[lldb][SymbolFileDWARF] Fall back to using parent DW_AT_LLVM_include_path for submodules (llvm#142044)

Inferred submodule declarations are emitted in DWARF as `DW_TAG_module`s
without `DW_AT_LLVM_include_path`s. Instead the parent DIE will have the
include path. This patch adds support for such setups. Without this, the
`ClangModulesDeclVendor` would fail to `AddModule` the submodules (i.e.,
compile and load the submodules). This would cause errors such as:
```
note: error: Header search couldn't locate module 'TopLevel'
```

The test added here also tests
llvm#141220. Without that patch
we'd fail with:
```
note: error: No module map file in /Users/jonas/Git/llvm-worktrees/llvm-project/lldb/test/API/lang/cpp/decl-from-submodule
```

Unfortunately the embedded clang instance doesn't allow us to use the
decls we find in the modules. But we'll try to fix that in a separate
patch.

rdar://151022173

Author: Michael137

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

@@ -1188,17 +1188,25 @@ bool SymbolFileDWARF::ParseImportedModules(
       SourceModule module;
       module.path.push_back(ConstString(name));
 
+      const char *include_path = module_die.GetAttributeValueAsString(
+          DW_AT_LLVM_include_path, nullptr);
       DWARFDIE parent_die = module_die;
       while ((parent_die = parent_die.GetParent())) {
         if (parent_die.Tag() != DW_TAG_module)
           break;
         if (const char *name =
                 parent_die.GetAttributeValueAsString(DW_AT_name, nullptr))
           module.path.push_back(ConstString(name));
+
+        // Inferred submodule declarations may not have a
+        // DW_AT_LLVM_include_path. Pick the parent (aka umbrella) module's
+        // include path instead.
+        if (!include_path)
+          include_path = parent_die.GetAttributeValueAsString(
+              DW_AT_LLVM_include_path, nullptr);
       }
       std::reverse(module.path.begin(), module.path.end());
-      if (const char *include_path = module_die.GetAttributeValueAsString(
-              DW_AT_LLVM_include_path, nullptr)) {
+      if (include_path) {
         FileSpec include_spec(include_path, dwarf_cu->GetPathStyle());
         MakeAbsoluteAndRemap(include_spec, *dwarf_cu,
                              m_objfile_sp->GetModule());

lldb/test/API/lang/cpp/decl-from-submodule/Makefile

@@ -0,0 +1,4 @@
+CXX_SOURCES := main.cpp
+CXXFLAGS_EXTRAS = $(MANDATORY_MODULE_BUILD_CFLAGS)
+
+include Makefile.rules

lldb/test/API/lang/cpp/decl-from-submodule/TestDeclFromSubmodule.py

@@ -0,0 +1,25 @@
+"""Test that decl lookup into submodules in C++ works as expected."""
+
+import lldb
+import shutil
+
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class DeclFromSubmoduleTestCase(TestBase):
+    def test_expr(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "return 0", lldb.SBFileSpec("main.cpp"))
+
+        # FIXME: LLDB finds the decl for 'func' in the submodules correctly and hands it to Clang
+        # but Sema rejects using the decl during name lookup because it is not marked "Visible".
+        # However, this assertions still ensures that we at least don't fail to compile the
+        # submodule (which would cause other errors to appear before the expression error, hence
+        # we use "startstr").
+        self.expect(
+            "expr func(1, 2)",
+            error=True,
+            startstr="error: <user expression 0>:1:1: 'func' has unknown return type",
+        )

lldb/test/API/lang/cpp/decl-from-submodule/TopLevel/module1.h

@@ -0,0 +1,2 @@
+// nodebug to force LLDB to find the decls in modules
+[[gnu::nodebug]] inline int func(int x) { return x; }

lldb/test/API/lang/cpp/decl-from-submodule/TopLevel/module2.h

@@ -0,0 +1,2 @@
+// nodebug to force LLDB to find the decls in modules
+[[gnu::nodebug]] inline int func(int x, int y) { return x + y; }

lldb/test/API/lang/cpp/decl-from-submodule/main.cpp

@@ -0,0 +1,9 @@
+#include "TopLevel/module1.h"
+#include "TopLevel/module2.h"
+
+int main() {
+  func(1);
+  func(2, 3);
+
+  return 0;
+}

lldb/test/API/lang/cpp/decl-from-submodule/module.modulemap

@@ -0,0 +1,6 @@
+module TopLevel {
+  umbrella "TopLevel"
+  explicit module * {
+    export *
+  }
+}