Fix race condition in client suggestions

base/common/LineReader.cpp

@@ -38,10 +38,10 @@ bool hasInputData()
 
 }
 
-LineReader::Suggest::WordsRange LineReader::Suggest::getCompletions(const String & prefix, size_t prefix_length) const
+std::optional<LineReader::Suggest::WordsRange> LineReader::Suggest::getCompletions(const String & prefix, size_t prefix_length) const
 {
     if (!ready)
-        return std::make_pair(words.end(), words.end());
+        return std::nullopt;
 
     std::string_view last_word;
 

base/common/LineReader.h

@@ -4,6 +4,7 @@
 
 #include <atomic>
 #include <vector>
+#include <optional>
 
 class LineReader
 {
@@ -18,7 +19,7 @@ public:
         std::atomic<bool> ready{false};
 
         /// Get iterators for the matched range of words if any.
-        WordsRange getCompletions(const String & prefix, size_t prefix_length) const;
+        std::optional<WordsRange> getCompletions(const String & prefix, size_t prefix_length) const;
     };
 
     using Patterns = std::vector<const char *>;

base/common/ReadlineLineReader.cpp

@@ -30,7 +30,8 @@ static LineReader::Suggest::Words::const_iterator end;
 static void findRange(const char * prefix, size_t prefix_length)
 {
     std::string prefix_str(prefix);
-    std::tie(pos, end) = suggest->getCompletions(prefix_str, prefix_length);
+    if (auto completions = suggest->getCompletions(prefix_str, prefix_length))
+        std::tie(pos, end) = *completions;
 }
 
 /// Iterates through matched range.

base/common/ReplxxLineReader.cpp

@@ -70,8 +70,9 @@ ReplxxLineReader::ReplxxLineReader(
 
     auto callback = [&suggest] (const String & context, size_t context_size)
     {
-        auto range = suggest.getCompletions(context, context_size);
-        return Replxx::completions_t(range.first, range.second);
+        if (auto range = suggest.getCompletions(context, context_size))
+            return Replxx::completions_t(range->first, range->second);
+        return Replxx::completions_t();
     };
 
     rx.set_completion_callback(callback);