Pre-filter completion results before sending to vscode.

This results in a less laggy completion experience. Before, vscode would
drop frames if handed too many completions (ie, by typing #include in a
very large project).

src/command_line.cc

@@ -435,11 +435,53 @@ void EmitDiagnostics(WorkingFiles* working_files, std::string path, NonElidedVec
   });
 }
 
+// Pre-filters completion responses before sending to vscode. This results in a
+// significantly snappier completion experience as vscode is easily overloaded
+// when given 1000+ completion items.
+void FilterCompletionResponse(Out_TextDocumentComplete* complete_response,
+                              const std::string& complete_text) {
+  // Used to inject more completions.
+#if false
+  const size_t kNumIterations = 250;
+  size_t size = complete_response->result.items.size();
+  complete_response->result.items.reserve(size * (kNumIterations + 1));
+  for (size_t iteration = 0; iteration < kNumIterations; ++iteration) {
+    for (size_t i = 0; i < size; ++i) {
+      auto item = complete_response->result.items[i];
+      item.label += "#" + std::to_string(iteration);
+      complete_response->result.items.push_back(item);
+    }
+  }
+#endif
 
 
+  const size_t kMaxResultSize = 100u;
+  if (complete_response->result.items.size() > kMaxResultSize) {
+    //std::cerr << "!!! Filtering " << complete_response->result.items.size() << " results using " << complete_text << std::endl;
 
+    complete_response->result.isIncomplete = true;
 
+    if (complete_text.empty()) {
+      complete_response->result.items.resize(kMaxResultSize);
+    }
+    else {
+      NonElidedVector<lsCompletionItem> filtered_result;
+      filtered_result.reserve(kMaxResultSize);
+      for (const lsCompletionItem& item : complete_response->result.items) {
+        if (SubstringMatch(complete_text, item.label)) {
+          //std::cerr << "!! emitting " << item.label << std::endl;
+          filtered_result.push_back(item);
+          if (filtered_result.size() >= kMaxResultSize)
+            break;
+        }
+      }
 
+      complete_response->result.items = filtered_result;
+    }
+
+    //std::cerr << "!! Filtering resulted in " << complete_response->result.items.size() << " entries" << std::endl;
+  }
+}
 
 
 
@@ -1547,15 +1589,20 @@ bool QueryDbMainLoop(
           }
 
           std::cerr << "[complete] Returning " << complete_response.result.items.size() << " include completions" << std::endl;
+          FilterCompletionResponse(&complete_response, buffer_line);
           ipc->SendOutMessageToClient(IpcId::TextDocumentCompletion, complete_response);
         }
         else {
           bool is_global_completion = false;
-          if (file)
-            msg->params.position = file->FindStableCompletionSource(msg->params.position, &is_global_completion);
+          std::string existing_completion;
+          if (file) {
+            msg->params.position = file->FindStableCompletionSource(msg->params.position, &is_global_completion, &existing_completion);
+          }
+
+          std::cerr << "[complete] Got existing completion " << existing_completion;
 
           ClangCompleteManager::OnComplete callback = std::bind(
-            [working_files, global_code_complete_cache, non_global_code_complete_cache, is_global_completion]
+            [working_files, global_code_complete_cache, non_global_code_complete_cache, is_global_completion, existing_completion]
             (Ipc_TextDocumentComplete* msg, NonElidedVector<lsCompletionItem> results) {
 
             Out_TextDocumentComplete complete_response;
@@ -1564,6 +1611,7 @@ bool QueryDbMainLoop(
             complete_response.result.items = results;
 
             // Emit completion results.
+            FilterCompletionResponse(&complete_response, existing_completion);
             IpcManager::instance()->SendOutMessageToClient(IpcId::TextDocumentCompletion, complete_response);
 
             // Cache completion results.

src/lex_utils.cc

@@ -1,5 +1,7 @@
 #include "lex_utils.h"
 
+#include <doctest/doctest.h>
+
 int GetOffsetForPosition(lsPosition position, const std::string& content) {
   int offset = 0;
 
@@ -173,4 +175,65 @@ std::string LexWordAroundPos(lsPosition position, const std::string& content) {
   }
 
