c++: ICE with nested default targ lambdas [PR119574]

In GCC 14 we fixed PR116567 in a more conservative way that doesn't
distinguish between the two kinds of deferred substitutions, and so
for PR119574 we instead ICE from get_innermost_template_args due to
TMPL_PARMS_DEPTH of the lambda, 2, being greater than the depth of the
augmented args, 1.

This patch works around the ICE in a best effort kind of way by guarding
the get_innermost_template_args call appropriately; I don't think it's
possible to get this completely right in GCC 14 without backporting the
proper fix for PR116567.

Note that lambda-targ13b.C present in the GCC 15 version of this patch[1]
never worked in GCC 14, and still doesn't work, which is why it's not
present in this patch.

[1]: r15-9350-gf3862ab07943d1

	PR c++/119574

gcc/cp/ChangeLog:

	* pt.cc (tsubst_lambda_expr): Don't call
	get_innermost_template_args if we're requesting too many
	levels.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/lambda-targ13.C: New test.
	* g++.dg/cpp2a/lambda-targ13a.C: New test.

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 2efc7eb19e87a855d47ae0d0a93d289fea11d6e1..5b9a9c611f244ae191bb0d218028201fdd25fb2e 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -19708,7 +19708,8 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
       tree ctx_parms = DECL_TEMPLATE_PARMS (DECL_TI_TEMPLATE (oldfn));
       if (generic_lambda_fn_p (oldfn))
        ctx_parms = TREE_CHAIN (ctx_parms);
-      args = get_innermost_template_args (args, TMPL_PARMS_DEPTH (ctx_parms));
+      if (TMPL_ARGS_DEPTH (args) > TMPL_PARMS_DEPTH (ctx_parms))
+       args = get_innermost_template_args (args, TMPL_PARMS_DEPTH (ctx_parms));
     }
 
   tree r = build_lambda_expr ();

diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-targ13.C b/gcc/testsuite/g++.dg/cpp2a/lambda-targ13.C
new file mode 100644 (file)
index 0000000..8fd0a31
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-targ13.C
@@ -0,0 +1,7 @@
+// PR c++/119574
+// { dg-do compile { target c++20 } }
+
+template <class F = decltype([] <auto G = [] {}> () {})>
+void f(F op = {}) { op(); }
+
+int main() { f(); }

diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-targ13a.C b/gcc/testsuite/g++.dg/cpp2a/lambda-targ13a.C
new file mode 100644 (file)
index 0000000..8aaefd9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-targ13a.C
@@ -0,0 +1,8 @@
+// PR c++/119574
+// A version of lambda-targ13.C with extra template parameters.
+// { dg-do compile { target c++20 } }
+
+template <int = 0, class F = decltype([] <int = 1, auto G = [] {}> () {})>
+void f(F op = {}) { op(); }
+
+int main() { f(); }