Revert "lib/fs: Put the caseFS as the outermost layer (#9648)"

This reverts commit 7517d18fbb.

Fixes #9677

lib/fs/filesystem.go

@@ -261,6 +261,11 @@ func NewFilesystem(fsType FilesystemType, uri string, opts ...Option) Filesystem
 		}
 	}
 
+	// Case handling is the innermost, as any filesystem calls by wrappers should be case-resolved
+	if caseOpt != nil {
+		fs = caseOpt.apply(fs)
+	}
+
 	// mtime handling should happen inside walking, as filesystem calls while
 	// walking should be mtime-resolved too
 	if mtimeOpt != nil {
@@ -269,35 +274,15 @@ func NewFilesystem(fsType FilesystemType, uri string, opts ...Option) Filesystem
 
 	fs = &metricsFS{next: fs}
 
-	layersAboveWalkFilesystem := 0
-	if caseOpt != nil {
-		// DirNames calls made to check the case of a name will also be
-		// attributed to the calling function.
-		layersAboveWalkFilesystem++
-	}
 	if l.ShouldDebug("walkfs") {
-		// A walkFilesystem is not a layer to skip, it embeds the underlying
-		// filesystem, passing calls directly trough. Except for calls made
-		// during walking, however those are truly originating in the walk
-		// filesystem.
-		fs = NewWalkFilesystem(newLogFilesystem(fs, layersAboveWalkFilesystem))
-	} else if l.ShouldDebug("fs") {
-		fs = newLogFilesystem(NewWalkFilesystem(fs), layersAboveWalkFilesystem)
-	} else {
-		fs = NewWalkFilesystem(fs)
+		return NewWalkFilesystem(&logFilesystem{fs})
 	}
 
-	// Case handling is at the outermost layer to resolve all input names.
-	// Reason being is that the only names/paths that are potentially "wrong"
-	// come from outside the fs package. Any paths that result from filesystem
-	// operations itself already have the correct case. Thus there's e.g. no
-	// point to check the case on all the stating the walk filesystem does, it
-	// just adds overhead.
-	if caseOpt != nil {
-		fs = caseOpt.apply(fs)
+	if l.ShouldDebug("fs") {
+		return &logFilesystem{NewWalkFilesystem(fs)}
 	}
 
-	return fs
+	return NewWalkFilesystem(fs)
 }
 
 // IsInternal returns true if the file, as a path relative to the folder