Make llvm::StringRef to std::string conversions explicit.

This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.

This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.

This doesn't actually modify StringRef yet, I'll do that in a follow-up.

Author: d0k

clang-tools-extra/clang-change-namespace/ChangeNamespace.cpp

@@ -23,7 +23,7 @@ inline std::string
 joinNamespaces(const llvm::SmallVectorImpl<StringRef> &Namespaces) {
   if (Namespaces.empty())
     return "";
-  std::string Result = Namespaces.front();
+  std::string Result(Namespaces.front());
   for (auto I = Namespaces.begin() + 1, E = Namespaces.end(); I != E; ++I)
     Result += ("::" + *I).str();
   return Result;
@@ -184,7 +184,7 @@ void addReplacementOrDie(
     const SourceManager &SM,
     std::map<std::string, tooling::Replacements> *FileToReplacements) {
   const auto R = createReplacement(Start, End, ReplacementText, SM);
-  auto Err = (*FileToReplacements)[R.getFilePath()].add(R);
+  auto Err = (*FileToReplacements)[std::string(R.getFilePath())].add(R);
   if (Err)
     llvm_unreachable(llvm::toString(std::move(Err)).c_str());
 }
@@ -213,18 +213,18 @@ std::string getShortestQualifiedNameInNamespace(llvm::StringRef DeclName,
   DeclName = DeclName.ltrim(':');
   NsName = NsName.ltrim(':');
   if (DeclName.find(':') == llvm::StringRef::npos)
-    return DeclName;
+    return std::string(DeclName);
 
   auto NsNameSplitted = splitSymbolName(NsName);
   auto DeclNsSplitted = splitSymbolName(DeclName);
   llvm::StringRef UnqualifiedDeclName = DeclNsSplitted.pop_back_val();
   // If the Decl is in global namespace, there is no need to shorten it.
   if (DeclNsSplitted.empty())
-    return UnqualifiedDeclName;
+    return std::string(UnqualifiedDeclName);
   // If NsName is the global namespace, we can simply use the DeclName sans
   // leading "::".
   if (NsNameSplitted.empty())
-    return DeclName;
+    return std::string(DeclName);
 
   if (NsNameSplitted.front() != DeclNsSplitted.front()) {
     // The DeclName must be fully-qualified, but we still need to decide if a
@@ -233,7 +233,7 @@ std::string getShortestQualifiedNameInNamespace(llvm::StringRef DeclName,
     // to avoid conflict.
     if (llvm::is_contained(NsNameSplitted, DeclNsSplitted.front()))
       return ("::" + DeclName).str();
-    return DeclName;
+    return std::string(DeclName);
   }
   // Since there is already an overlap namespace, we know that `DeclName` can be
   // shortened, so we reduce the longest common prefix.
@@ -711,7 +711,7 @@ void ChangeNamespaceTool::moveOldNamespace(
   MoveNs.InsertionOffset = SM.getFileOffset(SM.getSpellingLoc(InsertionLoc));
   MoveNs.FID = SM.getFileID(Start);
   MoveNs.SourceMgr = Result.SourceManager;
-  MoveNamespaces[SM.getFilename(Start)].push_back(MoveNs);
+  MoveNamespaces[std::string(SM.getFilename(Start))].push_back(MoveNs);
 }
 
 // Removes a class forward declaration from the code in the moved namespace and
@@ -762,7 +762,7 @@ void ChangeNamespaceTool::moveClassForwardDeclaration(
   InsertForwardDeclaration InsertFwd;
   InsertFwd.InsertionOffset = Insertion.getOffset();
   InsertFwd.ForwardDeclText = Insertion.getReplacementText().str();
-  InsertFwdDecls[Insertion.getFilePath()].push_back(InsertFwd);
+  InsertFwdDecls[std::string(Insertion.getFilePath())].push_back(InsertFwd);
 }
 
 // Replaces a qualified symbol (in \p DeclCtx) that refers to a declaration \p
@@ -816,7 +816,7 @@ void ChangeNamespaceTool::replaceQualifiedSymbolInDeclContext(
                                           ->getQualifiedNameAsString())) {
       FromDeclNameRef = FromDeclNameRef.drop_front(2);
       if (FromDeclNameRef.size() < ReplaceName.size())
-        ReplaceName = FromDeclNameRef;
+        ReplaceName = std::string(FromDeclNameRef);
     }
   }
   // Checks if there is any namespace alias declarations that can shorten the

clang-tools-extra/clang-change-namespace/tool/ClangChangeNamespace.cpp

@@ -91,7 +91,7 @@ llvm::ErrorOr<std::vector<std::string>> GetWhiteListedSymbolPatterns() {
   llvm::StringRef Content = File.get()->getBuffer();
   Content.split(Lines, '\n', /*MaxSplit=*/-1, /*KeepEmpty=*/false);
   for (auto Line : Lines)
-    Patterns.push_back(Line.trim());
+    Patterns.push_back(std::string(Line.trim()));
   return Patterns;
 }