Narrow the CompletionRequest API to being append-only.

Summary:
We currently allow any completion handler to read and manipulate the list of matches we
calculated so far. This leads to a few problems:

Firstly, a completion handler's logic can now depend on previously calculated results
by another handlers. No completion handler should have such an implicit dependency,
but the current API makes it likely that this could happen (or already happens). Especially
the fact that some completion handler deleted all previously calculated results can mess
things up right now.

Secondly, all completion handlers have knowledge about our internal data structures with
this API. This makes refactoring this internal data structure much harder than it should be.
Especially planned changes like the support of descriptions for completions are currently
giant patches because we have to refactor every single completion handler.

This patch narrows the contract the CompletionRequest has with the different handlers to:

1. A handler can suggest a completion.
2. A handler can ask how many suggestions we already have.

Point 2 obviously means we still have a  dependency left between the different handlers, but
getting rid of this is too large to just append it to this patch.

Otherwise this patch just completely hides the internal StringList to the different handlers.

The CompletionRequest API now also ensures that the list of completions is unique and we
don't suggest the same value multiple times to the user. This property has been so far only
been ensured by the `Option` handler, but is now applied globally. This is part of this patch
as the OptionHandler is no longer able to implement this functionality itself.

Reviewers: jingham, davide, labath

Reviewed By: davide

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D49322

llvm-svn: 338151

26 files changed, 225 insertions, 130 deletions

diff --git a/lldb/include/lldb/Utility/CompletionRequest.h b/lldb/include/lldb/Utility/CompletionRequest.h
index cfae16f..ef75474 100644
--- a/lldb/include/lldb/Utility/CompletionRequest.h
+++ b/lldb/include/lldb/Utility/CompletionRequest.h
@@ -13,6 +13,7 @@
 #include "lldb/Utility/Args.h"
 #include "lldb/Utility/StringList.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
 
 namespace lldb_private {
 
@@ -77,8 +78,29 @@ public:
 
   void SetWordComplete(bool v) { m_word_complete = v; }
 
-  /// The array of matches returned.
-  StringList &GetMatches() { return *m_matches; }
+  /// Adds a possible completion string. If the completion was already
+  /// suggested before, it will not be added to the list of results. A copy of
+  /// the suggested completion is stored, so the given string can be free'd
+  /// afterwards.
+  ///
+  /// @param match The suggested completion.
+  void AddCompletion(llvm::StringRef completion) {
+    // Add the completion if we haven't seen the same value before.
+    if (m_match_set.insert(completion).second)
+      m_matches->AppendString(completion);
+  }
+
+  /// Adds multiple possible completion strings.
+  ///
+  /// \param completions The list of completions.
+  ///
+  /// @see AddCompletion
+  void AddCompletions(const StringList &completions) {
+    for (std::size_t i = 0; i < completions.GetSize(); ++i)
+      AddCompletion(completions.GetStringAtIndex(i));
+  }
+
+  std::size_t GetNumberOfMatches() const { return m_matches->GetSize(); }
 
   llvm::StringRef GetCursorArgument() const {
     return GetParsedLine().GetArgumentAtIndex(GetCursorIndex());
@@ -111,8 +133,15 @@ private:
   /// \btrue if this is a complete option value (a space will be inserted
   /// after the completion.)  \bfalse otherwise.
   bool m_word_complete = false;
-  // We don't own the list.
+
+  // Note: This list is kept private. This is by design to prevent that any
+  // completion depends on any already computed completion from another backend.
+  // Note: We don't own the list. It's owned by the creator of the
+  // CompletionRequest object.
   StringList *m_matches;
+
+  /// List of added completions so far. Used to filter out duplicates.
+  llvm::StringSet<> m_match_set;
 };
 
 } // namespace lldb_private
diff --git a/lldb/source/Commands/CommandCompletions.cpp b/lldb/source/Commands/CommandCompletions.cpp
index bdfdbb8..7b351c5 100644
--- a/lldb/source/Commands/CommandCompletions.cpp
+++ b/lldb/source/Commands/CommandCompletions.cpp
@@ -90,7 +90,7 @@ int CommandCompletions::SourceFiles(CommandInterpreter &interpreter,
   } else {
     completer.DoCompletion(searcher);
   }
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
 
 static int DiskFilesOrDirectories(const llvm::Twine &partial_name,
@@ -103,7 +103,7 @@ static int DiskFilesOrDirectories(const llvm::Twine &partial_name,
   partial_name.toVector(CompletionBuffer);
 
   if (CompletionBuffer.size() >= PATH_MAX)
-    return 0;
+    return matches.GetSize();
 
   namespace fs = llvm::sys::fs;
   namespace path = llvm::sys::path;
@@ -145,7 +145,7 @@ static int DiskFilesOrDirectories(const llvm::Twine &partial_name,
       // Make sure it ends with a separator.
       path::append(CompletionBuffer, path::get_separator());
       matches.AppendString(CompletionBuffer);
-      return 1;
+      return matches.GetSize();
     }
 
     // We want to keep the form the user typed, so we special case this to
@@ -224,13 +224,21 @@ static int DiskFilesOrDirectories(const llvm::Twine &partial_name,
   return matches.GetSize();
 }
 
