[PATCH] c++: alias CTAD inside decltype [PR101233]

[PATCH] c++: alias CTAD inside decltype [PR101233]

[Patrick Palka]

This is the alias CTAD version of the CTAD bug PR93248, and the fix is
the same: clear cp_unevaluated_operand so that the entire chain of
DECL_ARGUMENTS gets substituted.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/11?

	PR c++/101233

gcc/cp/ChangeLog:

	* pt.c (alias_ctad_tweaks): Clear cp_unevaluated_operand for
	substituting DECL_ARGUMENTS.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/class-deduction-alias10.C: New test.
---
 gcc/cp/pt.c                                          | 12 +++++++++---
 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C | 10 ++++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index c7bf7d412ca..bc0a0936579 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -29097,9 +29097,15 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
 	  /* Substitute the deduced arguments plus the rewritten template
 	     parameters into f to get g.  This covers the type, copyness,
 	     guideness, and explicit-specifier.  */
-	  tree g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain);
-	  if (g == error_mark_node)
-	    continue;
+	  tree g;
+	    {
+	      /* Parms are to have DECL_CHAIN tsubsted, which would be skipped
+		 if cp_unevaluated_operand.  */
+	      cp_evaluated ev;
+	      g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain);
+	      if (g == error_mark_node)
+		continue;
+	    }
 	  DECL_USE_TEMPLATE (g) = 0;
 	  fprime = build_template_decl (g, gtparms, false);
 	  DECL_TEMPLATE_RESULT (fprime) = g;
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C
new file mode 100644
index 00000000000..a473fff5dc7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C
@@ -0,0 +1,10 @@
+// PR c++/101233
+// { dg-do compile { target c++20 } }
+
+template<class T, class U>
+struct A { A(T, U); };
+
+template<class T, class U>
+using B = A<U, T>;
+
+using type = decltype(B{0, 0});
-- 
2.32.0.264.g75ae10bc75

Re: [PATCH] c++: alias CTAD inside decltype [PR101233]

[Jason Merrill]

On 7/15/21 12:37 PM, Patrick Palka wrote:
> This is the alias CTAD version of the CTAD bug PR93248, and the fix is
> the same: clear cp_unevaluated_operand so that the entire chain of
> DECL_ARGUMENTS gets substituted.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/11?

OK.

> 	PR c++/101233
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.c (alias_ctad_tweaks): Clear cp_unevaluated_operand for
> 	substituting DECL_ARGUMENTS.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/class-deduction-alias10.C: New test.
> ---
>   gcc/cp/pt.c                                          | 12 +++++++++---
>   gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C | 10 ++++++++++
>   2 files changed, 19 insertions(+), 3 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C
> 
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index c7bf7d412ca..bc0a0936579 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -29097,9 +29097,15 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
>   	  /* Substitute the deduced arguments plus the rewritten template
>   	     parameters into f to get g.  This covers the type, copyness,
>   	     guideness, and explicit-specifier.  */
> -	  tree g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain);
> -	  if (g == error_mark_node)
> -	    continue;
> +	  tree g;
> +	    {
> +	      /* Parms are to have DECL_CHAIN tsubsted, which would be skipped
> +		 if cp_unevaluated_operand.  */
> +	      cp_evaluated ev;
> +	      g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain);
> +	      if (g == error_mark_node)
> +		continue;
> +	    }
>   	  DECL_USE_TEMPLATE (g) = 0;
>   	  fprime = build_template_decl (g, gtparms, false);
>   	  DECL_TEMPLATE_RESULT (fprime) = g;
> diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C
> new file mode 100644
> index 00000000000..a473fff5dc7
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C
> @@ -0,0 +1,10 @@
> +// PR c++/101233
> +// { dg-do compile { target c++20 } }
> +
> +template<class T, class U>
> +struct A { A(T, U); };
> +
> +template<class T, class U>
> +using B = A<U, T>;
> +
> +using type = decltype(B{0, 0});
>