[lldb] Fix name lookup in ClangASTContext

[evgeny777]

Summary

The check for already searched namespaces has disappeared from DeclContextFindDeclByName() recently. This breaks variable evaluation in many cases, for example in this one

namespace ns1 {
    int var = 100;
}

namespace ns2 {
    int var = 101;
}

int main(void) {
    {
        using namespace ns1;
        printf("var=%d\n", var); // evaluation fails - multiple candidates
    }

    {
        using namespace ns2;
        printf("var=%d\n", var); // evaluation fails - multiple candidates
    }
}

[tberghammer]

Please create a test case for this scenario so it won't break again

[evgeny777]

Added test case

[tberghammer]

Te test case looks good to me. Thanks for adding it.

For the actual code change I don' know enough about this area to say anything so please wait for a feedback from Greg.

[dawn]

Patch is correct - without it we loop through the same decl context again. I've tested it locally - there are no new regressions.

[dawn]

See inline comment.

source/Symbol/ClangASTContext.cpp

9102

Minor efficiency improvement - change these 3 lines to:

if (!searched.insert(it->second).first)
    continue;

No need for new patch - just change in final commit.

source/Symbol/ClangASTContext.cpp

if (opaque_decl_ctx)
         SymbolFile *symbol_file = GetSymbolFile();
 
         for (clang::DeclContext *decl_context = root_decl_ctx; decl_context != nullptr && found_decls.empty(); decl_context = decl_context->getParent())
         {
             search_queue.insert(std::make_pair(decl_context, decl_context));
 
             for (auto it = search_queue.find(decl_context); it != search_queue.end(); it++)
             {
+                if (searched.find(it->second) != searched.end())
+                    continue;
                 searched.insert(it->second);
                 symbol_file->ParseDeclsForContext(CompilerDeclContext(this, it->second));
 
                 for (clang::Decl *child : it->second->decls())
                 {
                     if (clang::UsingDirectiveDecl *ud = llvm::dyn_cast<clang::UsingDirectiveDecl>(child))
                     {
                         clang::DeclContext *from = ud->getCommonAncestor();
                         if (searched.find(ud->getNominatedNamespace()) == searched.end())