+static int DiskFilesOrDirectories(CompletionRequest &request,
+                                  bool only_directories) {
+  request.SetWordComplete(false);
+  StandardTildeExpressionResolver resolver;
+  StringList matches;
+  DiskFilesOrDirectories(request.GetCursorArgumentPrefix(), only_directories,
+                         matches, resolver);
+  request.AddCompletions(matches);
+  return request.GetNumberOfMatches();
+}
+
 int CommandCompletions::DiskFiles(CommandInterpreter &interpreter,
                                   CompletionRequest &request,
                                   SearchFilter *searcher) {
-  request.SetWordComplete(false);
-  StandardTildeExpressionResolver Resolver;
-  return DiskFiles(request.GetCursorArgumentPrefix(), request.GetMatches(),
-                   Resolver);
+  return DiskFilesOrDirectories(request, /*only_dirs*/ false);
 }
 
 int CommandCompletions::DiskFiles(const llvm::Twine &partial_file_name,
@@ -242,10 +250,7 @@ int CommandCompletions::DiskFiles(const llvm::Twine &partial_file_name,
 int CommandCompletions::DiskDirectories(CommandInterpreter &interpreter,
                                         CompletionRequest &request,
                                         SearchFilter *searcher) {
-  request.SetWordComplete(false);
-  StandardTildeExpressionResolver Resolver;
-  return DiskDirectories(request.GetCursorArgumentPrefix(),
-                         request.GetMatches(), Resolver);
+  return DiskFilesOrDirectories(request, /*only_dirs*/ true);
 }
 
 int CommandCompletions::DiskDirectories(const llvm::Twine &partial_file_name,
@@ -267,7 +272,7 @@ int CommandCompletions::Modules(CommandInterpreter &interpreter,
   } else {
     completer.DoCompletion(searcher);
   }
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
 
 int CommandCompletions::Symbols(CommandInterpreter &interpreter,
@@ -283,7 +288,7 @@ int CommandCompletions::Symbols(CommandInterpreter &interpreter,
   } else {
     completer.DoCompletion(searcher);
   }
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
 
 int CommandCompletions::SettingsNames(CommandInterpreter &interpreter,
@@ -304,20 +309,23 @@ int CommandCompletions::SettingsNames(CommandInterpreter &interpreter,
   }
 
   size_t exact_matches_idx = SIZE_MAX;
-  const size_t num_matches =
-      g_property_names.AutoComplete(request.GetCursorArgumentPrefix(),
-                                    request.GetMatches(), exact_matches_idx);
+  StringList matches;
+  g_property_names.AutoComplete(request.GetCursorArgumentPrefix(), matches,
+                                exact_matches_idx);
   request.SetWordComplete(exact_matches_idx != SIZE_MAX);
-  return num_matches;
+  request.AddCompletions(matches);
+  return request.GetNumberOfMatches();
 }
 
 int CommandCompletions::PlatformPluginNames(CommandInterpreter &interpreter,
                                             CompletionRequest &request,
                                             SearchFilter *searcher) {
-  const uint32_t num_matches = PluginManager::AutoCompletePlatformName(
-      request.GetCursorArgumentPrefix(), request.GetMatches());
+  StringList new_matches;
+  std::size_t num_matches = PluginManager::AutoCompletePlatformName(
+      request.GetCursorArgumentPrefix(), new_matches);
   request.SetWordComplete(num_matches == 1);
-  return num_matches;
+  request.AddCompletions(new_matches);
+  return request.GetNumberOfMatches();
 }
 
 int CommandCompletions::ArchitectureNames(CommandInterpreter &interpreter,
@@ -409,10 +417,10 @@ CommandCompletions::SourceFileCompleter::DoCompletion(SearchFilter *filter) {
   filter->Search(*this);
   // Now convert the filelist to completions:
   for (size_t i = 0; i < m_matching_files.GetSize(); i++) {
-    m_request.GetMatches().AppendString(
+    m_request.AddCompletion(
         m_matching_files.GetFileSpecAtIndex(i).GetFilename().GetCString());
   }
-  return m_request.GetMatches().GetSize();
+  return m_request.GetNumberOfMatches();
 }
 
 //----------------------------------------------------------------------
@@ -478,9 +486,9 @@ size_t CommandCompletions::SymbolCompleter::DoCompletion(SearchFilter *filter) {
   filter->Search(*this);
   collection::iterator pos = m_match_set.begin(), end = m_match_set.end();
   for (pos = m_match_set.begin(); pos != end; pos++)
-    m_request.GetMatches().AppendString((*pos).GetCString());
+    m_request.AddCompletion((*pos).GetCString());
 
-  return m_request.GetMatches().GetSize();
+  return m_request.GetNumberOfMatches();
 }
 
 //----------------------------------------------------------------------
@@ -517,7 +525,7 @@ Searcher::CallbackReturn CommandCompletions::ModuleCompleter::SearchCallback(
       match = false;
 
     if (match) {
-      m_request.GetMatches().AppendString(cur_file_name);
+      m_request.AddCompletion(cur_file_name);
     }
   }
   return Searcher::eCallbackReturnContinue;
@@ -525,5 +533,5 @@ Searcher::CallbackReturn CommandCompletions::ModuleCompleter::SearchCallback(
 
 size_t CommandCompletions::ModuleCompleter::DoCompletion(SearchFilter *filter) {
   filter->Search(*this);
-  return m_request.GetMatches().GetSize();
+  return m_request.GetNumberOfMatches();
 }
diff --git a/lldb/source/Commands/CommandObjectCommands.cpp b/lldb/source/Commands/CommandObjectCommands.cpp
index 3012ee4..333f720 100644
--- a/lldb/source/Commands/CommandObjectCommands.cpp
+++ b/lldb/source/Commands/CommandObjectCommands.cpp
@@ -241,7 +241,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eDiskFileCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
   Options *GetOptions() override { return &m_options; }
@@ -1429,7 +1429,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eDiskFileCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
   Options *GetOptions() override { return &m_options; }
diff --git a/lldb/source/Commands/CommandObjectFrame.cpp b/lldb/source/Commands/CommandObjectFrame.cpp
index 0183c43..64de14f 100644
--- a/lldb/source/Commands/CommandObjectFrame.cpp
+++ b/lldb/source/Commands/CommandObjectFrame.cpp
@@ -470,7 +470,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eVariablePathCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
diff --git a/lldb/source/Commands/CommandObjectMultiword.cpp b/lldb/source/Commands/CommandObjectMultiword.cpp
index ade1a2d..19fcf60 100644
--- a/lldb/source/Commands/CommandObjectMultiword.cpp
+++ b/lldb/source/Commands/CommandObjectMultiword.cpp
@@ -143,7 +143,7 @@ bool CommandObjectMultiword::Execute(const char *args_string,
 
