Fix scope-based lookup when more than one function is found.

When multiple functions are found by name, lldb removes duplicate entries of
functions with the same type, so the first function in the symbol context list
is chosen, even if it isn't in scope. This patch uses the declaration context
of the execution context to select the function which is in scope.

This fixes cases like the following:

    int func();
    namespace ns {
	int func();
	void here() {
	    // Run to BP here and eval 'p func()';
	    // lldb used to find ::func(), now finds ns::func().
	}
    }

Reviewed by: clayborg
Subscribers: lldb-commits
Differential Revision: http://reviews.llvm.org/D15312

llvm-svn: 255439

1 files changed, 122 insertions, 0 deletions

diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp
index a367b4414b4..c9bc4b6487c 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp
@@ -1424,6 +1424,128 @@ ClangExpressionDeclMap::FindExternalVisibleDecls (NameSearchContext &context,
                                                   sc_list);
             }
 
+            // If we found more than one function, see if we can use the
+            // frame's decl context to remove functions that are shadowed
+            // by other functions which match in type but are nearer in scope.
+            //
+            // AddOneFunction will not add a function whose type has already been
+            // added, so if there's another function in the list with a matching
+            // type, check to see if their decl context is a parent of the current
+            // frame's or was imported via a and using statement, and pick the
+            // best match according to lookup rules.
+            if (sc_list.GetSize() > 1)
+            {
+                // Collect some info about our frame's context.
+                StackFrame *frame = m_parser_vars->m_exe_ctx.GetFramePtr();
+                SymbolContext frame_sym_ctx;
+                if (frame != nullptr)
+                    frame_sym_ctx = frame->GetSymbolContext(lldb::eSymbolContextFunction|lldb::eSymbolContextBlock);
+                CompilerDeclContext frame_decl_context = frame_sym_ctx.block != nullptr ? frame_sym_ctx.block->GetDeclContext() : CompilerDeclContext();
+
+                // We can't do this without a compiler decl context for our frame.
+                if (frame_decl_context)
+                {
+                    clang::DeclContext *frame_decl_ctx = (clang::DeclContext *)frame_decl_context.GetOpaqueDeclContext();
+                    ClangASTContext *ast = llvm::dyn_cast_or_null<ClangASTContext>(frame_decl_context.GetTypeSystem());
+
+                    // Structure to hold the info needed when comparing function
+                    // declarations.
+                    struct FuncDeclInfo
+                    {
+                        ConstString m_name;
+                        CompilerType m_copied_type;
+                        uint32_t m_decl_lvl;
+                        SymbolContext m_sym_ctx;
+                    };
+
+                    // First, symplify things by looping through the symbol contexts
+                    // to remove unwanted functions and separate out the functions we
+                    // want to compare and prune into a separate list.
+                    // Cache the info needed about the function declarations in a
+                    // vector for efficiency.
+                    SymbolContextList sc_sym_list;
+                    uint32_t num_indices = sc_list.GetSize();
+                    std::vector<FuncDeclInfo> fdi_cache;
+                    fdi_cache.reserve(num_indices);
+                    for (uint32_t index = 0; index < num_indices; ++index)
+                    {
+                        FuncDeclInfo fdi;
+                        SymbolContext sym_ctx;
+                        sc_list.GetContextAtIndex(index, sym_ctx);
+
+                        // We don't know enough about symbols to compare them,
+                        // but we should keep them in the list.
+                        Function *function = sym_ctx.function;
+                        if (!function)
+                        {
+                            sc_sym_list.Append(sym_ctx);
+                            continue;
+                        }
+                        // Filter out functions without declaration contexts, as well as
+                        // class/instance methods, since they'll be skipped in the
+                        // code that follows anyway.
+                        CompilerDeclContext func_decl_context = function->GetDeclContext();
+                        if (!func_decl_context || func_decl_context.IsClassMethod(nullptr, nullptr, nullptr))
+                            continue;
+                        // We can only prune functions for which we can copy the type.
+                        CompilerType func_clang_type = function->GetType()->GetFullCompilerType();
+                        CompilerType copied_func_type = GuardedCopyType(func_clang_type);
+                        if (!copied_func_type)
+                        {
+                            sc_sym_list.Append(sym_ctx);
+                            continue;
+                        }
+
+                        fdi.m_sym_ctx = sym_ctx;
+                        fdi.m_name = function->GetName();
+                        fdi.m_copied_type = copied_func_type;
+                        fdi.m_decl_lvl = LLDB_INVALID_DECL_LEVEL;
+                        if (fdi.m_copied_type && func_decl_context)
+                        {
+                            // Call CountDeclLevels to get the number of parent scopes we
+                            // have to look through before we find the function declaration.
+                            // When comparing functions of the same type, the one with a
+                            // lower count will be closer to us in the lookup scope and
+                            // shadows the other.
+                            clang::DeclContext *func_decl_ctx = (clang::DeclContext *)func_decl_context.GetOpaqueDeclContext();
+                            fdi.m_decl_lvl = ast->CountDeclLevels(frame_decl_ctx,
+                                                                  func_decl_ctx,
+                                                                  &fdi.m_name,
+                                                                  &fdi.m_copied_type);
+                        }
+                        fdi_cache.emplace_back(fdi);
+                    }
+
+                    // Loop through the functions in our cache looking for matching types,
+                    // then compare their scope levels to see which is closer.
+                    std::multimap<CompilerType, const FuncDeclInfo*> matches;
+                    for (const FuncDeclInfo &fdi : fdi_cache)
+                    {
+                        const CompilerType t = fdi.m_copied_type;
+                        auto q = matches.find(t);
+                        if (q != matches.end())
+                        {
+                            if (q->second->m_decl_lvl > fdi.m_decl_lvl)
+                                // This function is closer; remove the old set.
+                                matches.erase(t);
+                            else if (q->second->m_decl_lvl < fdi.m_decl_lvl)
+                                // The functions in our set are closer - skip this one.
+                                continue;
+                        }
+                        matches.insert(std::make_pair(t, &fdi));
+                    }
+
+                    // Loop through our matches and add their symbol contexts to our list.
+                    SymbolContextList sc_func_list;
+                    for (const auto &q : matches)
+                        sc_func_list.Append(q.second->m_sym_ctx);
+
+                    // Rejoin the lists with the functions in front.
+                    sc_list = sc_func_list;
+                    sc_list.Append(sc_sym_list);
+                }
+            }
+
             if (sc_list.GetSize())
             {
                 Symbol *extern_symbol = NULL;