completion: delete insertText; don't set filterText if it is the same as label

It decreases Content-Length: from 32K to 25K for the following case:

 #include <bits/stdc++.h>
int main() { std::| }

Also

* make results deterministic when completion text is empty
* sort by newText, label, filterText

src/message_handler.hh

@@ -119,10 +119,9 @@ struct CompletionItem {
   std::string label;
   CompletionItemKind kind = CompletionItemKind::Text;
   std::string detail;
-  std::optional<std::string> documentation;
+  std::string documentation;
   std::string sortText;
-  std::optional<std::string> filterText;
-  std::string insertText;
+  std::string filterText;
   InsertTextFormat insertTextFormat = InsertTextFormat::PlainText;
   TextEdit textEdit;
   std::vector<TextEdit> additionalTextEdits;

src/messages/textDocument_completion.cc

@@ -34,9 +34,23 @@ using namespace llvm;
 
 MAKE_REFLECT_TYPE_PROXY(InsertTextFormat);
 MAKE_REFLECT_TYPE_PROXY(CompletionItemKind);
-MAKE_REFLECT_STRUCT(CompletionItem, label, kind, detail, documentation,
-                    sortText, filterText, insertText, insertTextFormat,
-                    textEdit, additionalTextEdits);
+
+void Reflect(Writer &vis, CompletionItem &v) {
+  REFLECT_MEMBER_START();
+  REFLECT_MEMBER(label);
+  REFLECT_MEMBER(kind);
+  REFLECT_MEMBER(detail);
+  if (v.documentation.size())
+    REFLECT_MEMBER(documentation);
+  REFLECT_MEMBER(sortText);
+  if (v.filterText.size())
+    REFLECT_MEMBER(filterText);
+  REFLECT_MEMBER(insertTextFormat);
+  REFLECT_MEMBER(textEdit);
+  if (v.additionalTextEdits.size())
+    REFLECT_MEMBER(additionalTextEdits);
+  REFLECT_MEMBER_END();
+}
 
 namespace {
 struct CompletionList {
@@ -67,7 +81,6 @@ void DecorateIncludePaths(const std::smatch &match,
     item.textEdit.newText =
         prefix + quote0 + item.textEdit.newText + quote1 + suffix;
     item.label = prefix + quote0 + item.label + quote1 + suffix;
-    item.filterText = std::nullopt;
   }
 }
 
@@ -124,8 +137,8 @@ void FilterCandidates(CompletionList &result, const std::string &complete_text,
     std::string sort(4, ' ');
     for (auto &item : items) {
       item.textEdit.range = lsRange{begin_pos, end_pos};
-      if (has_open_paren && item.filterText)
-        item.textEdit.newText = *item.filterText;
+      if (has_open_paren)
+        item.textEdit.newText = item.filterText;
       // https://github.com/Microsoft/language-server-protocol/issues/543
       // Order of textEdit and additionalTextEdits is unspecified.
       auto &edits = item.additionalTextEdits;
@@ -133,48 +146,44 @@ void FilterCandidates(CompletionList &result, const std::string &complete_text,
         Position start = edits[0].range.start, end = edits[0].range.end;
         item.textEdit.range.start = start;
         item.textEdit.newText = edits[0].newText + item.textEdit.newText;
-        if (start.line == begin_pos.line && item.filterText) {
+        if (start.line == begin_pos.line) {
           item.filterText =
               buffer_line.substr(start.character,
                                  end.character - start.character) +
-              *item.filterText;
+              item.filterText;
         }
         edits.erase(edits.begin());
       }
+      if (item.filterText == item.label)
+        item.filterText.clear();
       for (auto i = sort.size(); i && ++sort[i - 1] == 'A';)
         sort[--i] = ' ';
       item.sortText = sort;
-      // Compatibility
-      item.insertText = item.textEdit.newText;
     }
   };
 
-  // No complete text; don't run any filtering logic except to trim the items.
-  if (!g_config->completion.filterAndSort || complete_text.empty()) {
+  if (!g_config->completion.filterAndSort) {
     finalize();
     return;
   }
 
-  // Make sure all items have |filterText| set, code that follow needs it.
-  for (auto &item : items) {
-    if (!item.filterText)
-      item.filterText = item.label;
+  if (complete_text.size()) {
+    // Fuzzy match and remove awful candidates.
+    bool sensitive = g_config->completion.caseSensitivity;
+    FuzzyMatcher fuzzy(complete_text, sensitive);
+    for (CompletionItem &item : items) {
+      const std::string &filter =
+          item.filterText.size() ? item.filterText : item.label;
+      item.score_ = ReverseSubseqMatch(complete_text, filter, sensitive) >= 0
+                        ? fuzzy.Match(filter)
+                        : FuzzyMatcher::kMinScore;
+    }
+    items.erase(std::remove_if(items.begin(), items.end(),
+                               [](const CompletionItem &item) {
+                                 return item.score_ <= FuzzyMatcher::kMinScore;
+                               }),
+                items.end());
   }
-
-  // Fuzzy match and remove awful candidates.
-  bool sensitive = g_config->completion.caseSensitivity;
-  FuzzyMatcher fuzzy(complete_text, sensitive);
-  for (auto &item : items) {
-    item.score_ =
-        ReverseSubseqMatch(complete_text, *item.filterText, sensitive) >= 0
-            ? fuzzy.Match(*item.filterText)
-            : FuzzyMatcher::kMinScore;
-  }
-  items.erase(std::remove_if(items.begin(), items.end(),
-                             [](const CompletionItem &item) {
-                               return item.score_ <= FuzzyMatcher::kMinScore;
-                             }),
-              items.end());
   std::sort(items.begin(), items.end(),
             [](const CompletionItem &lhs, const CompletionItem &rhs) {
               int t = int(lhs.additionalTextEdits.size() -
@@ -185,9 +194,13 @@ void FilterCandidates(CompletionList &result, const std::string &complete_text,
                 return lhs.score_ > rhs.score_;
               if (lhs.priority_ != rhs.priority_)
                 return lhs.priority_ < rhs.priority_;
-              if (lhs.filterText->size() != rhs.filterText->size())
-                return lhs.filterText->size() < rhs.filterText->size();
-              return *lhs.filterText < *rhs.filterText;
+              t = lhs.textEdit.newText.compare(rhs.textEdit.newText);
+              if (t)
+                return t < 0;
+              t = lhs.label.compare(rhs.label);
+              if (t)
+                return t < 0;
+              return lhs.filterText < rhs.filterText;
             });
 
   // Trim result.
@@ -293,8 +306,7 @@ void BuildItem(const CodeCompletionResult &R, const CodeCompletionString &CCS,
     case CodeCompletionString::CK_TypedText:
       text = Chunk.Text;
       for (auto i = first; i < out.size(); i++)
-        if (Kind == CodeCompletionString::CK_TypedText && !out[i].filterText)
-          out[i].filterText = text;
+        out[i].filterText = text;
       break;
     case CodeCompletionString::CK_Placeholder:
       text = Chunk.Text;
@@ -414,7 +426,7 @@ public:
         ls_items[j].priority_ = CCS->getPriority();
         if (!g_config->completion.detailedLabel) {
           ls_items[j].detail = ls_items[j].label;
-          ls_items[j].label = ls_items[j].filterText.value_or("");
+          ls_items[j].label = ls_items[j].filterText;
         }
       }
 #if LLVM_VERSION_MAJOR >= 7