PR c++/90538 - multiple expansions of capture packs

Previously, with init-capture the type of the closure field was a
DECLTYPE_TYPE of the initializer.  But since each time we tsubst a lambda we
get a different lambda, that meant that if the initializer is a lambda, we'd
end up with different closure types in the field and initializer after
substitution (PR 87322).  We dealt with this by remembering the lambda
instantiation within each pack expansion element, using
local_specialization_stack to separate the elements.  But that broke this
testcase, because it lost lambda capture proxies that also use
local_specializations.

So, this patch removes the local_specializations changes from that patch and
fixes 87322 differently, by giving init-capture fields 'auto' type and doing
deduction later.  There's a bit of a kludge to get the right number of
fields by pretending that 'auto...' uses the parameter packs from the
initializer, but it does the trick.

	* cp-tree.h (DECLTYPE_FOR_INIT_CAPTURE): Remove.
	* lambda.c (add_capture): Copy parameter packs from init.
	(lambda_capture_field_type): Always use auto for init-capture.
	* pt.c (uses_parameter_packs): Return tree.
	(tsubst) [DECLTYPE_TYPE]: Remove init-capture handling.
	(gen_elem_of_pack_expansion_instantiation): Don't push
	local_specialization_stack.
	(prepend_one_capture): New.
	(tsubst_lambda_expr): Use it.  Don't touch local_specializations.
	(do_auto_deduction): Avoid redundant error.

From-SVN: r273944

gcc/cp/ChangeLog

@@ -1,5 +1,17 @@
 2019-07-31  Jason Merrill  <jason@redhat.com>
 
+	PR c++/90538 - multiple expansions of capture packs
+	* cp-tree.h (DECLTYPE_FOR_INIT_CAPTURE): Remove.
+	* lambda.c (add_capture): Copy parameter packs from init.
+	(lambda_capture_field_type): Always use auto for init-capture.
+	* pt.c (uses_parameter_packs): Return tree.
+	(tsubst) [DECLTYPE_TYPE]: Remove init-capture handling.
+	(gen_elem_of_pack_expansion_instantiation): Don't push
+	local_specialization_stack.
+	(prepend_one_capture): New.
+	(tsubst_lambda_expr): Use it.  Don't touch local_specializations.
+	(do_auto_deduction): Avoid redundant error.
+
 	Fix copy_node of TEMPLATE_INFO.
 	* cp-tree.h (struct tree_template_info): Use tree_base instead of
 	tree_common.  Add tmpl and args fields.

gcc/cp/cp-tree.h

@@ -423,7 +423,6 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
       LAMBDA_EXPR_MUTABLE_P (in LAMBDA_EXPR)
       DECL_FINAL_P (in FUNCTION_DECL)
       QUALIFIED_NAME_IS_TEMPLATE (in SCOPE_REF)
-      DECLTYPE_FOR_INIT_CAPTURE (in DECLTYPE_TYPE)
       CONSTRUCTOR_IS_DEPENDENT (in CONSTRUCTOR)
       TINFO_USED_TEMPLATE_ID (in TEMPLATE_INFO)
       PACK_EXPANSION_SIZEOF_P (in *_PACK_EXPANSION)
@@ -4484,12 +4483,10 @@ more_aggr_init_expr_args_p (const aggr_init_expr_arg_iterator *iter)
   (DECLTYPE_TYPE_CHECK (NODE))->type_common.string_flag
 
 /* These flags indicate that we want different semantics from normal
-   decltype: lambda capture just drops references, init capture
-   uses auto semantics, lambda proxies look through implicit dereference.  */
+   decltype: lambda capture just drops references,
+   lambda proxies look through implicit dereference.  */
 #define DECLTYPE_FOR_LAMBDA_CAPTURE(NODE) \
   TREE_LANG_FLAG_0 (DECLTYPE_TYPE_CHECK (NODE))
-#define DECLTYPE_FOR_INIT_CAPTURE(NODE) \
-  TREE_LANG_FLAG_1 (DECLTYPE_TYPE_CHECK (NODE))
 #define DECLTYPE_FOR_LAMBDA_PROXY(NODE) \
   TREE_LANG_FLAG_2 (DECLTYPE_TYPE_CHECK (NODE))
 #define DECLTYPE_FOR_REF_CAPTURE(NODE) \
@@ -6794,7 +6791,7 @@ extern bool maybe_instantiate_noexcept		(tree, tsubst_flags_t = tf_warning_or_er
 extern tree instantiate_decl			(tree, bool, bool);
 extern int comp_template_parms			(const_tree, const_tree);
 extern bool builtin_pack_fn_p			(tree);
-extern bool uses_parameter_packs                (tree);
+extern tree uses_parameter_packs                (tree);
 extern bool template_parameter_pack_p           (const_tree);
 extern bool function_parameter_pack_p		(const_tree);
 extern bool function_parameter_expanded_from_pack_p (tree, tree);

gcc/cp/lambda.c

@@ -213,16 +213,7 @@ lambda_capture_field_type (tree expr, bool explicit_init_p,
   tree type;
   bool is_this = is_this_parameter (tree_strip_nop_conversions (expr));
 
