util: Properly handle errors during log message formatting

Instead of having an exception propagate into the program when an
error happens while formatting a log message, just print a message to
the log.

Addresses #9423.

src/util.h

@@ -73,14 +73,24 @@ bool LogAcceptCategory(const char* category);
 /** Send a string to the log output */
 int LogPrintStr(const std::string &str);
 
-#define LogPrint(category, ...) do { \
-    if (LogAcceptCategory((category))) { \
-        LogPrintStr(tfm::format(__VA_ARGS__)); \
+/** Get format string from VA_ARGS for error reporting */
+template<typename... Args> std::string FormatStringFromLogArgs(const char *fmt, const Args&... args) { return fmt; }
+
+#define LogPrintf(...) do { \
+    std::string _log_msg_; /* Unlikely name to avoid shadowing variables */ \
+    try { \
+        _log_msg_ = tfm::format(__VA_ARGS__); \
+    } catch (std::runtime_error &e) { \
+        /* Original format string will have newline so don't add one here */ \
+        _log_msg_ = "Error \"" + std::string(e.what()) + "\" while formatting log message: " + FormatStringFromLogArgs(__VA_ARGS__); \
     } \
+    LogPrintStr(_log_msg_); \
 } while(0)
 
-#define LogPrintf(...) do { \
-    LogPrintStr(tfm::format(__VA_ARGS__)); \
+#define LogPrint(category, ...) do { \
+    if (LogAcceptCategory((category))) { \
+        LogPrintf(__VA_ARGS__); \
+    } \
 } while(0)
 
 template<typename... Args>