c++: Member initializer list diagnostic locations [PR94024]

This patch preserves the source locations of each node in a member
initializer list so that during processing of the list we can set
input_location appropriately for generally more accurate diagnostic
locations.  Since TREE_LIST nodes are tcc_exceptional, they can't have
source locations, so we instead store the location in a dummy
tcc_expression node within the TREE_TYPE of the list node.

gcc/cp/ChangeLog:

	PR c++/94024
	* init.c (sort_mem_initializers): Preserve TREE_TYPE of the
	member initializer list node.
	(emit_mem_initializers): Set input_location when performing each
	member initialization.
	* parser.c (cp_parser_mem_initializer): Attach the source
	location of this initializer to a dummy EMPTY_CLASS_EXPR
	within the TREE_TYPE of the list node.
	* pt.c (tsubst_initializer_list): Preserve TREE_TYPE of the
	member initializer list node.

gcc/testsuite/ChangeLog:

	PR c++/94024
	* g++.dg/diagnostic/mem-init1.C: New test.

1 files changed, 6 insertions, 0 deletions

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index cb9bd2d..3f08940 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -1151,6 +1151,8 @@ sort_mem_initializers (tree t, tree mem_inits)
 
       /* Record the initialization.  */
       TREE_VALUE (subobject_init) = TREE_VALUE (init);
+      /* Carry over the dummy TREE_TYPE node containing the source location.  */
+      TREE_TYPE (subobject_init) = TREE_TYPE (init);
       next_subobject = subobject_init;
     }
 
@@ -1367,6 +1369,10 @@ emit_mem_initializers (tree mem_inits)
   /* Initialize the data members.  */
   while (mem_inits)
     {
+      /* If this initializer was explicitly provided, then the dummy TREE_TYPE
+	 node contains the source location.  */
+      iloc_sentinel ils (EXPR_LOCATION (TREE_TYPE (mem_inits)));
+
       perform_member_init (TREE_PURPOSE (mem_inits),
 			   TREE_VALUE (mem_inits));
       mem_inits = TREE_CHAIN (mem_inits);