Overhauls the logging system

Updated fmt to 8.0.0.
This is now more compile-time, and outputs to stderr, file as well as a buffer.

src/common/logging/log.cpp

@@ -3,9 +3,20 @@
 // Refer to the license.txt file included.
 
 #include <chrono>
+#include <cstdio>
+#ifdef _WIN32
+#include <share.h> // For _SH_DENYWR
+#else
+#define _SH_DENYWR 0
+#endif
+
+#include "common/common_paths.h"
+#include "common/file_util.h"
 #include "common/logging/log.h"
 #include "common/string_util.h"
 
+namespace Common::Logging {
+
 std::uint64_t GetLoggingTime() {
     static auto time_origin = std::chrono::steady_clock::now();
     return std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now() -
@@ -13,6 +24,38 @@ std::uint64_t GetLoggingTime() {
         .count();
 }
 
-std::string StandardizeLogClass(const std::string& log_class) {
-    return Common::ReplaceAll(log_class, "_", ".");
+// _SH_DENYWR allows read-only access for other programs. For non-Windows it's defined to 0.
+static FileUtil::IOFile g_log_file{LOG_FILE, "w", _SH_DENYWR};
+
+static std::array<Entry, 3> g_error_buffer{};
+static int g_error_buffer_pos = 0;
+
+void WriteLog(Entry entry) {
+    // stderr
+    fmt::print(stderr, entry.style, entry.message);
+
+    // log file
+    g_log_file.WriteString(entry.message);
+    if (entry.level >= Level::Error) {
+        g_log_file.Flush(); // Do not flush the file too often
+    }
+
+    // log buffer
+    if (entry.level >= Level::Error) {
+        g_error_buffer[g_error_buffer_pos] = std::move(entry);
+        g_error_buffer_pos = (g_error_buffer_pos + 1) % g_error_buffer.size();
+    }
 }
+
+std::string GetLastErrors() {
+    std::string output;
+    for (std::size_t i = 0; i < g_error_buffer.size(); ++i) {
+        const std::size_t pos = (g_error_buffer_pos + i) % g_error_buffer.size();
+        if (g_error_buffer[pos].level != Level::Invalid) {
+            output.append(g_error_buffer[pos].message);
+        }
+    }
+    return output;
+}
+
+} // namespace Common::Logging