Now that with r14-11-g2245459c85a3f4 made us coerce the template
arguments of a bound ttp again after level-lowering, this unfortunately
causes a crash from coerce_template_args_for_ttp in the below testcase.
During the level-lowering substitution T=int into the bound ttp TT<int>
as part of substitution into the lambda signature, current_template_parms
is just U=U rather than the ideal TT=TT, U=U. And because we don't
consistently set DECL_CONTEXT for level-lowered ttps (it's kind of a
chicken of the egg problem in this case), we attempt to use
current_template_parms to obtain the outer arguments during
coerce_template_args_for_ttp. But the depth 1 of c_t_p
current_template_parms is less than the depth 2 of the level-lowered TT,
and we end up segfaulting from there.
So for level-lowered ttps it seems we need to get the outer arguments a
different way -- namely, we can look at the trailing parms of its
DECL_TEMPLATE_PARMS.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/13?
PR c++/109651
gcc/cp/ChangeLog:
* pt.cc (coerce_template_args_for_ttp): For level-lowered
ttps with DECL_CONTEXT not set, obtain the outer template
arguments via its DECL_TEMPLATE_PARMS.
gcc/testsuite/ChangeLog:
* g++.dg/template/ttp37.C: New test.
---
gcc/cp/pt.cc | 5 +++++
gcc/testsuite/g++.dg/template/ttp37.C | 11 +++++++++++
2 files changed, 16 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/template/ttp37.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 678cb7930e3..bbde61061f6 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -7872,6 +7872,11 @@ coerce_template_args_for_ttp (tree templ, tree arglist,
tree outer = DECL_CONTEXT (templ);
if (outer)
outer = generic_targs_for (outer);
+ else if (TEMPLATE_TYPE_LEVEL (TREE_TYPE (templ))
+ != TEMPLATE_TYPE_ORIG_LEVEL (TREE_TYPE (templ)))
+ /* This is a level-lowered template template parameter, for which
+ we don't consistently set DECL_CONTEXT (FIXME). */
+ outer = template_parms_to_args (TREE_CHAIN (DECL_TEMPLATE_PARMS (templ)));
else if (current_template_parms)
{
/* This is an argument of the current template, so we haven't set
diff --git a/gcc/testsuite/g++.dg/template/ttp37.C
b/gcc/testsuite/g++.dg/template/ttp37.C
new file mode 100644
index 00000000000..876e5b6232a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp37.C
@@ -0,0 +1,11 @@
+// PR c++/109651
+// { dg-do compile { target c++20 } }
+
+template<class T>
+void f() {
+ []<class U>() {
+ []<template<class> class TT>(TT<int>) { };
+ };
+}
+
+template void f<int>();
--
2.40.1.423.g2807bd2c10