   if (num_subcmd_matches > 0) {
     error_msg.append(" Possible completions:");
-    for (size_t i = 0; i < num_subcmd_matches; i++) {
+    for (size_t i = 0; i < matches.GetSize(); i++) {
       error_msg.append("\n\t");
       error_msg.append(matches.GetStringAtIndex(i));
     }
@@ -190,21 +190,22 @@ int CommandObjectMultiword::HandleCompletion(CompletionRequest &request) {
   // Any of the command matches will provide a complete word, otherwise the
   // individual completers will override this.
   request.SetWordComplete(true);
-  auto &matches = request.GetMatches();
 
   auto arg0 = request.GetParsedLine()[0].ref;
   if (request.GetCursorIndex() == 0) {
-    AddNamesMatchingPartialString(m_subcommand_dict, arg0, matches);
+    StringList new_matches;
+    AddNamesMatchingPartialString(m_subcommand_dict, arg0, new_matches);
+    request.AddCompletions(new_matches);
 
-    if (matches.GetSize() == 1 && matches.GetStringAtIndex(0) != nullptr &&
-        (arg0 == matches.GetStringAtIndex(0))) {
+    if (new_matches.GetSize() == 1 &&
+        new_matches.GetStringAtIndex(0) != nullptr &&
+        (arg0 == new_matches.GetStringAtIndex(0))) {
       StringList temp_matches;
       CommandObject *cmd_obj = GetSubcommandObject(arg0, &temp_matches);
       if (cmd_obj != nullptr) {
         if (request.GetParsedLine().GetArgumentCount() == 1) {
           request.SetWordComplete(true);
         } else {
-          matches.DeleteStringAtIndex(0);
           request.GetParsedLine().Shift();
           request.SetCursorCharPosition(0);
           request.GetParsedLine().AppendArgument(llvm::StringRef());
@@ -212,14 +213,17 @@ int CommandObjectMultiword::HandleCompletion(CompletionRequest &request) {
         }
       }
     }
-    return matches.GetSize();
+    return new_matches.GetSize();
   } else {
-    CommandObject *sub_command_object = GetSubcommandObject(arg0, &matches);
+    StringList new_matches;
+    CommandObject *sub_command_object = GetSubcommandObject(arg0, &new_matches);
     if (sub_command_object == nullptr) {
-      return matches.GetSize();
+      request.AddCompletions(new_matches);
+      return request.GetNumberOfMatches();
     } else {
       // Remove the one match that we got from calling GetSubcommandObject.
-      matches.DeleteStringAtIndex(0);
+      new_matches.DeleteStringAtIndex(0);
+      request.AddCompletions(new_matches);
       request.GetParsedLine().Shift();
       request.SetCursorIndex(request.GetCursorIndex() - 1);
       return sub_command_object->HandleCompletion(request);
@@ -366,7 +370,6 @@ int CommandObjectProxy::HandleCompletion(CompletionRequest &request) {
   CommandObject *proxy_command = GetProxyCommandObject();
   if (proxy_command)
     return proxy_command->HandleCompletion(request);
-  request.GetMatches().Clear();
   return 0;
 }
 
@@ -375,7 +378,6 @@ int CommandObjectProxy::HandleArgumentCompletion(
   CommandObject *proxy_command = GetProxyCommandObject();
   if (proxy_command)
     return proxy_command->HandleArgumentCompletion(request, opt_element_vector);
-  request.GetMatches().Clear();
   return 0;
 }
 
