[sync] Take the three final fork commits ahead of archival

src/CPyCppyy/src/CPyCppyyModule.cxx

@@ -385,7 +385,7 @@ static PyObject* MakeCppTemplateClass(PyObject* /* self */, PyObject* args)
     if (!scope) {
       PyErr_Format(PyExc_TypeError,
                    "Template instantiation failed: '%s' with args: '%s\n'",
-                   Cppyy::GetScopedFinalName(cppscope).c_str(),
+                   Cppyy::GetScopedFinalName(tmpl).c_str(),
                    CPyCppyy_PyText_AsString(PyObject_Repr(args)));
       return nullptr;
     }

src/backend/clingwrapper.cxx

@@ -541,7 +541,10 @@ bool Cppyy::AppendTypesSlow(const std::string& name,
 
   for (const std::string& candidate : candidates) {
     std::string var = "__Cppyy_s" + std::to_string(struct_count++);
-    if (!Cpp::Declare(("__Cppyy_AppendTypesSlow<" + candidate + "> " + var + ";\n").c_str(), /*silent=*/true)) {
+    // nodebug: with -g the variable's debug info would carry the full DIE
+    // tree of every template argument (all member declarations included) --
+    // a large, uncacheable per-lookup cost on heavyweight types.
+    if (!Cpp::Declare(("__Cppyy_AppendTypesSlow<" + candidate + "> __attribute__((nodebug)) " + var + ";\n").c_str(), /*silent=*/true)) {
       TCppType_t varN =
           Cpp::GetVariableType(Cpp::GetNamed(var.c_str(), /*parent=*/nullptr));
       TCppScope_t instance_class = Cpp::GetScopeFromType(varN);

test/test_templates.py

@@ -1334,6 +1334,21 @@ def test39_monkey_patching_template_proxy(self):
         assert a.m([1, 2, 3])
         assert not a.m(42)
 
+    def test40_instantiation_failure_error_message(self):
+        """Rejected instantiation names the template, not garbage"""
+
+        import cppyy
+
+        cppyy.cppdef("namespace errpath { template <unsigned N> struct Buf { int tag; }; }")
+
+        # Check that the failed instantiation error message contains the
+        # correct template name.
+        with raises(TypeError) as exc:
+            cppyy.gbl.errpath.Buf["int"]
+        msg = str(exc.value)
+        assert "errpath::Buf" in msg
+        assert "<unnamed>" not in msg
+
 
 @mark.skipif((IS_MAC and IS_CLING), reason="setup class fails with OS X cling")
 class TestTEMPLATED_TYPEDEFS: