c++: nested aggregate/alias CTAD fixes

  Bootstrapped and regtested on x86-64-pc-linux-gnu, does this look
OK for trunk and perhaps 14?

-- >8 --

During maybe_aggr_guide with a nested class template and paren init,
like with list init we need to consider the generic template type rather
than the partially instantiated type since only the former has
TYPE_FIELDS.  And in turn we need to partially substitute PARMs in the
paren init case as well.  As a drive-by improvement it seems better to
use outer_template_args instead of DECL_TI_ARGS during this partial
substitution so that we lower instead of substitute the innermost
generic template arguments, which is generally more robust.

And during alias_ctad_tweaks with a nested class template, even though
the guides may be already partially instantiated we still need to
use the full set of arguments, not just the innermost, when substituting
its constraints.

	PR c++/114974
	PR c++/114901
	PR c++/114903

gcc/cp/ChangeLog:

	* pt.cc (maybe_aggr_guide): Fix obtaining TYPE_FIELDS in
	the paren init case.  Hoist out partial substitution logic
	to apply to the paren init case as well.
	(alias_ctad_tweaks): Substitute constraints using the full
	set of template arguments.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/class-deduction-aggr14.C: New test.
	* g++.dg/cpp2a/class-deduction-alias20.C: New test.
	* g++.dg/cpp2a/class-deduction-alias21.C: New test.
---
 gcc/cp/pt.cc                                  | 39 +++++++++++--------
 .../g++.dg/cpp2a/class-deduction-aggr14.C     | 11 ++++++
 .../g++.dg/cpp2a/class-deduction-alias20.C    | 22 +++++++++++
 .../g++.dg/cpp2a/class-deduction-alias21.C    | 38 ++++++++++++++++++
 4 files changed, 93 insertions(+), 17 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C
  

On Wed, 8 May 2024, Patrick Palka wrote:

> Bootstrapped and regtested on x86-64-pc-linux-gnu, does this look
> OK for trunk and perhaps 14?
> 
> -- >8 --
> 
> During maybe_aggr_guide with a nested class template and paren init,
> like with list init we need to consider the generic template type rather
> than the partially instantiated type since only the former has
> TYPE_FIELDS.  And in turn we need to partially substitute PARMs in the
> paren init case as well.  As a drive-by improvement it seems better to
> use outer_template_args instead of DECL_TI_ARGS during this partial
> substitution so that we lower instead of substitute the innermost
> generic template arguments, which is generally more robust.