diff --git a/lldb/source/Commands/CommandObjectPlatform.cpp b/lldb/source/Commands/CommandObjectPlatform.cpp
index f822a8b..22a9a16 100644
--- a/lldb/source/Commands/CommandObjectPlatform.cpp
+++ b/lldb/source/Commands/CommandObjectPlatform.cpp
@@ -181,7 +181,7 @@ public:
   int HandleCompletion(CompletionRequest &request) override {
     CommandCompletions::PlatformPluginNames(GetCommandInterpreter(), request,
                                             nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
   Options *GetOptions() override { return &m_option_group; }
@@ -1583,9 +1583,9 @@ public:
           const uint32_t num_matches = process_infos.GetSize();
           if (num_matches > 0) {
             for (uint32_t i = 0; i < num_matches; ++i) {
-              request.GetMatches().AppendString(
+              request.AddCompletion(llvm::StringRef(
                   process_infos.GetProcessNameAtIndex(i),
-                  process_infos.GetProcessNameLengthAtIndex(i));
+                  process_infos.GetProcessNameLengthAtIndex(i)));
             }
           }
         }
diff --git a/lldb/source/Commands/CommandObjectPlugin.cpp b/lldb/source/Commands/CommandObjectPlugin.cpp
index 1f379a2..13ef6b2 100644
--- a/lldb/source/Commands/CommandObjectPlugin.cpp
+++ b/lldb/source/Commands/CommandObjectPlugin.cpp
@@ -48,7 +48,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eDiskFileCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
diff --git a/lldb/source/Commands/CommandObjectProcess.cpp b/lldb/source/Commands/CommandObjectProcess.cpp
index 3ac2791..eb5a19a 100644
--- a/lldb/source/Commands/CommandObjectProcess.cpp
+++ b/lldb/source/Commands/CommandObjectProcess.cpp
@@ -141,7 +141,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eDiskFileCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
   Options *GetOptions() override { return &m_options; }
@@ -410,9 +410,9 @@ public:
           const size_t num_matches = process_infos.GetSize();
           if (num_matches > 0) {
             for (size_t i = 0; i < num_matches; ++i) {
-              request.GetMatches().AppendString(
+              request.AddCompletion(llvm::StringRef(
                   process_infos.GetProcessNameAtIndex(i),
-                  process_infos.GetProcessNameLengthAtIndex(i));
+                  process_infos.GetProcessNameLengthAtIndex(i)));
             }
           }
         }
diff --git a/lldb/source/Commands/CommandObjectSettings.cpp b/lldb/source/Commands/CommandObjectSettings.cpp
index f259f2f..3db1e35 100644
--- a/lldb/source/Commands/CommandObjectSettings.cpp
+++ b/lldb/source/Commands/CommandObjectSettings.cpp
@@ -172,7 +172,7 @@ insert-before or insert-after.");
         }
       }
     }
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -272,7 +272,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eSettingsNameCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -338,7 +338,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eSettingsNameCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -427,7 +427,7 @@ public:
       CommandCompletions::InvokeCommonCompletionCallbacks(
           GetCommandInterpreter(), CommandCompletions::eSettingsNameCompletion,
           request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -544,7 +544,7 @@ public:
           GetCommandInterpreter(), CommandCompletions::eSettingsNameCompletion,
           request, nullptr);
 
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -644,7 +644,7 @@ public:
           GetCommandInterpreter(), CommandCompletions::eSettingsNameCompletion,
           request, nullptr);
 
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -749,7 +749,7 @@ public:
           GetCommandInterpreter(), CommandCompletions::eSettingsNameCompletion,
           request, nullptr);
 
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -843,7 +843,7 @@ public:
           GetCommandInterpreter(), CommandCompletions::eSettingsNameCompletion,
           request, nullptr);
 
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -924,7 +924,7 @@ public:
           GetCommandInterpreter(), CommandCompletions::eSettingsNameCompletion,
           request, nullptr);
 
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
diff --git a/lldb/source/Commands/CommandObjectTarget.cpp b/lldb/source/Commands/CommandObjectTarget.cpp
index a9062c1..8be43cb 100644
--- a/lldb/source/Commands/CommandObjectTarget.cpp
+++ b/lldb/source/Commands/CommandObjectTarget.cpp
@@ -201,7 +201,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eDiskFileCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -1810,7 +1810,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eModuleCompletion, request,
         nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 };
 
@@ -1851,7 +1851,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eSourceFileCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 };
 
@@ -2393,7 +2393,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eDiskFileCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
 protected:
@@ -3987,7 +3987,7 @@ public:
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), CommandCompletions::eDiskFileCompletion,
         request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   }
 
   Options *GetOptions() override { return &m_option_group; }
diff --git a/lldb/source/Core/FormatEntity.cpp b/lldb/source/Core/FormatEntity.cpp
index 2257b7e..743c7c4 100644
--- a/lldb/source/Core/FormatEntity.cpp
+++ b/lldb/source/Core/FormatEntity.cpp
@@ -2350,7 +2350,6 @@ size_t FormatEntity::AutoComplete(CompletionRequest &request) {
 
   request.SetWordComplete(false);
   str = str.drop_front(request.GetMatchStartPoint());
-  request.GetMatches().Clear();
 
   const size_t dollar_pos = str.rfind('$');
   if (dollar_pos == llvm::StringRef::npos)
@@ -2360,7 +2359,7 @@ size_t FormatEntity::AutoComplete(CompletionRequest &request) {
   if (dollar_pos == str.size() - 1) {
     std::string match = str.str();
     match.append("{");
-    request.GetMatches().AppendString(match);
+    request.AddCompletion(match);
     return 1;
   }
 
@@ -2378,8 +2377,10 @@ size_t FormatEntity::AutoComplete(CompletionRequest &request) {
   llvm::StringRef partial_variable(str.substr(dollar_pos + 2));
   if (partial_variable.empty()) {
     // Suggest all top level entites as we are just past "${"
-    AddMatches(&g_root, str, llvm::StringRef(), request.GetMatches());
-    return request.GetMatches().GetSize();
+    StringList new_matches;
+    AddMatches(&g_root, str, llvm::StringRef(), new_matches);
+    request.AddCompletions(new_matches);
+    return request.GetNumberOfMatches();
   }
 
