testsuite/g++.dg/template/partial20.C
> new file mode 100644
> index 00000000000..161d796b1c2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/partial20.C
> @@ -0,0 +1,7 @@
> +// PR c++/104291
> +// { dg-do compile { target c++20 } }
> +
> +struct A { int x; };
> +
> +template<auto> struct B;
> +template<int x> struct B<A{x}> { }; // { dg-error "not deducible" }