-  if (!is_this && type_dependent_expression_p (expr))
-    {
-      type = cxx_make_type (DECLTYPE_TYPE);
-      DECLTYPE_TYPE_EXPR (type) = expr;
-      DECLTYPE_FOR_LAMBDA_CAPTURE (type) = true;
-      DECLTYPE_FOR_INIT_CAPTURE (type) = explicit_init_p;
-      DECLTYPE_FOR_REF_CAPTURE (type) = by_reference_p;
-      SET_TYPE_STRUCTURAL_EQUALITY (type);
-    }
-  else if (!is_this && explicit_init_p)
+  if (!is_this && explicit_init_p)
     {
       tree auto_node = make_auto ();
       
@@ -233,6 +224,14 @@ lambda_capture_field_type (tree expr, bool explicit_init_p,
 	type = build_reference_type (type);
       type = do_auto_deduction (type, expr, auto_node);
     }
+  else if (!is_this && type_dependent_expression_p (expr))
+    {
+      type = cxx_make_type (DECLTYPE_TYPE);
+      DECLTYPE_TYPE_EXPR (type) = expr;
+      DECLTYPE_FOR_LAMBDA_CAPTURE (type) = true;
+      DECLTYPE_FOR_REF_CAPTURE (type) = by_reference_p;
+      SET_TYPE_STRUCTURAL_EQUALITY (type);
+    }
   else
     {
       type = non_reference (unlowered_expr_type (expr));
@@ -594,7 +593,16 @@ add_capture (tree lambda, tree id, tree orig_init, bool by_reference_p,
   name = get_identifier (buf);
 
   if (variadic)
-    type = make_pack_expansion (type);
+    {
+      type = make_pack_expansion (type);
+      if (explicit_init_p)
+	/* With an explicit initializer 'type' is auto, which isn't really a
+	   parameter pack in this context.  We will want as many fields as we
+	   have elements in the expansion of the initializer, so use its packs
+	   instead.  */
+	PACK_EXPANSION_PARAMETER_PACKS (type)
+	  = uses_parameter_packs (initializer);
+    }
 
   /* Make member variable.  */
   member = build_decl (input_location, FIELD_DECL, name, type);

gcc/cp/pt.c

@@ -3872,7 +3872,7 @@ find_parameter_packs_r (tree *tp, int *walk_subtrees, void* data)
 }
 
 /* Determines if the expression or type T uses any parameter packs.  */
-bool
+tree
 uses_parameter_packs (tree t)
 {
   tree parameter_packs = NULL_TREE;
@@ -3882,7 +3882,7 @@ uses_parameter_packs (tree t)
   ppd.type_pack_expansion_p = false;
   cp_walk_tree (&t, &find_parameter_packs_r, &ppd, ppd.visited);
   delete ppd.visited;
-  return parameter_packs != NULL_TREE;
+  return parameter_packs;
 }
 
 /* Turn ARG, which may be an expression, type, or a TREE_LIST
@@ -11764,10 +11764,6 @@ gen_elem_of_pack_expansion_instantiation (tree pattern,
       ARGUMENT_PACK_SELECT_INDEX (aps) = index;
     }
 
-  // Any local specialization bindings arising from this substitution
-  // cannot be reused for a different INDEX.
-  local_specialization_stack lss (lss_copy);
-
   /* Substitute into the PATTERN with the (possibly altered)
      arguments.  */
   if (pattern == in_decl)
@@ -15139,24 +15135,12 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 				      /*function_p*/false,
 				      /*integral_constant_expression*/false);
 
-	if (DECLTYPE_FOR_INIT_CAPTURE (t))
-	  {
-	    if (type == NULL_TREE)
-	      {
-		if (complain & tf_error)
-		  error ("empty initializer in lambda init-capture");
-		type = error_mark_node;
-	      }
-	    else if (TREE_CODE (type) == TREE_LIST)
-	      type = build_x_compound_expr_from_list (type, ELK_INIT, complain);
-	  }
-
 	--cp_unevaluated_operand;
 	--c_inhibit_evaluation_warnings;
 
 	if (DECLTYPE_FOR_LAMBDA_CAPTURE (t))
 	  type = lambda_capture_field_type (type,
-					    DECLTYPE_FOR_INIT_CAPTURE (t),
+					    false /*explicit_init*/,
 					    DECLTYPE_FOR_REF_CAPTURE (t));
 	else if (DECLTYPE_FOR_LAMBDA_PROXY (t))
 	  type = lambda_proxy_type (type);
@@ -18023,6 +18007,33 @@ tsubst_non_call_postfix_expression (tree t, tree args,
   return t;
 }
 