   // We have a partially specified variable, find it
@@ -2395,19 +2396,23 @@ size_t FormatEntity::AutoComplete(CompletionRequest &request) {
     // Exact match
     if (n > 0) {
       // "${thread.info" <TAB>
-      request.GetMatches().AppendString(MakeMatch(str, "."));
+      request.AddCompletion(MakeMatch(str, "."));
     } else {
       // "${thread.id" <TAB>
-      request.GetMatches().AppendString(MakeMatch(str, "}"));
+      request.AddCompletion(MakeMatch(str, "}"));
       request.SetWordComplete(true);
     }
   } else if (remainder.equals(".")) {
     // "${thread." <TAB>
-    AddMatches(entry_def, str, llvm::StringRef(), request.GetMatches());
+    StringList new_matches;
+    AddMatches(entry_def, str, llvm::StringRef(), new_matches);
+    request.AddCompletions(new_matches);
   } else {
     // We have a partial match
     // "${thre" <TAB>
-    AddMatches(entry_def, str, remainder, request.GetMatches());
+    StringList new_matches;
+    AddMatches(entry_def, str, remainder, new_matches);
+    request.AddCompletions(new_matches);
   }
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
diff --git a/lldb/source/Core/IOHandler.cpp b/lldb/source/Core/IOHandler.cpp
index 8474e4b..e7ebeea 100644
--- a/lldb/source/Core/IOHandler.cpp
+++ b/lldb/source/Core/IOHandler.cpp
@@ -245,10 +245,10 @@ int IOHandlerDelegate::IOHandlerComplete(IOHandler &io_handler,
         io_handler.GetDebugger().GetCommandInterpreter(),
         CommandCompletions::eVariablePathCompletion, request, nullptr);
 
-    size_t num_matches = request.GetMatches().GetSize();
+    size_t num_matches = request.GetNumberOfMatches();
     if (num_matches > 0) {
       std::string common_prefix;
-      request.GetMatches().LongestCommonPrefix(common_prefix);
+      matches.LongestCommonPrefix(common_prefix);
       const size_t partial_name_len = request.GetCursorArgumentPrefix().size();
 
       // If we matched a unique single command, add a space... Only do this if
diff --git a/lldb/source/Interpreter/CommandInterpreter.cpp b/lldb/source/Interpreter/CommandInterpreter.cpp
index 4c8b654..76cb5f2 100644
--- a/lldb/source/Interpreter/CommandInterpreter.cpp
+++ b/lldb/source/Interpreter/CommandInterpreter.cpp
@@ -1703,7 +1703,6 @@ bool CommandInterpreter::HandleCommand(const char *command_line,
 }
 
 int CommandInterpreter::HandleCompletionMatches(CompletionRequest &request) {
-  auto &matches = request.GetMatches();
   int num_command_matches = 0;
   bool look_for_subcommand = false;
 
@@ -1713,30 +1712,34 @@ int CommandInterpreter::HandleCompletionMatches(CompletionRequest &request) {
   if (request.GetCursorIndex() == -1) {
     // We got nothing on the command line, so return the list of commands
     bool include_aliases = true;
+    StringList new_matches;
     num_command_matches =
-        GetCommandNamesMatchingPartialString("", include_aliases, matches);
+        GetCommandNamesMatchingPartialString("", include_aliases, new_matches);
+    request.AddCompletions(new_matches);
   } else if (request.GetCursorIndex() == 0) {
     // The cursor is in the first argument, so just do a lookup in the
     // dictionary.
+    StringList new_matches;
     CommandObject *cmd_obj = GetCommandObject(
-        request.GetParsedLine().GetArgumentAtIndex(0), &matches);
-    num_command_matches = matches.GetSize();
+        request.GetParsedLine().GetArgumentAtIndex(0), &new_matches);
 
     if (num_command_matches == 1 && cmd_obj && cmd_obj->IsMultiwordObject() &&
-        matches.GetStringAtIndex(0) != nullptr &&
+        new_matches.GetStringAtIndex(0) != nullptr &&
         strcmp(request.GetParsedLine().GetArgumentAtIndex(0),
-               matches.GetStringAtIndex(0)) == 0) {
+               new_matches.GetStringAtIndex(0)) == 0) {
       if (request.GetParsedLine().GetArgumentCount() == 1) {
         request.SetWordComplete(true);
       } else {
         look_for_subcommand = true;
         num_command_matches = 0;
-        matches.DeleteStringAtIndex(0);
+        new_matches.DeleteStringAtIndex(0);
         request.GetParsedLine().AppendArgument(llvm::StringRef());
         request.SetCursorIndex(request.GetCursorIndex() + 1);
         request.SetCursorCharPosition(0);
       }
     }
+    request.AddCompletions(new_matches);
+    num_command_matches = request.GetNumberOfMatches();
   }
 
   if (request.GetCursorIndex() > 0 || look_for_subcommand) {
@@ -1773,8 +1776,7 @@ int CommandInterpreter::HandleCompletion(
       return 0;
     else if (first_arg[0] == CommandHistory::g_repeat_char) {
       if (auto hist_str = m_command_history.FindString(first_arg)) {
-        request.GetMatches().Clear();
-        request.GetMatches().InsertStringAtIndex(0, *hist_str);
+        matches.InsertStringAtIndex(0, *hist_str);
         return -2;
       } else
         return 0;
@@ -1812,7 +1814,7 @@ int CommandInterpreter::HandleCompletion(
         common_prefix.push_back(quote_char);
       common_prefix.push_back(' ');
     }
-    request.GetMatches().InsertStringAtIndex(0, common_prefix.c_str());
+    matches.InsertStringAtIndex(0, common_prefix.c_str());
   }
   return num_command_matches;
 }
diff --git a/lldb/source/Interpreter/CommandObject.cpp b/lldb/source/Interpreter/CommandObject.cpp
index 07be913..324b0b5 100644
--- a/lldb/source/Interpreter/CommandObject.cpp
+++ b/lldb/source/Interpreter/CommandObject.cpp
@@ -267,7 +267,6 @@ int CommandObject::HandleCompletion(CompletionRequest &request) {
   if (WantsRawCommandString() && !WantsCompletion()) {
     // FIXME: Abstract telling the completion to insert the completion
     // character.
-    request.GetMatches().Clear();
     return -1;
   } else {
     // Can we do anything generic with the options?
@@ -282,7 +281,7 @@ int CommandObject::HandleCompletion(CompletionRequest &request) {
       bool handled_by_options = cur_options->HandleOptionCompletion(
           request, opt_element_vector, GetCommandInterpreter());
       if (handled_by_options)
-        return request.GetMatches().GetSize();
+        return request.GetNumberOfMatches();
     }
 
