On Wed, 2 Feb 2022, Patrick Palka wrote:
> Here we're crashing during satisfaction of the lambda's placeholder type
> constraints because the constraints depend on the template arguments
> from the enclosing scope, which aren't a part of the lambda's
> DECL_TI_ARGS. So when inside a lambda, do_auto_deduction needs to add
> the "regenerating" template arguments to the set of outer template
> arguments, like we already do in satisfy_declaration_constraints.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk and perhaps 11?
>
> PR c++/103706
>
> gcc/cp/ChangeLog:
>
> * constraint.cc (satisfy_declaration_constraints): Use
> lambda_regenerating_args instead.
> * cp-tree.h (lambda_regenerating_args): Declare.
> * pt.cc (add_to_template_args): Handle NULL_TREE extra_args
> gracefully.
> (lambda_regenerating_args): Define, split out from
> satisfy_declaration_constraints.
> (do_auto_deduction): Use lambda_regenerating_args to obtain the
> full set of outer template arguments when checking the
> constraint on a placeholder type within a lambda.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/concepts-lambda18.C: New test.
> ---
> gcc/cp/constraint.cc | 9 +----
> gcc/cp/cp-tree.h | 1 +
> gcc/cp/pt.cc | 37 ++++++++++++++++---
> .../g++.dg/cpp2a/concepts-lambda18.C | 14 +++++++
> 4 files changed, 48 insertions(+), 13 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
>
> diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> index cc4df4216ef..c41ee02b910 100644
> --- a/gcc/cp/constraint.cc
> +++ b/gcc/cp/constraint.cc
> @@ -3148,18 +3148,13 @@ satisfy_declaration_constraints (tree t, sat_info
> info)
> args = add_outermost_template_args (args, inh_ctor_targs);
> }
>
> - if (regenerated_lambda_fn_p (t))
> + if (LAMBDA_FUNCTION_P (t))
> {
> /* The TI_ARGS of a regenerated lambda contains only the innermost
> set of template arguments. Augment this with the outer template
> arguments that were used to regenerate the lambda. */
> gcc_assert (!args || TMPL_ARGS_DEPTH (args) == 1);
> - tree lambda = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (t));
> - tree outer_args = TI_ARGS (LAMBDA_EXPR_REGEN_INFO (lambda));
> - if (args)
> - args = add_to_template_args (outer_args, args);
> - else
> - args = outer_args;
> + args = add_to_template_args (lambda_regenerating_args (t), args);
> }
>
> /* If any arguments depend on template parameters, we can't
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index b9eb71fbc3a..7a7fe5ba599 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -7715,6 +7715,7 @@ extern void finish_lambda_scope (void);
> extern tree start_lambda_function (tree fn, tree lambda_expr);
> extern void finish_lambda_function (tree body);
> extern bool regenerated_lambda_fn_p (tree);
> +extern tree lambda_regenerating_args (tree);
> extern tree most_general_lambda (tree);
> extern tree finish_omp_target (location_t, tree,
> tree, bool);
> extern void finish_omp_target_clauses (location_t, tree, tree
> *);
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 6e129da1d05..c919d2de68f 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -573,6 +573,9 @@ add_to_template_args (tree args, tree extra_args)
> if (args == NULL_TREE || extra_args == error_mark_node)
> return extra_args;
>
> + if (extra_args == NULL_TREE)
> + return args;
> +
Whoops, this last-minute change to add_to_template_args turned out to
be a bad idea as some callers apparently rely on add_to_template_args
treating NULL_TREE extra_args as a depth 1 targ vector (whereas for
the calls in satisfy_declaration_constraints and do_auto_deduction we
want NULL_TREE extra_args to be treated as a depth 0 targ vector).
Please consider the below patch instead, which doesn't attempt to change
the behavior of add_to_template_args:
-- >8 --
Subject: [PATCH] c++: constrained auto in lambda using outer tparms [PR103706]
Here we're crashing during satisfaction of the lambda's placeholder type
constraints because the constraints depend on the template arguments
from the enclosing scope, which aren't part of the lambda's DECL_TI_ARGS.
So when inside a lambda, do_auto_deduction needs to add its
"regenerating" template arguments to the set of outer template
arguments, like we already do in satisfy_declaration_constraints.
PR c++/103706
gcc/cp/ChangeLog:
* constraint.cc (satisfy_declaration_constraints): Use
lambda_regenerating_args instead.
* cp-tree.h (lambda_regenerating_args): Declare.
* pt.cc (lambda_regenerating_args): Define, split out from
satisfy_declaration_constraints.