... lower instead of substitute the innermost _template parameters_, rather

> 
> And during alias_ctad_tweaks with a nested class template, even though
> the guides may be already partially instantiated we still need to
> use the full set of arguments, not just the innermost, when substituting
> its constraints.
> 
> 	PR c++/114974
> 	PR c++/114901
> 	PR c++/114903
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (maybe_aggr_guide): Fix obtaining TYPE_FIELDS in
> 	the paren init case.  Hoist out partial substitution logic
> 	to apply to the paren init case as well.
> 	(alias_ctad_tweaks): Substitute constraints using the full
> 	set of template arguments.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/class-deduction-aggr14.C: New test.
> 	* g++.dg/cpp2a/class-deduction-alias20.C: New test.
> 	* g++.dg/cpp2a/class-deduction-alias21.C: New test.
> ---
>  gcc/cp/pt.cc                                  | 39 +++++++++++--------
>  .../g++.dg/cpp2a/class-deduction-aggr14.C     | 11 ++++++
>  .../g++.dg/cpp2a/class-deduction-alias20.C    | 22 +++++++++++
>  .../g++.dg/cpp2a/class-deduction-alias21.C    | 38 ++++++++++++++++++
>  4 files changed, 93 insertions(+), 17 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C
>  create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C
>  create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 1816bfd1f40..f3d52acaaac 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -30192,26 +30192,11 @@ maybe_aggr_guide (tree tmpl, tree init, vec<tree,va_gc> *args)
>        if (init == error_mark_node)
>  	return NULL_TREE;
>        parms = collect_ctor_idx_types (init, parms);
> -      /* If we're creating a deduction guide for a member class template,
> -	 we've used the original template pattern type for the reshape_init
> -	 above; this is done because we want PARMS to be a template parameter
> -	 type, something that can be deduced when used as a function template
> -	 parameter.  At this point the outer class template has already been
> -	 partially instantiated (we deferred the deduction until the enclosing
> -	 scope is non-dependent).  Therefore we have to partially instantiate
> -	 PARMS, so that its template level is properly reduced and we don't get
> -	 mismatches when deducing types using the guide with PARMS.  */
> -      if (member_template_p)
> -	{
> -	  ++processing_template_decl;
> -	  parms = tsubst (parms, DECL_TI_ARGS (tmpl), complain, init);
> -	  --processing_template_decl;
> -	}
>      }
>    else if (TREE_CODE (init) == TREE_LIST)
>      {
>        int len = list_length (init);
> -      for (tree field = TYPE_FIELDS (type);
> +      for (tree field = TYPE_FIELDS (template_type);
>  	   len;
>  	   --len, field = DECL_CHAIN (field))
>  	{
> @@ -30226,6 +30211,22 @@ maybe_aggr_guide (tree tmpl, tree init, vec<tree,va_gc> *args)
>      /* Aggregate initialization doesn't apply to an initializer expression.  */
>      return NULL_TREE;
>  
> +  /* If we're creating a deduction guide for a member class template,
> +     we've used the original template pattern type for the reshape_init
> +     above; this is done because we want PARMS to be a template parameter
> +     type, something that can be deduced when used as a function template
> +     parameter.  At this point the outer class template has already been
> +     partially instantiated (we deferred the deduction until the enclosing
> +     scope is non-dependent).  Therefore we have to partially instantiate
> +     PARMS, so that its template level is properly reduced and we don't get
> +     mismatches when deducing types using the guide with PARMS.  */
> +  if (member_template_p)
> +    {
> +      ++processing_template_decl;
> +      parms = tsubst (parms, outer_template_args (tmpl), complain, init);
> +      --processing_template_decl;
> +    }
> +
>    if (parms)
>      {
>        tree last = parms;
> @@ -30417,7 +30418,11 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
>  	  /* Substitute the associated constraints.  */
>  	  tree ci = get_constraints (f);
>  	  if (ci)
> -	    ci = tsubst_constraint_info (ci, targs, complain, in_decl);
> +	    {
> +	      if (tree outer_targs = outer_template_args (f))
> +		ci = tsubst_constraint_info (ci, outer_targs, complain, in_decl);
> +	      ci = tsubst_constraint_info (ci, targs, complain, in_decl);
> +	    }
>  	  if (ci == error_mark_node)
>  	    continue;
>  
> diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C
> new file mode 100644
> index 00000000000..68786652502
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C
> @@ -0,0 +1,11 @@
> +// PR c++/114974
> +// { dg-do compile { target c++20 } }
> +
> +template<typename T1>
> +struct A {
> +  template<typename T2>
> +  struct B { T2 t; };
> +};
> +
> +A<int>::B x{2}; // OK
> +A<int>::B y(2); // previously rejected
> diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C
> new file mode 100644
> index 00000000000..8cc56d91e37
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C
> @@ -0,0 +1,22 @@
> +// PR c++/114901
> +// { dg-do compile { target c++20 } }
> +
> +template <class D>
> +constexpr bool C = sizeof(D);
> +
> +template <typename U>
> +struct T {
> +  template<typename V, typename N>
> +  struct Foo {
> +    Foo(V, N);
> +  };
> +
> +  template<typename X, typename N>
> +  requires (C<N>) // removes the require-clause will make the crash disappear
> +  Foo(X, N) -> Foo<X, N>;
> +
> +  template <typename Y, typename Y2, int N = sizeof(Y2)>
> +  using AFoo = Foo<decltype(N), Y2>;
> +};
> +
> +T<double>::AFoo s{1, 2}; // { dg-error "deduction|no match" }
> diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C
> new file mode 100644
> index 00000000000..c39a0f9f141
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C
> @@ -0,0 +1,38 @@
> +// PR c++/114903
> +// { dg-do compile { target c++20 } }
> +
> +template <typename T>
> +struct Key {
> +  Key(int);
> +};
> +
> +class Forward {};
> +
> +template <typename T>
> +constexpr bool C = __is_same(T, Forward);
> +
> +template <typename Z>
> +struct Outer {
> +  template <typename U>
> +  struct Foo {
> +    Foo(U);
> +    U u;
> +  };
> +
> +  template <typename V>
> +    requires(C<Z>)
> +  Foo(V) -> Foo<int>;
> +};
> +
> +template <typename Y>
> +struct T {
> +  template <typename Y2>
> +  struct T2 {
> +    template <typename K>
> +    using AFoo = Outer<Y2>::template Foo<K>;
> +  };
> +};
> +
> +T<Forward>::T2<Forward>::AFoo a(1.0);
> +using type = decltype(a);
> +using type = Outer<Forward>::Foo<int>;
> -- 
> 2.45.0.31.gd4cc1ec35f
> 
>
  