     // If we got here, the last word is not an option or an option argument.
diff --git a/lldb/source/Interpreter/CommandObjectRegexCommand.cpp b/lldb/source/Interpreter/CommandObjectRegexCommand.cpp
index f975c0e..ec89ad8 100644
--- a/lldb/source/Interpreter/CommandObjectRegexCommand.cpp
+++ b/lldb/source/Interpreter/CommandObjectRegexCommand.cpp
@@ -97,9 +97,8 @@ int CommandObjectRegexCommand::HandleCompletion(CompletionRequest &request) {
   if (m_completion_type_mask) {
     CommandCompletions::InvokeCommonCompletionCallbacks(
         GetCommandInterpreter(), m_completion_type_mask, request, nullptr);
-    return request.GetMatches().GetSize();
+    return request.GetNumberOfMatches();
   } else {
-    request.GetMatches().Clear();
     request.SetWordComplete(false);
   }
   return 0;
diff --git a/lldb/source/Interpreter/OptionValue.cpp b/lldb/source/Interpreter/OptionValue.cpp
index 2d7c69e..c3f363b 100644
--- a/lldb/source/Interpreter/OptionValue.cpp
+++ b/lldb/source/Interpreter/OptionValue.cpp
@@ -575,8 +575,7 @@ bool OptionValue::DumpQualifiedName(Stream &strm) const {
 size_t OptionValue::AutoComplete(CommandInterpreter &interpreter,
                                  CompletionRequest &request) {
   request.SetWordComplete(false);
-  request.GetMatches().Clear();
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
 
 Status OptionValue::SetValueFromString(llvm::StringRef value,
diff --git a/lldb/source/Interpreter/OptionValueArch.cpp b/lldb/source/Interpreter/OptionValueArch.cpp
index 3d08780..d4f1fcb 100644
--- a/lldb/source/Interpreter/OptionValueArch.cpp
+++ b/lldb/source/Interpreter/OptionValueArch.cpp
@@ -76,9 +76,8 @@ lldb::OptionValueSP OptionValueArch::DeepCopy() const {
 size_t OptionValueArch::AutoComplete(CommandInterpreter &interpreter,
                                      CompletionRequest &request) {
   request.SetWordComplete(false);
-  request.GetMatches().Clear();
   CommandCompletions::InvokeCommonCompletionCallbacks(
       interpreter, CommandCompletions::eArchitectureCompletion, request,
       nullptr);
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
diff --git a/lldb/source/Interpreter/OptionValueBoolean.cpp b/lldb/source/Interpreter/OptionValueBoolean.cpp
index 8a34079..94c774d 100644
--- a/lldb/source/Interpreter/OptionValueBoolean.cpp
+++ b/lldb/source/Interpreter/OptionValueBoolean.cpp
@@ -79,7 +79,6 @@ lldb::OptionValueSP OptionValueBoolean::DeepCopy() const {
 size_t OptionValueBoolean::AutoComplete(CommandInterpreter &interpreter,
                                         CompletionRequest &request) {
   request.SetWordComplete(false);
-  request.GetMatches().Clear();
   static const llvm::StringRef g_autocomplete_entries[] = {
       "true", "false", "on", "off", "yes", "no", "1", "0"};
 
@@ -91,7 +90,7 @@ size_t OptionValueBoolean::AutoComplete(CommandInterpreter &interpreter,
 
   for (auto entry : entries) {
     if (entry.startswith_lower(request.GetCursorArgumentPrefix()))
-      request.GetMatches().AppendString(entry);
+      request.AddCompletion(entry);
   }
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
diff --git a/lldb/source/Interpreter/OptionValueEnumeration.cpp b/lldb/source/Interpreter/OptionValueEnumeration.cpp
index e78618e..c7cbcab 100644
--- a/lldb/source/Interpreter/OptionValueEnumeration.cpp
+++ b/lldb/source/Interpreter/OptionValueEnumeration.cpp
@@ -112,20 +112,18 @@ lldb::OptionValueSP OptionValueEnumeration::DeepCopy() const {
 size_t OptionValueEnumeration::AutoComplete(CommandInterpreter &interpreter,
                                             CompletionRequest &request) {
   request.SetWordComplete(false);
-  request.GetMatches().Clear();
 
   const uint32_t num_enumerators = m_enumerations.GetSize();
   if (!request.GetCursorArgumentPrefix().empty()) {
     for (size_t i = 0; i < num_enumerators; ++i) {
       llvm::StringRef name = m_enumerations.GetCStringAtIndex(i).GetStringRef();
       if (name.startswith(request.GetCursorArgumentPrefix()))
-        request.GetMatches().AppendString(name);
+        request.AddCompletion(name);
     }
   } else {
     // only suggest "true" or "false" by default
     for (size_t i = 0; i < num_enumerators; ++i)
-      request.GetMatches().AppendString(
-          m_enumerations.GetCStringAtIndex(i).GetStringRef());
+      request.AddCompletion(m_enumerations.GetCStringAtIndex(i).GetStringRef());
   }
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
diff --git a/lldb/source/Interpreter/OptionValueFileSpec.cpp b/lldb/source/Interpreter/OptionValueFileSpec.cpp
index 18bfcd6..2b93628 100644
--- a/lldb/source/Interpreter/OptionValueFileSpec.cpp
+++ b/lldb/source/Interpreter/OptionValueFileSpec.cpp
@@ -102,10 +102,9 @@ lldb::OptionValueSP OptionValueFileSpec::DeepCopy() const {
 size_t OptionValueFileSpec::AutoComplete(CommandInterpreter &interpreter,
                                          CompletionRequest &request) {
   request.SetWordComplete(false);
-  request.GetMatches().Clear();
   CommandCompletions::InvokeCommonCompletionCallbacks(
       interpreter, m_completion_mask, request, nullptr);
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
 
