From 7bfb1550ccea7c426d50244e980f01f30db8ba0c Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Sun, 7 May 2023 11:54:21 -0400
Subject: [PATCH] c++: bound ttp in lambda function type [PR109651]
After r14-11-g2245459c85a3f4 we now coerce the template arguments of a
bound ttp again after level-lowering it. Notably a level-lowered ttp
doesn't have DECL_CONTEXT set, so during this coercion we fall back to
using current_template_parms to obtain the relevant set of in-scope
parameters.
But it turns out current_template_parms isn't properly set when
substituting the function type of a generic lambda, and so if the type
contains bound ttps that need to be lowered we'll crash during their
attempted coercion. Specifically in the first testcase below,
current_template_parms during the lambda type substitution (with T=int)
is "1 U" instead of the expected "2 TT, 1 U", and we crash when level
lowering TT<int>.
Ultimately the problem is that tsubst_lambda_expr does things in the
wrong order: we ought to substitute (and install) the in-scope template
parameters _before_ substituting anything that may use those template
parameters (such as the function type of a generic lambda). This patch
corrects this substitution order.
PR c++/109651
gcc/cp/ChangeLog:
* pt.cc (coerce_template_args_for_ttp): Mention we can hit the
current_template_parms fallback when level-lowering a bound ttp.
(tsubst_template_decl): Add lambda_tparms parameter. Prefer to
use lambda_tparms instead of substituting DECL_TEMPLATE_PARMS.
(tsubst_decl) <case TEMPLATE_DECL>: Pass NULL_TREE as lambda_tparms
to tsubst_template_decl.
(tsubst_lambda_expr): For a generic lambda, substitute
DECL_TEMPLATE_PARMS and set current_template_parms to it
before substituting the function type. Pass the substituted
DECL_TEMPLATE_PARMS as lambda_tparms to tsubst_template_decl.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/lambda-generic-ttp1.C: New test.
* g++.dg/cpp2a/lambda-generic-ttp2.C: New test.
---
gcc/cp/pt.cc | 34 ++++++++++++++-----
.../g++.dg/cpp2a/lambda-generic-ttp1.C | 11 ++++++
.../g++.dg/cpp2a/lambda-generic-ttp2.C | 13 +++++++
3 files changed, 50 insertions(+), 8 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-generic-ttp1.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-generic-ttp2.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 0f4fb258f9eb..ee4a2f313430 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -7880,7 +7880,8 @@ coerce_template_args_for_ttp (tree templ, tree arglist,
else if (current_template_parms)
{
/* This is an argument of the current template, so we haven't set
- DECL_CONTEXT yet. */
+ DECL_CONTEXT yet. We can also get here when level-lowering a
+ bound ttp. */
tree relevant_template_parms;
/* Parameter levels that are greater than the level of the given
@@ -14614,7 +14615,7 @@ tsubst_function_decl (tree t, tree args, tsubst_flags_t complain,
static tree
tsubst_template_decl (tree t, tree args, tsubst_flags_t complain,
- tree lambda_fntype)
+ tree lambda_fntype, tree lambda_tparms)
{
/* We can get here when processing a member function template,
member class template, or template template parameter. */
@@ -14704,8 +14705,10 @@ tsubst_template_decl (tree t, tree args, tsubst_flags_t complain,
auto tparm_guard = make_temp_override (current_template_parms);
DECL_TEMPLATE_PARMS (r)
= current_template_parms
- = tsubst_template_parms (DECL_TEMPLATE_PARMS (t), args,
- complain);
+ = (lambda_tparms
+ ? lambda_tparms
+ : tsubst_template_parms (DECL_TEMPLATE_PARMS (t), args,
+ complain));
bool class_p = false;
tree inner = decl;
@@ -14876,7 +14879,9 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
switch (TREE_CODE (t))
{
case TEMPLATE_DECL:
- r = tsubst_template_decl (t, args, complain, /*lambda*/NULL_TREE);
+ r = tsubst_template_decl (t, args, complain,
+ /*lambda_fntype=*/NULL_TREE,
+ /*lambda_tparms=*/NULL_TREE);
break;
case FUNCTION_DECL:
@@ -20121,12 +20126,24 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
? DECL_TI_TEMPLATE (oldfn)
: NULL_TREE);
+ tree tparms = NULL_TREE;
+ if (oldtmpl)
+ tparms = tsubst_template_parms (DECL_TEMPLATE_PARMS (oldtmpl), args, complain);
+
tree fntype = static_fn_type (oldfn);
+
+ tree saved_ctp = current_template_parms;
if (oldtmpl)
- ++processing_template_decl;
+ {
+ ++processing_template_decl;
+ current_template_parms = tparms;
+ }
fntype = tsubst (fntype, args, complain, in_decl);
if (oldtmpl)
- --processing_template_decl;
+ {
+ current_template_parms = saved_ctp;
+ --processing_template_decl;
+ }
if (fntype == error_mark_node)
r = error_mark_node;
@@ -20142,7 +20159,8 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
type_memfn_quals (fntype),
type_memfn_rqual (fntype));
tree inst = (oldtmpl
- ? tsubst_template_decl (oldtmpl, args, complain, fntype)
+ ? tsubst_template_decl (oldtmpl, args, complain,
+ fntype, tparms)
: tsubst_function_decl (oldfn, args, complain, fntype));
if (inst == error_mark_node)
{
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-generic-ttp1.C b/gcc/testsuite/g++.dg/cpp2a/lambda-generic-ttp1.C
new file mode 100644
index 000000000000..27b56fc199c4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-generic-ttp1.C
@@ -0,0 +1,11 @@
+// PR c++/109651
+// { dg-do compile { target c++20 } }
+
+template<class T>
+void f() {
+ []<class U>(U) {
+ []<template<class> class TT>(TT<int>) { };
+ }(0);
+}
+
+template void f<int>();
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-generic-ttp2.C b/gcc/testsuite/g++.dg/cpp2a/lambda-generic-ttp2.C
new file mode 100644
index 000000000000..dc2029d7227e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-generic-ttp2.C
@@ -0,0 +1,13 @@
+// PR c++/109651
+// { dg-do compile { target c++20 } }
+
+template<class T>
+auto f() {
+ return []<class U, template<class V, U, V> class TT>(U, TT<int, 1, 2>) { };
+}
+
+template<class T, int N, int M> struct A { };
+
+int main() {
+ f<int>()(0, A<int, 1, 2>{});
+}
--
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