On 5/8/24 13:49, Patrick Palka wrote:
> Bootstrapped and regtested on x86-64-pc-linux-gnu, does this look
> OK for trunk and perhaps 14?

OK for both.

> -- >8 --
> 
> During maybe_aggr_guide with a nested class template and paren init,
> like with list init we need to consider the generic template type rather
> than the partially instantiated type since only the former has
> TYPE_FIELDS.  And in turn we need to partially substitute PARMs in the
> paren init case as well.  As a drive-by improvement it seems better to
> use outer_template_args instead of DECL_TI_ARGS during this partial
> substitution so that we lower instead of substitute the innermost
> generic template arguments, which is generally more robust.
> 
> And during alias_ctad_tweaks with a nested class template, even though
> the guides may be already partially instantiated we still need to
> use the full set of arguments, not just the innermost, when substituting
> its constraints.
> 
> 	PR c++/114974
> 	PR c++/114901
> 	PR c++/114903
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (maybe_aggr_guide): Fix obtaining TYPE_FIELDS in
> 	the paren init case.  Hoist out partial substitution logic
> 	to apply to the paren init case as well.
> 	(alias_ctad_tweaks): Substitute constraints using the full
> 	set of template arguments.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/class-deduction-aggr14.C: New test.
> 	* g++.dg/cpp2a/class-deduction-alias20.C: New test.
> 	* g++.dg/cpp2a/class-deduction-alias21.C: New test.
> ---
>   gcc/cp/pt.cc                                  | 39 +++++++++++--------
>   .../g++.dg/cpp2a/class-deduction-aggr14.C     | 11 ++++++
>   .../g++.dg/cpp2a/class-deduction-alias20.C    | 22 +++++++++++
>   .../g++.dg/cpp2a/class-deduction-alias21.C    | 38 ++++++++++++++++++
>   4 files changed, 93 insertions(+), 17 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 1816bfd1f40..f3d52acaaac 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -30192,26 +30192,11 @@ maybe_aggr_guide (tree tmpl, tree init, vec<tree,va_gc> *args)
>         if (init == error_mark_node)
>   	return NULL_TREE;
>         parms = collect_ctor_idx_types (init, parms);
> -      /* If we're creating a deduction guide for a member class template,
> -	 we've used the original template pattern type for the reshape_init
> -	 above; this is done because we want PARMS to be a template parameter
> -	 type, something that can be deduced when used as a function template
> -	 parameter.  At this point the outer class template has already been
> -	 partially instantiated (we deferred the deduction until the enclosing
> -	 scope is non-dependent).  Therefore we have to partially instantiate
> -	 PARMS, so that its template level is properly reduced and we don't get
> -	 mismatches when deducing types using the guide with PARMS.  */
> -      if (member_template_p)
> -	{
> -	  ++processing_template_decl;
> -	  parms = tsubst (parms, DECL_TI_ARGS (tmpl), complain, init);
> -	  --processing_template_decl;
> -	}
>       }
>     else if (TREE_CODE (init) == TREE_LIST)
>       {
>         int len = list_length (init);
> -      for (tree field = TYPE_FIELDS (type);
> +      for (tree field = TYPE_FIELDS (template_type);
>   	   len;
>   	   --len, field = DECL_CHAIN (field))
>   	{
> @@ -30226,6 +30211,22 @@ maybe_aggr_guide (tree tmpl, tree init, vec<tree,va_gc> *args)
>       /* Aggregate initialization doesn't apply to an initializer expression.  */
>       return NULL_TREE;
>   
> +  /* If we're creating a deduction guide for a member class template,