 const lldb::DataBufferSP &OptionValueFileSpec::GetFileContents() {
diff --git a/lldb/source/Interpreter/OptionValueUUID.cpp b/lldb/source/Interpreter/OptionValueUUID.cpp
index 7fa1552..355e07b 100644
--- a/lldb/source/Interpreter/OptionValueUUID.cpp
+++ b/lldb/source/Interpreter/OptionValueUUID.cpp
@@ -70,7 +70,6 @@ lldb::OptionValueSP OptionValueUUID::DeepCopy() const {
 size_t OptionValueUUID::AutoComplete(CommandInterpreter &interpreter,
                                      CompletionRequest &request) {
   request.SetWordComplete(false);
-  request.GetMatches().Clear();
   ExecutionContext exe_ctx(interpreter.GetExecutionContext());
   Target *target = exe_ctx.GetTargetPtr();
   if (target) {
@@ -86,12 +85,12 @@ size_t OptionValueUUID::AutoComplete(CommandInterpreter &interpreter,
             llvm::ArrayRef<uint8_t> module_bytes = module_uuid.GetBytes();
             if (module_bytes.size() >= uuid_bytes.size() &&
                 module_bytes.take_front(uuid_bytes.size()).equals(uuid_bytes)) {
-              request.GetMatches().AppendString(module_uuid.GetAsString());
+              request.AddCompletion(module_uuid.GetAsString());
             }
           }
         }
       }
     }
   }
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
diff --git a/lldb/source/Interpreter/Options.cpp b/lldb/source/Interpreter/Options.cpp
index f475897..c9567e9 100644
--- a/lldb/source/Interpreter/Options.cpp
+++ b/lldb/source/Interpreter/Options.cpp
@@ -680,7 +680,7 @@ bool Options::HandleOptionCompletion(CompletionRequest &request,
           if (!def.short_option)
             continue;
           opt_str[1] = def.short_option;
-          request.GetMatches().AppendString(opt_str);
+          request.AddCompletion(opt_str);
         }
 
         return true;
@@ -692,7 +692,7 @@ bool Options::HandleOptionCompletion(CompletionRequest &request,
 
           full_name.erase(full_name.begin() + 2, full_name.end());
           full_name.append(def.long_option);
-          request.GetMatches().AppendString(full_name.c_str());
+          request.AddCompletion(full_name.c_str());
         }
         return true;
       } else if (opt_defs_index != OptionArgElement::eUnrecognizedArg) {
@@ -705,10 +705,10 @@ bool Options::HandleOptionCompletion(CompletionRequest &request,
             strcmp(opt_defs[opt_defs_index].long_option, cur_opt_str) != 0) {
           std::string full_name("--");
           full_name.append(opt_defs[opt_defs_index].long_option);
-          request.GetMatches().AppendString(full_name.c_str());
+          request.AddCompletion(full_name.c_str());
           return true;
         } else {
-          request.GetMatches().AppendString(request.GetCursorArgument());
+          request.AddCompletion(request.GetCursorArgument());
           return true;
         }
       } else {
@@ -728,17 +728,7 @@ bool Options::HandleOptionCompletion(CompletionRequest &request,
             if (strstr(def.long_option, cur_opt_str + 2) == def.long_option) {
               std::string full_name("--");
               full_name.append(def.long_option);
-              // The options definitions table has duplicates because of the
-              // way the grouping information is stored, so only add once.
-              bool duplicate = false;
-              for (size_t k = 0; k < request.GetMatches().GetSize(); k++) {
-                if (request.GetMatches().GetStringAtIndex(k) == full_name) {
-                  duplicate = true;
-                  break;
-                }
-              }
-              if (!duplicate)
-                request.GetMatches().AppendString(full_name.c_str());
+              request.AddCompletion(full_name.c_str());
             }
           }
         }
@@ -790,7 +780,7 @@ bool Options::HandleOptionArgumentCompletion(
     for (int i = 0; enum_values[i].string_value != nullptr; i++) {
       if (strstr(enum_values[i].string_value, match_string.c_str()) ==
           enum_values[i].string_value) {
-        request.GetMatches().AppendString(enum_values[i].string_value);
+        request.AddCompletion(enum_values[i].string_value);
         return_value = true;
       }
     }
diff --git a/lldb/source/Symbol/Variable.cpp b/lldb/source/Symbol/Variable.cpp
index 7eafef1..8e9cadc 100644
--- a/lldb/source/Symbol/Variable.cpp
+++ b/lldb/source/Symbol/Variable.cpp
@@ -760,9 +760,11 @@ size_t Variable::AutoComplete(const ExecutionContext &exe_ctx,
   CompilerType compiler_type;
 
   bool word_complete = false;
+  StringList matches;
   PrivateAutoComplete(exe_ctx.GetFramePtr(), request.GetCursorArgumentPrefix(),
-                      "", compiler_type, request.GetMatches(), word_complete);
+                      "", compiler_type, matches, word_complete);
   request.SetWordComplete(word_complete);
+  request.AddCompletions(matches);
 
