fs/io/BufferedReader: count line numbers

Replaces the dirty code in config/ConfigFile.cxx.

src/fs/io/BufferedReader.cxx

@@ -59,8 +59,10 @@ BufferedReader::ReadLine()
 {
 	do {
 		char *line = ReadBufferedLine(buffer);
-		if (line != nullptr)
+		if (line != nullptr) {
+			++line_number;
 			return line;
+		}
 	} while (Fill(true));
 
 	if (last_error.IsDefined() || !eof || buffer.IsEmpty())
@@ -78,5 +80,6 @@ BufferedReader::ReadLine()
 
 	char *line = buffer.Read().data;
 	buffer.Clear();
+	++line_number;
 	return line;
 }

src/fs/io/BufferedReader.hxx

@@ -41,9 +41,12 @@ class BufferedReader {
 
 	bool eof;
 
+	unsigned line_number;
+
 public:
 	BufferedReader(Reader &_reader)
-		:reader(_reader), buffer(4096), eof(false) {}
+		:reader(_reader), buffer(4096), eof(false),
+		 line_number(0) {}
 
 	gcc_pure
 	bool Check() const {
@@ -70,6 +73,10 @@ public:
 	}
 
 	char *ReadLine();
+
+	unsigned GetLineNumber() const {
+		return line_number;
+	}
 };
 
 #endif