> +     we've used the original template pattern type for the reshape_init
> +     above; this is done because we want PARMS to be a template parameter
> +     type, something that can be deduced when used as a function template
> +     parameter.  At this point the outer class template has already been
> +     partially instantiated (we deferred the deduction until the enclosing
> +     scope is non-dependent).  Therefore we have to partially instantiate
> +     PARMS, so that its template level is properly reduced and we don't get
> +     mismatches when deducing types using the guide with PARMS.  */
> +  if (member_template_p)
> +    {
> +      ++processing_template_decl;
> +      parms = tsubst (parms, outer_template_args (tmpl), complain, init);
> +      --processing_template_decl;
> +    }
> +
>     if (parms)
>       {
>         tree last = parms;
> @@ -30417,7 +30418,11 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
>   	  /* Substitute the associated constraints.  */
>   	  tree ci = get_constraints (f);
>   	  if (ci)
> -	    ci = tsubst_constraint_info (ci, targs, complain, in_decl);
> +	    {
> +	      if (tree outer_targs = outer_template_args (f))
> +		ci = tsubst_constraint_info (ci, outer_targs, complain, in_decl);
> +	      ci = tsubst_constraint_info (ci, targs, complain, in_decl);
> +	    }
>   	  if (ci == error_mark_node)
>   	    continue;
>   
> diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C
> new file mode 100644
> index 00000000000..68786652502
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr14.C
> @@ -0,0 +1,11 @@
> +// PR c++/114974
> +// { dg-do compile { target c++20 } }
> +
> +template<typename T1>
> +struct A {
> +  template<typename T2>
> +  struct B { T2 t; };
> +};
> +
> +A<int>::B x{2}; // OK
> +A<int>::B y(2); // previously rejected
> diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C
> new file mode 100644
> index 00000000000..8cc56d91e37
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias20.C
> @@ -0,0 +1,22 @@
> +// PR c++/114901
> +// { dg-do compile { target c++20 } }
> +
> +template <class D>
> +constexpr bool C = sizeof(D);
> +
> +template <typename U>
> +struct T {
> +  template<typename V, typename N>
> +  struct Foo {
> +    Foo(V, N);
> +  };
> +
> +  template<typename X, typename N>
> +  requires (C<N>) // removes the require-clause will make the crash disappear
> +  Foo(X, N) -> Foo<X, N>;
> +
> +  template <typename Y, typename Y2, int N = sizeof(Y2)>
> +  using AFoo = Foo<decltype(N), Y2>;
> +};
> +
> +T<double>::AFoo s{1, 2}; // { dg-error "deduction|no match" }
> diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C
> new file mode 100644
> index 00000000000..c39a0f9f141
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias21.C
> @@ -0,0 +1,38 @@
> +// PR c++/114903
> +// { dg-do compile { target c++20 } }
> +
> +template <typename T>
> +struct Key {
> +  Key(int);
> +};
> +
> +class Forward {};
> +
> +template <typename T>
> +constexpr bool C = __is_same(T, Forward);
> +
> +template <typename Z>
> +struct Outer {
> +  template <typename U>
> +  struct Foo {
> +    Foo(U);
> +    U u;
> +  };
> +
> +  template <typename V>
> +    requires(C<Z>)
> +  Foo(V) -> Foo<int>;
> +};
> +
> +template <typename Y>
> +struct T {
> +  template <typename Y2>
> +  struct T2 {
> +    template <typename K>
> +    using AFoo = Outer<Y2>::template Foo<K>;
> +  };
> +};
> +
> +T<Forward>::T2<Forward>::AFoo a(1.0);
> +using type = decltype(a);
> +using type = Outer<Forward>::Foo<int>;