   return content.substr(start, end - start + 1);
-}
+}
+
+bool SubstringMatch(const std::string& search, const std::string& content) {
+  if (search.empty())
+    return true;
+
+  size_t search_index = 0;
+  char search_char = tolower(search[search_index]);
+
+  size_t content_index = 0;
+
+  while (true) {
+    char content_char = tolower(content[content_index]);
+
+    if (content_char == search_char) {
+      search_index += 1;
+      if (search_index >= search.size())
+        return true;
+      search_char = tolower(search[search_index]);
+    }
+
+    content_index += 1;
+    if (content_index >= content.size())
+      return false;
+  }
+
+  return false;
+}
+
+TEST_SUITE("Substring");
+
+TEST_CASE("match") {
+  // Sanity.
+  REQUIRE(SubstringMatch("a", "aa"));
+  REQUIRE(SubstringMatch("aa", "aa"));
+
+  // Empty string matches anything.
+  REQUIRE(SubstringMatch("", ""));
+  REQUIRE(SubstringMatch("", "aa"));
+
+  // Match in start/middle/end.
+  REQUIRE(SubstringMatch("a", "abbbb"));
+  REQUIRE(SubstringMatch("a", "bbabb"));
+  REQUIRE(SubstringMatch("a", "bbbba"));
+  REQUIRE(SubstringMatch("aa", "aabbb"));
+  REQUIRE(SubstringMatch("aa", "bbaab"));
+  REQUIRE(SubstringMatch("aa", "bbbaa"));
+
+  // Capitalization.
+  REQUIRE(SubstringMatch("aa", "aA"));
+  REQUIRE(SubstringMatch("aa", "Aa"));
+  REQUIRE(SubstringMatch("aa", "AA"));
+
+  // Token skipping.
+  REQUIRE(SubstringMatch("ad", "abcd"));
+  REQUIRE(SubstringMatch("ad", "ABCD"));
+
+  // Ordering.
+  REQUIRE(!SubstringMatch("ad", "dcba"));
+}
+
+TEST_SUITE_END();

src/lex_utils.h

@@ -17,4 +17,6 @@ optional<lsRange> ExtractQuotedRange(int line_number, const std::string& line);
 
 void LexFunctionDeclaration(const std::string& buffer_content, lsPosition declaration_spelling, optional<std::string> type_name, std::string* insert_text, int* newlines_after_name);
 
-std::string LexWordAroundPos(lsPosition position, const std::string& content);
+std::string LexWordAroundPos(lsPosition position, const std::string& content);
+
+bool SubstringMatch(const std::string& search, const std::string& content);

src/working_files.cc

@@ -214,12 +214,11 @@ std::string WorkingFile::FindClosestCallNameInBuffer(lsPosition position, int* a
   return buffer_content.substr(offset, start_offset - offset + 1);
 }
 
-// Returns a position which contains the most recent ., ->, :, or ( for code
-// completion purposes.
-lsPosition WorkingFile::FindStableCompletionSource(lsPosition position, bool* is_global_completion) const {
+lsPosition WorkingFile::FindStableCompletionSource(lsPosition position, bool* is_global_completion, std::string* existing_completion) const {
   *is_global_completion = true;
 
-  int offset = GetOffsetForPosition(position, buffer_content);
+  int start_offset = GetOffsetForPosition(position, buffer_content);
+  int offset = start_offset;
 
   while (offset > 0) {
     char c = buffer_content[offset - 1];
@@ -241,6 +240,7 @@ lsPosition WorkingFile::FindStableCompletionSource(lsPosition position, bool* is
     --offset;
   }
 
+  *existing_completion = buffer_content.substr(offset, start_offset - offset);
   return GetPositionForOffset(buffer_content, offset);
 }
 
@@ -403,4 +403,21 @@ TEST_CASE("auto-insert )") {
   REQUIRE(active_param == 0);
 }
 
+TEST_CASE("existing completion") {
+  WorkingFile f("foo.cc", "zzz.asdf");
+  bool is_global_completion;
+  std::string existing_completion;
+
+  f.FindStableCompletionSource(CharPos(f, '.'), &is_global_completion, &existing_completion);
+  REQUIRE(existing_completion == "zzz");
+  f.FindStableCompletionSource(CharPos(f, 'a', 1), &is_global_completion, &existing_completion);
+  REQUIRE(existing_completion == "a");
+  f.FindStableCompletionSource(CharPos(f, 's', 1), &is_global_completion, &existing_completion);
+  REQUIRE(existing_completion == "as");
+  f.FindStableCompletionSource(CharPos(f, 'd', 1), &is_global_completion, &existing_completion);
+  REQUIRE(existing_completion == "asd");
+  f.FindStableCompletionSource(CharPos(f, 'f', 1), &is_global_completion, &existing_completion);
+  REQUIRE(existing_completion == "asdf");
+}
+
 TEST_SUITE_END();

src/working_files.h

@@ -61,7 +61,9 @@ struct WorkingFile {
   //
   // The out param |is_global_completion| is set to true if this looks like a
   // global completion.
-  lsPosition FindStableCompletionSource(lsPosition position, bool* is_global_completion) const;
+  // The out param |existing_completion| is set to any existing completion
+  // content the user has entered.
+  lsPosition FindStableCompletionSource(lsPosition position, bool* is_global_completion, std::string* existing_completion) const;
 
   CXUnsavedFile AsUnsavedFile() const;
 };