From: Jason Merrill <jason@redhat.com>
Date: Fri, 9 May 2025 22:08:43 +0000 (-0400)
Subject: c++: recursive instantiation diagnostic [PR120204]
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=b5f61a09c1ab3a45398333b50963e533a980b62d;p=thirdparty%2Fgcc.git

c++: recursive instantiation diagnostic [PR120204]

Here tsubst_baselink was returning error_mark_node silently despite
tf_error; we need to actually give an error.

	PR c++/120204

gcc/cp/ChangeLog:

	* pt.cc (tsubst_baselink): Always error if lookup fails.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/constexpr-recursion3.C: New test.
---

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 09f74a2814b..0d64a1cfb12 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -17477,10 +17477,18 @@ tsubst_baselink (tree baselink, tree object_type,
 
       if (!baselink)
 	{
-	  if ((complain & tf_error)
-	      && constructor_name_p (name, qualifying_scope))
-	    error ("cannot call constructor %<%T::%D%> directly",
-		   qualifying_scope, name);
+	  if (complain & tf_error)
+	    {
+	      if (constructor_name_p (name, qualifying_scope))
+		error ("cannot call constructor %<%T::%D%> directly",
+		       qualifying_scope, name);
+	      else
+		/* Lookup succeeded at parse time, but failed during
+		   instantiation; must be because we're trying to refer to it
+		   while forming its declaration (c++/120204).  */
+		error ("declaration of %<%T::%D%> depends on itself",
+		       qualifying_scope, name);
+	    }
 	  return error_mark_node;
 	}
 
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-recursion3.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-recursion3.C
new file mode 100644
index 00000000000..cadbdf08c97
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-recursion3.C
@@ -0,0 +1,15 @@
+// PR c++/120204
+// { dg-do compile { target c++14 } }
+
+template<class T, int t>
+struct array{};
+
+template <typename... TArgs> struct ILEArglist {
+  using Sizes = array<int, sizeof...(TArgs)>;
+  static constexpr int size() {	// { dg-bogus "not usable" }
+    Sizes &offsets_c = offsets;	// { dg-error "depends on itself" }
+    return 0;
+  }
+  array<char, size()> offsets(); // { dg-error "constant expression" }
+};
+auto arglist = ILEArglist<>();