[lldb] returning command completions up to a maximum

- Adding `max_return_elements` field to `CompletionRequest`.
- adding maximum checks to `SymbolCompleter` and `SourceFileCompleter`.

Author: eronnen

lldb/include/lldb/Utility/CompletionRequest.h

@@ -115,6 +115,11 @@ class CompletionRequest {
   CompletionRequest(llvm::StringRef command_line, unsigned raw_cursor_pos,
                     CompletionResult &result);
 
+  /// Sets the maximum number of completions that should be returned.
+  void SetMaxReturnElements(size_t max_return_elements) {
+    m_max_return_elements = max_return_elements;
+  }
+
   /// Returns the raw user input used to create this CompletionRequest cut off
   /// at the cursor position. The cursor will be at the end of the raw line.
   llvm::StringRef GetRawLine() const {
@@ -157,6 +162,23 @@ class CompletionRequest {
 
   size_t GetCursorIndex() const { return m_cursor_index; }
 
+  size_t GetMaxReturnElements() const { return m_max_return_elements; }
+
+  /// Returns true if the maximum number of completions has been reached
+  /// already.
+  bool ShouldStopAddingResults() const {
+    return m_result.GetNumberOfResults() >= m_max_return_elements;
+  }
+
+  /// Returns the maximum number of completions that need to be added
+  /// until reaching the maximum
+  size_t GetMaxNumberOfResultsToAdd() const {
+    const size_t number_of_results = m_result.GetNumberOfResults();
+    if (number_of_results >= m_max_return_elements)
+      return 0;
+    return m_max_return_elements - number_of_results;
+  }
+
   /// 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
@@ -231,6 +253,8 @@ class CompletionRequest {
   size_t m_cursor_index;
   /// The cursor position in the argument indexed by m_cursor_index.
   size_t m_cursor_char_position;
+  /// The maximum number of completions that should be returned.
+  size_t m_max_return_elements = SIZE_MAX;
 
   /// The result this request is supposed to fill out.
   /// We keep this object private to ensure that no backend can in any way

lldb/source/API/SBCommandInterpreter.cpp

@@ -266,6 +266,8 @@ int SBCommandInterpreter::HandleCompletionWithDescriptions(
   lldb_private::StringList lldb_matches, lldb_descriptions;
   CompletionResult result;
   CompletionRequest request(current_line, cursor - current_line, result);
+  if (max_return_elements >= 0)
+    request.SetMaxReturnElements(max_return_elements);
   m_opaque_ptr->HandleCompletion(request);
   result.GetMatches(lldb_matches);
   result.GetDescriptions(lldb_descriptions);

lldb/source/Commands/CommandCompletions.cpp

@@ -91,7 +91,7 @@ bool CommandCompletions::InvokeCommonCompletionCallbacks(
        nullptr} // This one has to be last in the list.
   };
 
-  for (int i = 0;; i++) {
+  for (int i = 0; !request.ShouldStopAddingResults(); i++) {
     if (common_completions[i].type == lldb::eTerminatorCompletion)
       break;
     else if ((common_completions[i].type & completion_mask) ==
@@ -167,7 +167,9 @@ class SourceFileCompleter : public Completer {
         m_matching_files.AppendIfUnique(context.comp_unit->GetPrimaryFile());
       }
     }
-    return Searcher::eCallbackReturnContinue;
+    return m_matching_files.GetSize() >= m_request.GetMaxNumberOfResultsToAdd()
+               ? Searcher::eCallbackReturnStop
+               : Searcher::eCallbackReturnContinue;
   }
 
   void DoCompletion(SearchFilter *filter) override {
@@ -230,6 +232,10 @@ class SymbolCompleter : public Completer {
 
       // Now add the functions & symbols to the list - only add if unique:
       for (const SymbolContext &sc : sc_list) {
+        if (m_match_set.size() >= m_request.GetMaxNumberOfResultsToAdd()) {
+          break;
+        }
+
         ConstString func_name = sc.GetFunctionName(Mangled::ePreferDemangled);
         // Ensure that the function name matches the regex. This is more than
         // a sanity check. It is possible that the demangled function name
@@ -239,7 +245,9 @@ class SymbolCompleter : public Completer {
           m_match_set.insert(func_name);
       }
     }
-    return Searcher::eCallbackReturnContinue;
+    return m_match_set.size() >= m_request.GetMaxNumberOfResultsToAdd()
+               ? Searcher::eCallbackReturnStop
+               : Searcher::eCallbackReturnContinue;
   }
 
   void DoCompletion(SearchFilter *filter) override {