(do_auto_deduction): Use lambda_regenerating_args to obtain the
full set of outer template arguments for satisfaction.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-lambda18.C: New test.
---
gcc/cp/constraint.cc | 9 ++---
gcc/cp/cp-tree.h | 1 +
gcc/cp/pt.cc | 39 ++++++++++++++++---
.../g++.dg/cpp2a/concepts-lambda18.C | 14 +++++++
4 files changed, 52 insertions(+), 11 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index cc4df4216ef..c0ebe63a0a2 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3148,18 +3148,17 @@ satisfy_declaration_constraints (tree t, sat_info info)
args = add_outermost_template_args (args, inh_ctor_targs);
}
- if (regenerated_lambda_fn_p (t))
+ if (LAMBDA_FUNCTION_P (t))
{
/* The TI_ARGS of a regenerated lambda contains only the innermost
set of template arguments. Augment this with the outer template
arguments that were used to regenerate the lambda. */
gcc_assert (!args || TMPL_ARGS_DEPTH (args) == 1);
- tree lambda = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (t));
- tree outer_args = TI_ARGS (LAMBDA_EXPR_REGEN_INFO (lambda));
+ tree regen_args = lambda_regenerating_args (t);
if (args)
- args = add_to_template_args (outer_args, args);
+ args = add_to_template_args (regen_args, args);
else
- args = outer_args;
+ args = regen_args;
}
/* If any arguments depend on template parameters, we can't
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index b9eb71fbc3a..7a7fe5ba599 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7715,6 +7715,7 @@ extern void finish_lambda_scope (void);
extern tree start_lambda_function (tree fn, tree lambda_expr);
extern void finish_lambda_function (tree body);
extern bool regenerated_lambda_fn_p (tree);
+extern tree lambda_regenerating_args (tree);
extern tree most_general_lambda (tree);
extern tree finish_omp_target (location_t, tree, tree, bool);
extern void finish_omp_target_clauses (location_t, tree, tree *);
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 6e129da1d05..46754c611e7 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -14442,6 +14442,21 @@ most_general_lambda (tree t)
return t;
}
+/* Return the set of template arguments used to regenerate the lambda T
+ from its most general lambda. */
+
+tree
+lambda_regenerating_args (tree t)
+{
+ if (LAMBDA_FUNCTION_P (t))
+ t = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (t));
+ gcc_assert (TREE_CODE (t) == LAMBDA_EXPR);
+ if (tree ti = LAMBDA_EXPR_REGEN_INFO (t))
+ return TI_ARGS (ti);
+ else
+ return NULL_TREE;
+}
+
/* We're instantiating a variable from template function TCTX. Return the
corresponding current enclosing scope. We can match them up using
DECL_SOURCE_LOCATION because lambdas only ever have one source location, and
@@ -30100,12 +30115,24 @@ do_auto_deduction (tree type, tree init, tree
auto_node,
return type;
}
- if ((context == adc_return_type
- || context == adc_variable_type
- || context == adc_decomp_type)
- && current_function_decl
- && DECL_TEMPLATE_INFO (current_function_decl))
- outer_targs = DECL_TI_ARGS (current_function_decl);
+ if (context == adc_return_type
+ || context == adc_variable_type
+ || context == adc_decomp_type)
+ if (tree fn = current_function_decl)
+ if (DECL_TEMPLATE_INFO (fn) || LAMBDA_FUNCTION_P (fn))
+ {
+ outer_targs
+ = DECL_TEMPLATE_INFO (fn) ? DECL_TI_ARGS (fn) : NULL_TREE;
+ if (LAMBDA_FUNCTION_P (fn))
+ {
+ /* As in satisfy_declaration_constraints. */
+ tree regen_args = lambda_regenerating_args (fn);
+ if (outer_targs)
+ outer_targs = add_to_template_args (regen_args,
outer_targs);
+ else
+ outer_targs = regen_args;
+ }
+ }
tree full_targs = add_to_template_args (outer_targs, targs);
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
new file mode 100644
index 00000000000..f1058daf317
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
@@ -0,0 +1,14 @@
+// PR c++/103706
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept C = __is_same(U, int);
+
+template<class T> void f() {
+ []() -> C<T> auto {
+ C<T> auto x = T(); // { dg-error "constraints" }
+ return T(); // { dg-error "constraints" }
+ }();
+}
+
+template void f<int>(); // { dg-bogus "" }
+template void f<char>(); // { dg-message "required from here" }
--
2.35.0
