From 77772f8a3da8ea30066d2201f8148714a8e89da5 Mon Sep 17 00:00:00 2001
From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Tue, 5 Mar 2024 15:17:09 +1100
Subject: [PATCH] c++: Stream DECL_CONTEXT for template template parms
 [PR98881]

When streaming in a nested template-template parameter as in the
attached testcase, we end up reaching the containing template-template
parameter in 'tpl_parms_fini'. We should not set the DECL_CONTEXT to
this (nested) template-template parameter, as it should already be the
struct that the outer template-template parameter is declared on.

The precise logic for what DECL_CONTEXT should be for a template
template parameter in various situations seems rather obscure. Rather
than trying to determine the assumptions that need to hold, it seems
simpler to just always re-stream the DECL_CONTEXT as needed for now.

	PR c++/98881

gcc/cp/ChangeLog:

	* module.cc (trees_out::tpl_parms_fini): Stream out DECL_CONTEXT
	for template template parameters.
	(trees_in::tpl_parms_fini): Read it.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/tpl-tpl-parm-3.h: New test.
	* g++.dg/modules/tpl-tpl-parm-3_a.H: New test.
	* g++.dg/modules/tpl-tpl-parm-3_b.C: New test.
	* g++.dg/modules/tpl-tpl-parm-3_c.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Reviewed-by: Jason Merrill <jason@redhat.com>
---
 gcc/cp/module.cc                              | 41 +++++--------------
 gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3.h | 12 ++++++
 .../g++.dg/modules/tpl-tpl-parm-3_a.H         |  5 +++
 .../g++.dg/modules/tpl-tpl-parm-3_b.C         |  5 +++
 .../g++.dg/modules/tpl-tpl-parm-3_c.C         | 15 +++++++
 5 files changed, 47 insertions(+), 31 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3.h
 create mode 100644 gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_a.H
 create mode 100644 gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_b.C
 create mode 100644 gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_c.C

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 80b63a70a62c..f7e8b357fc2d 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -10126,23 +10126,12 @@ trees_out::tpl_parms_fini (tree tmpl, unsigned tpl_levels)
 	  tree dflt = TREE_PURPOSE (parm);
 	  tree_node (dflt);
 
-	  if (streaming_p ())
-	    {
-	      tree decl = TREE_VALUE (parm);
-	      if (TREE_CODE (decl) == TEMPLATE_DECL)
-		{
-		  tree ctx = DECL_CONTEXT (decl);
-		  tree inner = DECL_TEMPLATE_RESULT (decl);
-		  tree tpi = (TREE_CODE (inner) == TYPE_DECL
-			      ? TEMPLATE_TYPE_PARM_INDEX (TREE_TYPE (decl))
-			      : DECL_INITIAL (inner));
-		  bool original = (TEMPLATE_PARM_LEVEL (tpi)
-				   == TEMPLATE_PARM_ORIG_LEVEL (tpi));
-		  /* Original template template parms have a context
-		     of their owning template.  Reduced ones do not.  */
-		  gcc_checking_assert (original ? ctx == tmpl : !ctx);
-		}
-	    }
+	  /* Template template parameters need a context of their owning
+	     template. This is quite tricky to infer correctly on stream-in
+	     (see PR c++/98881) so we'll just provide it directly.  */
+	  tree decl = TREE_VALUE (parm);
+	  if (TREE_CODE (decl) == TEMPLATE_DECL)
+	    tree_node (DECL_CONTEXT (decl));
 	}
     }
 }
@@ -10160,24 +10149,14 @@ trees_in::tpl_parms_fini (tree tmpl, unsigned tpl_levels)
 	{
 	  tree parm = TREE_VEC_ELT (vec, ix);
 	  tree dflt = tree_node ();
-	  if (get_overrun ())
-	    return false;
 	  TREE_PURPOSE (parm) = dflt;
 
 	  tree decl = TREE_VALUE (parm);
 	  if (TREE_CODE (decl) == TEMPLATE_DECL)
-	    {
-	      tree inner = DECL_TEMPLATE_RESULT (decl);
-	      tree tpi = (TREE_CODE (inner) == TYPE_DECL
-			  ? TEMPLATE_TYPE_PARM_INDEX (TREE_TYPE (decl))
-			  : DECL_INITIAL (inner));
-	      bool original = (TEMPLATE_PARM_LEVEL (tpi)
-			       == TEMPLATE_PARM_ORIG_LEVEL (tpi));
-	      /* Original template template parms have a context
-		 of their owning template.  Reduced ones do not.  */
-	      if (original)
-		DECL_CONTEXT (decl) = tmpl;
-	    }
+	    DECL_CONTEXT (decl) = tree_node ();
+
+	  if (get_overrun ())
+	    return false;
 	}
     }
   return true;
diff --git a/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3.h b/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3.h
new file mode 100644
index 000000000000..b0dcf353c239
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3.h
@@ -0,0 +1,12 @@
+// PR c++/98881
+
+template <typename P> struct X {};
+
+template<template <typename> typename TT>
+struct X<TT<int>> {
+  template<template <typename> typename UU>
+  void f (X<UU<int>>&);
+};
+
+template<template<class> class TT> struct Y;
+template<template<class> class UU> struct Y { };
diff --git a/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_a.H b/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_a.H
new file mode 100644
index 000000000000..47464081f250
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_a.H
@@ -0,0 +1,5 @@
+// PR c++/98881
+// { dg-additional-options "-fmodule-header" }
+// { dg-module-cmi {} }
+
+#include "tpl-tpl-parm-3.h"
diff --git a/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_b.C b/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_b.C
new file mode 100644
index 000000000000..1e3cc6c444f2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_b.C
@@ -0,0 +1,5 @@
+// PR c++/98881
+// { dg-additional-options "-fmodules-ts -fno-module-lazy" }
+
+#include "tpl-tpl-parm-3.h"
+import "tpl-tpl-parm-3_a.H";
diff --git a/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_c.C b/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_c.C
new file mode 100644
index 000000000000..5edba6cc64f1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/tpl-tpl-parm-3_c.C
@@ -0,0 +1,15 @@
+// PR c++/98881
+// { dg-additional-options "-fmodules-ts" }
+
+import "tpl-tpl-parm-3_a.H";
+
+template <typename T> struct A {};
+template <typename T> struct B {};
+
+void foo() {
+  X<A<int>> a;
+  X<B<int>> b;
+  a.f(b);
+
+  Y<A> y;
+}
-- 
2.47.2