[lldb] Make CompilerDecl::GetName (always) return template args (#116068)

I ran into this while look at a different bug (patch coming soon). This
function has only two callers. The first is SBTypeStaticField::GetName
(which doesn't care about templates), and the other is
CompilerDecl::GetCompilerContext (in the TypeQuery constructor), which
does want template arguments.

This function was (normally) returning the name without template args.
Since this code is only used when looking up a type in another shared
library, the odds of running into this bug are relatively low, but I add
a test to demonstrate the scenario and the fix for it nonetheless.

Amazingly (and scarily), this test actually passes without this change
in the default configuration -- and only fails with
-gsimple-template-names. The reason for that is that in the
non-simplified case we create a regular CXXRecordDecl whose name is
"bar<int>" (instead of a template record "foo" with an argument of
"int"). When evaluating the expression, we are somehow able to replace
this with a proper template specialization decl.

Author: labath

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

@@ -9116,7 +9116,7 @@ ConstString TypeSystemClang::DeclGetName(void *opaque_decl) {
     clang::NamedDecl *nd =
         llvm::dyn_cast<NamedDecl>((clang::Decl *)opaque_decl);
     if (nd != nullptr)
-      return ConstString(nd->getDeclName().getAsString());
+      return ConstString(GetTypeNameForDecl(nd, /*qualified=*/false));
   }
   return ConstString();
 }

lldb/test/API/lang/cpp/forward/Makefile

@@ -0,0 +1,5 @@
+CXX_SOURCES := main.cpp
+DYLIB_CXX_SOURCES := foo.cpp
+DYLIB_NAME := foo
+
+include Makefile.rules

lldb/test/API/lang/cpp/forward/TestCPPForwardDeclaration.py

@@ -0,0 +1,61 @@
+"""Test that forward declaration of a c++ template gets resolved correctly."""
+
+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test.decorators import *
+import lldbsuite.test.lldbutil as lldbutil
+
+
+class ForwardDeclarationTestCase(TestBase):
+    def do_test(self, dictionary=None):
+        """Display *bar_ptr when stopped on a function with forward declaration of struct bar."""
+        self.build(dictionary=dictionary)
+        exe = self.getBuildArtifact("a.out")
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+
+        environment = self.registerSharedLibrariesWithTarget(target, ["foo"])
+
+        # Break inside the foo function which takes a bar_ptr argument.
+        lldbutil.run_break_set_by_symbol(self, "foo", num_expected_locations=1)
+
+        process = target.LaunchSimple(
+            None, environment, self.get_process_working_directory()
+        )
+        self.assertTrue(process, PROCESS_IS_VALID)
+
+        # The stop reason of the thread should be breakpoint.
+        self.expect(
+            "thread list",
+            STOPPED_DUE_TO_BREAKPOINT,
+            substrs=["stopped", "stop reason = breakpoint"],
+        )
+
+        # The breakpoint should have a hit count of 1.
+        lldbutil.check_breakpoint(self, bpno=1, expected_hit_count=1)
+
+        self.expect_expr(
+            "*bar_ptr",
+            result_type="bar<int>",
+            result_children=[ValueCheck(value="47", name="a", type="int")],
+        )
+
+    def test(self):
+        self.do_test()
+
+    @no_debug_info_test
+    @skipIfDarwin
+    @skipIf(compiler=no_match("clang"))
+    @skipIf(compiler_version=["<", "8.0"])
+    @expectedFailureAll(oslist=["windows"])
+    def test_debug_names(self):
+        """Test that we are able to find complete types when using DWARF v5
+        accelerator tables"""
+        self.do_test(dict(CFLAGS_EXTRAS="-gdwarf-5 -gpubnames"))
+
+    @no_debug_info_test
+    @skipIf(compiler=no_match("clang"))
+    def test_simple_template_names(self):
+        """Test that we are able to find complete types when using DWARF v5
+        accelerator tables"""
+        self.do_test(dict(CFLAGS_EXTRAS="-gsimple-template-names"))

lldb/test/API/lang/cpp/forward/foo.cpp

@@ -0,0 +1,3 @@
+#include "foo.h"
+
+int foo(bar<int> *bar_ptr) { return 1; }

lldb/test/API/lang/cpp/forward/foo.h

@@ -0,0 +1,3 @@
+template <typename T> struct bar;
+
+LLDB_TEST_API int foo(bar<int> *bar_ptr);

lldb/test/API/lang/cpp/forward/main.cpp

@@ -0,0 +1,13 @@
+#include "foo.h"
+
+template <typename T> struct bar {
+  T a;
+};
+
+int main() {
+  bar<int> b{47};
+
+  foo(&b);
+
+  return 0;
+}