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
diff --git a/lldb/source/Utility/ArchSpec.cpp b/lldb/source/Utility/ArchSpec.cpp
index 320f2d9..1c50c31 100644
--- a/lldb/source/Utility/ArchSpec.cpp
+++ b/lldb/source/Utility/ArchSpec.cpp
@@ -255,12 +255,14 @@ size_t ArchSpec::AutoComplete(CompletionRequest &request) {
     for (uint32_t i = 0; i < llvm::array_lengthof(g_core_definitions); ++i) {
       if (NameMatches(g_core_definitions[i].name, NameMatch::StartsWith,
                       request.GetCursorArgumentPrefix()))
-        request.GetMatches().AppendString(g_core_definitions[i].name);
+        request.AddCompletion(g_core_definitions[i].name);
     }
   } else {
-    ListSupportedArchNames(request.GetMatches());
+    StringList matches;
+    ListSupportedArchNames(matches);
+    request.AddCompletions(matches);
   }
-  return request.GetMatches().GetSize();
+  return request.GetNumberOfMatches();
 }
 
 #define CPU_ANY (UINT32_MAX)
diff --git a/lldb/source/Utility/CompletionRequest.cpp b/lldb/source/Utility/CompletionRequest.cpp
index 1b7697a..c88747e 100644
--- a/lldb/source/Utility/CompletionRequest.cpp
+++ b/lldb/source/Utility/CompletionRequest.cpp
@@ -20,6 +20,7 @@ CompletionRequest::CompletionRequest(llvm::StringRef command_line,
     : m_command(command_line), m_raw_cursor_pos(raw_cursor_pos),
       m_match_start_point(match_start_point),
       m_max_return_elements(max_return_elements), m_matches(&matches) {
+  matches.Clear();
 
   // We parse the argument up to the cursor, so the last argument in
   // parsed_line is the one containing the cursor, and the cursor is after the
diff --git a/lldb/unittests/Utility/CompletionRequestTest.cpp b/lldb/unittests/Utility/CompletionRequestTest.cpp
index 134bf51..58dfab0 100644
--- a/lldb/unittests/Utility/CompletionRequestTest.cpp
+++ b/lldb/unittests/Utility/CompletionRequestTest.cpp
@@ -34,7 +34,70 @@ TEST(CompletionRequest, Constructor) {
 
   EXPECT_EQ(request.GetPartialParsedLine().GetArgumentCount(), 2u);
   EXPECT_STREQ(request.GetPartialParsedLine().GetArgumentAtIndex(1), "b");
+}
+
+TEST(CompletionRequest, DuplicateFiltering) {
+  std::string command = "a bad c";
+  const unsigned cursor_pos = 3;
+  StringList matches;
+
+  CompletionRequest request(command, cursor_pos, 0, 0, matches);
+
+  EXPECT_EQ(0U, request.GetNumberOfMatches());
+
+  // Add foo twice
+  request.AddCompletion("foo");
+  EXPECT_EQ(1U, request.GetNumberOfMatches());
+  EXPECT_EQ(1U, matches.GetSize());
+  EXPECT_STREQ("foo", matches.GetStringAtIndex(0));
+
+  request.AddCompletion("foo");
+  EXPECT_EQ(1U, request.GetNumberOfMatches());
+  EXPECT_EQ(1U, matches.GetSize());
+  EXPECT_STREQ("foo", matches.GetStringAtIndex(0));
+
+  // Add bar twice
+  request.AddCompletion("bar");
+  EXPECT_EQ(2U, request.GetNumberOfMatches());
+  EXPECT_EQ(2U, matches.GetSize());
+  EXPECT_STREQ("foo", matches.GetStringAtIndex(0));
+  EXPECT_STREQ("bar", matches.GetStringAtIndex(1));
+
+  request.AddCompletion("bar");
+  EXPECT_EQ(2U, request.GetNumberOfMatches());
+  EXPECT_EQ(2U, matches.GetSize());
+  EXPECT_STREQ("foo", matches.GetStringAtIndex(0));
+  EXPECT_STREQ("bar", matches.GetStringAtIndex(1));
+
+  // Add foo again.
+  request.AddCompletion("foo");
+  EXPECT_EQ(2U, request.GetNumberOfMatches());
+  EXPECT_EQ(2U, matches.GetSize());
+  EXPECT_STREQ("foo", matches.GetStringAtIndex(0));
+  EXPECT_STREQ("bar", matches.GetStringAtIndex(1));
+
+  // Add something with an existing prefix
+  request.AddCompletion("foobar");
+  EXPECT_EQ(3U, request.GetNumberOfMatches());
+  EXPECT_EQ(3U, matches.GetSize());
+  EXPECT_STREQ("foo", matches.GetStringAtIndex(0));
+  EXPECT_STREQ("bar", matches.GetStringAtIndex(1));
+  EXPECT_STREQ("foobar", matches.GetStringAtIndex(2));
+}
+
+TEST(CompletionRequest, TestCompletionOwnership) {
+  std::string command = "a bad c";
+  const unsigned cursor_pos = 3;
+  StringList matches;
+
+  CompletionRequest request(command, cursor_pos, 0, 0, matches);
+
+  std::string Temporary = "bar";
+  request.AddCompletion(Temporary);
+  // Manipulate our completion. The request should have taken a copy, so that
+  // shouldn't influence anything.
+  Temporary[0] = 'f';
 
-  // This is the generated matches should be equal to our passed string list.
-  EXPECT_EQ(&request.GetMatches(), &matches);
+  EXPECT_EQ(1U, request.GetNumberOfMatches());
+  EXPECT_STREQ("bar", matches.GetStringAtIndex(0));
 }