explicitly call TString::MutRef in the conversion to std::string (#28207)

Hide implementation and use move constructor.
IGNIETFERRO-2155

Author: ubyte

ydb/public/sdk/cpp/include/ydb-cpp-sdk/library/issue/yql_issue.h

@@ -3,7 +3,6 @@
 #include <util/generic/ptr.h>
 #include <util/generic/yexception.h>
 #include <util/stream/output.h>
-#include <util/stream/str.h>
 #include <util/system/types.h>
 #include <util/str_stl.h>
 
@@ -183,11 +182,7 @@ class TIssue: public TThrRefBase {
 
     void PrintTo(IOutputStream& out, bool oneLine = false) const;
 
-    std::string ToString(bool oneLine = false) const {
-        TStringStream out;
-        PrintTo(out, oneLine);
-        return out.Str();
-    }
+    std::string ToString(bool oneLine = false) const;
 
     // Unsafe method. Doesn't call SanitizeNonAscii(Message)
     std::string* MutableMessage() {
@@ -295,11 +290,7 @@ class TIssues {
             const std::string& programFilename,
             const std::string& programText) const;
 
-    inline std::string ToString(bool oneLine = false) const {
-        TStringStream out;
-        PrintTo(out, oneLine);
-        return out.Str();
-    }
+    std::string ToString(bool oneLine = false) const;
 
     std::string ToOneLineString() const {
         return ToString(true);

ydb/public/sdk/cpp/src/library/issue/yql_issue.cpp

@@ -7,6 +7,7 @@
 #include <library/cpp/colorizer/output.h>
 
 #include <util/charset/utf8.h>
+#include <util/stream/str.h>
 #include <util/string/ascii.h>
 #include <util/string/split.h>
 #include <util/string/strip.h>
@@ -79,6 +80,12 @@ void TIssue::PrintTo(IOutputStream& out, bool oneLine) const {
     }
 }
 
+std::string TIssue::ToString(bool oneLine) const {
+    TStringStream out;
+    PrintTo(out, oneLine);
+    return std::move(out.Str().MutRef());
+}
+
 void WalkThroughIssues(const TIssue& topIssue, bool leafOnly, std::function<void(const TIssue&, uint16_t level)> fn, std::function<void(const TIssue&, uint16_t level)> afterChildrenFn) {
     enum class EFnType {
         Main,
@@ -224,6 +231,12 @@ void TIssues::PrintWithProgramTo(
     }
 }
 
+std::string TIssues::ToString(bool oneLine) const {
+    TStringStream out;
+    PrintTo(out, oneLine);
+    return std::move(out.Str().MutRef());
+}
+
 TIssue ExceptionToIssue(const std::exception& e, const TPosition& pos) {
     std::string_view messageBuf = e.what();
     auto parsedPos = TryParseTerminationMessage(messageBuf);