5 files changed, 11 insertions, 19 deletions

diff --git a/lldb/include/lldb/Utility/StringList.h b/lldb/include/lldb/Utility/StringList.h
index 68c1f87510f..22b5b2c3b09 100644
--- a/lldb/include/lldb/Utility/StringList.h
+++ b/lldb/include/lldb/Utility/StringList.h
@@ -69,7 +69,7 @@ public:
 
   void Clear();
 
-  void LongestCommonPrefix(std::string &common_prefix);
+  std::string LongestCommonPrefix();
 
   void InsertStringAtIndex(size_t idx, const std::string &str);
 
diff --git a/lldb/source/Core/IOHandler.cpp b/lldb/source/Core/IOHandler.cpp
index 203b9e8af07..51cae59639f 100644
--- a/lldb/source/Core/IOHandler.cpp
+++ b/lldb/source/Core/IOHandler.cpp
@@ -243,8 +243,7 @@ int IOHandlerDelegate::IOHandlerComplete(
 
     size_t num_matches = request.GetNumberOfMatches();
     if (num_matches > 0) {
-      std::string common_prefix;
-      matches.LongestCommonPrefix(common_prefix);
+      std::string common_prefix = matches.LongestCommonPrefix();
       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 379251b0276..2bc41621af5 100644
--- a/lldb/source/Interpreter/CommandInterpreter.cpp
+++ b/lldb/source/Interpreter/CommandInterpreter.cpp
@@ -1857,8 +1857,7 @@ int CommandInterpreter::HandleCompletion(
     // element 0, otherwise put an empty string in element 0.
     std::string command_partial_str = request.GetCursorArgumentPrefix().str();
 
-    std::string common_prefix;
-    matches.LongestCommonPrefix(common_prefix);
+    std::string common_prefix = matches.LongestCommonPrefix();
     const size_t partial_name_len = command_partial_str.size();
     common_prefix.erase(0, partial_name_len);
 
diff --git a/lldb/source/Utility/StringList.cpp b/lldb/source/Utility/StringList.cpp
index fb0d9be8797..03249e00ccc 100644
--- a/lldb/source/Utility/StringList.cpp
+++ b/lldb/source/Utility/StringList.cpp
@@ -100,10 +100,9 @@ void StringList::Join(const char *separator, Stream &strm) {
 
 void StringList::Clear() { m_strings.clear(); }
 
-void StringList::LongestCommonPrefix(std::string &common_prefix) {
-  common_prefix.clear();
+std::string StringList::LongestCommonPrefix() {
   if (m_strings.empty())
-    return;
+    return {};
 
   auto args = llvm::makeArrayRef(m_strings);
   llvm::StringRef prefix = args.front();
@@ -115,7 +114,7 @@ void StringList::LongestCommonPrefix(std::string &common_prefix) {
     }
     prefix = prefix.take_front(count);
   }
-  common_prefix = prefix;
+  return prefix.str();
 }
 
 void StringList::InsertStringAtIndex(size_t idx, const char *str) {
diff --git a/lldb/unittests/Utility/StringListTest.cpp b/lldb/unittests/Utility/StringListTest.cpp
index 7d62631bb8e..a0890800861 100644
--- a/lldb/unittests/Utility/StringListTest.cpp
+++ b/lldb/unittests/Utility/StringListTest.cpp
@@ -214,8 +214,7 @@ TEST(StringListTest, SplitIntoLinesEmpty) {
 
 TEST(StringListTest, LongestCommonPrefixEmpty) {
   StringList s;
-  std::string prefix = "this should be cleared";
-  s.LongestCommonPrefix(prefix);
+  std::string prefix = s.LongestCommonPrefix();
   EXPECT_EQ("", prefix);
 }
 
@@ -226,8 +225,7 @@ TEST(StringListTest, LongestCommonPrefix) {
   s.AppendString("foo");
   s.AppendString("foozar");
 
-  std::string prefix = "this should be cleared";
-  s.LongestCommonPrefix(prefix);
+  std::string prefix = s.LongestCommonPrefix();
   EXPECT_EQ("foo", prefix);
 }
 
@@ -235,8 +233,7 @@ TEST(StringListTest, LongestCommonPrefixSingleElement) {
   StringList s;
   s.AppendString("foo");
 
-  std::string prefix = "this should be cleared";
-  s.LongestCommonPrefix(prefix);
+  std::string prefix = s.LongestCommonPrefix();
   EXPECT_EQ("foo", prefix);
 }
 
@@ -245,8 +242,7 @@ TEST(StringListTest, LongestCommonPrefixDuplicateElement) {
   s.AppendString("foo");
   s.AppendString("foo");
 
-  std::string prefix = "this should be cleared";
-  s.LongestCommonPrefix(prefix);
+  std::string prefix = s.LongestCommonPrefix();
   EXPECT_EQ("foo", prefix);
 }
 
@@ -257,8 +253,7 @@ TEST(StringListTest, LongestCommonPrefixNoPrefix) {
   s.AppendString("2foo");
   s.AppendString("3foozar");
 
-  std::string prefix = "this should be cleared";
-  s.LongestCommonPrefix(prefix);
+  std::string prefix = s.LongestCommonPrefix();
   EXPECT_EQ("", prefix);
 }