+/* Subroutine of tsubst_lambda_expr: add the FIELD/INIT capture pair to the
+   LAMBDA_EXPR_CAPTURE_LIST passed in LIST.  Do deduction for a previously
+   dependent init-capture.  */
+
+static void
+prepend_one_capture (tree field, tree init, tree &list,
+		     tsubst_flags_t complain)
+{
+  if (tree auto_node = type_uses_auto (TREE_TYPE (field)))
+    {
+      tree type = NULL_TREE;
+      if (!init)
+	{
+	  if (complain & tf_error)
+	    error ("empty initializer in lambda init-capture");
+	  init = error_mark_node;
+	}
+      else if (TREE_CODE (init) == TREE_LIST)
+	init = build_x_compound_expr_from_list (init, ELK_INIT, complain);
+      if (!type)
+	type = do_auto_deduction (TREE_TYPE (field), init, auto_node, complain);
+      TREE_TYPE (field) = type;
+      cp_apply_type_quals_to_decl (cp_type_quals (type), field);
+    }
+  list = tree_cons (field, init, list);
+}
+
 /* T is a LAMBDA_EXPR.  Generate a new LAMBDA_EXPR for the current
    instantiation context.  Instantiating a pack expansion containing a lambda
    might result in multiple lambdas all based on the same lambda in the
@@ -18034,17 +18045,8 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
   tree oldfn = lambda_function (t);
   in_decl = oldfn;
 
-  /* If we have already specialized this lambda expr, reuse it.  See
-     PR c++/87322.  */
-  if (local_specializations)
-    if (tree r = retrieve_local_specialization (t))
-      return r;
-
   tree r = build_lambda_expr ();
 
-  if (local_specializations)
-    register_local_specialization (r, t);
-
   LAMBDA_EXPR_LOCATION (r)
     = LAMBDA_EXPR_LOCATION (t);
   LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (r)
@@ -18097,15 +18099,15 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	  gcc_assert (TREE_CODE (init) == TREE_VEC
 		      && TREE_VEC_LENGTH (init) == len);
 	  for (int i = 0; i < len; ++i)
-	    LAMBDA_EXPR_CAPTURE_LIST (r)
-	      = tree_cons (TREE_VEC_ELT (field, i),
-			   TREE_VEC_ELT (init, i),
-			   LAMBDA_EXPR_CAPTURE_LIST (r));
+	    prepend_one_capture (TREE_VEC_ELT (field, i),
+				 TREE_VEC_ELT (init, i),
+				 LAMBDA_EXPR_CAPTURE_LIST (r),
+				 complain);
 	}
       else
 	{
-	  LAMBDA_EXPR_CAPTURE_LIST (r)
-	    = tree_cons (field, init, LAMBDA_EXPR_CAPTURE_LIST (r));
+	  prepend_one_capture (field, init, LAMBDA_EXPR_CAPTURE_LIST (r),
+			       complain);
 
 	  if (id_equal (DECL_NAME (field), "__this"))
 	    LAMBDA_EXPR_THIS_CAPTURE (r) = field;
@@ -27602,6 +27604,9 @@ do_auto_deduction (tree type, tree init, tree auto_node,
     }
   else
     {
+      if (error_operand_p (init))
+	return error_mark_node;
+
       tree parms = build_tree_list (NULL_TREE, type);
       tree tparms;
 

gcc/testsuite/g++.dg/cpp0x/lambda/lambda-variadic9.C

@@ -0,0 +1,16 @@
+// PR c++/90538
+// { dg-do compile { target c++11 } }
+
+template <class... Ts>
+void f(Ts... ts)
+{
+  [=]{
+    f(ts...);
+    f(ts...);
+  }();
+}
+
+void g()
+{
+  f(1);
+}

gcc/testsuite/g++.dg/cpp0x/range-for19.C

@@ -5,6 +5,6 @@
 int main()
 {
   auto a;        // { dg-error "no initializer" }
-  for(auto i: a) // { dg-error "deduce" }
+  for(auto i: a)
     ;
 }

gcc/testsuite/g++.dg/cpp1y/lambda-init16.C

@@ -3,7 +3,7 @@
 
 template < class T = int > void f (T)
 {
-  auto g = [&a = f] () {};  // { dg-error "invalid initialization" }
+  auto g = [&a = f] () {};  // { dg-error "auto" }
 }
 
 int main ()