CBL-7125: c4Log sometimes does not log anything (#2302)

Refactor c4log_writeToCallback and c4log_setCallbackLevel so that they function independently of each other. In particular, calling setCallbackLevel with LevelNone won't remove the default logCallback. The new behavior matches with that of the pair of writeToBinary and setBinaryFileLevel.

Author: jianminzhao

C/c4Log.cc

@@ -184,17 +184,17 @@ static bool           sDefaultLogCallbackPreformatted;
 
 // LCOV_EXCL_START
 void c4log_writeToCallback(C4LogLevel level, C4LogCallback callback, bool preformatted) noexcept {
-    if ( !callback ) level = kC4LogNone;
+    if ( !callback ) return;
+
     if ( sDefaultLogCallback ) {
         c4log_removeObserver(sDefaultLogCallback);
         c4logobserver_release(sDefaultLogCallback);
         sDefaultLogCallback = nullptr;
     }
-    if ( level != kC4LogNone ) {
-        auto obs = make_retained<LogCallback>(callback, preformatted);
-        LogObserver::add(obs, LogLevel(level));
-        sDefaultLogCallback = toExternal(std::move(obs));
-    }
+    auto obs = make_retained<LogCallback>(callback, preformatted);
+    LogObserver::add(obs, LogLevel(level));
+    sDefaultLogCallback = toExternal(std::move(obs));
+
     sDefaultLogCallbackLevel        = level;
     sDefaultLogCallbackPreformatted = preformatted;
 }
@@ -204,8 +204,14 @@ C4LogCallback c4log_getCallback() noexcept { return sDefaultLogCallbackFn; }
 C4LogLevel c4log_callbackLevel() noexcept { return sDefaultLogCallbackLevel; }  // LCOV_EXCL_LINE
 
 void c4log_setCallbackLevel(C4LogLevel level) noexcept {
-    if ( level != sDefaultLogCallbackLevel && sDefaultLogCallback )
-        c4log_writeToCallback(level, sDefaultLogCallbackFn, sDefaultLogCallbackPreformatted);
+    if ( level != sDefaultLogCallbackLevel && sDefaultLogCallback ) {
+        if ( level == kC4LogNone ) c4log_removeObserver(sDefaultLogCallback);
+        else {
+            auto logCallback = toInternal(sDefaultLogCallback);
+            LogObserver::remove(logCallback);
+            LogObserver::add(logCallback, LogLevel(level));
+        }
+    }
     sDefaultLogCallbackLevel = level;
 }
 
@@ -270,10 +276,9 @@ C4LogLevel c4log_binaryFileLevel() noexcept { return sDefaultLogFilesLevel; }
 
 void c4log_setBinaryFileLevel(C4LogLevel level) noexcept {
     if ( sDefaultLogFiles && level != sDefaultLogFilesLevel ) {
-        if ( level == kC4LogNone ) {
-            if ( sDefaultLogFiles ) { c4log_removeObserver(sDefaultLogFiles); }
-        } else {
-            auto logFiles = dynamic_cast<LogFiles*>(toInternal(sDefaultLogFiles));
+        if ( level == kC4LogNone ) c4log_removeObserver(sDefaultLogFiles);
+        else {
+            auto logFiles = toInternal(sDefaultLogFiles);
             LogObserver::remove(logFiles);
             LogObserver::add(logFiles, LogLevel(level));
         }