Allow building a Logger yourself (#53)

* make logger build public

* ensure logger keeps printed records consistent

Author: KodrAus

examples/direct_logger.rs

@@ -0,0 +1,40 @@
+/*!
+Using `env_logger::Logger` and the `log::Log` trait directly.
+
+This example doesn't rely on environment variables, or having a static logger installed.
+*/
+
+extern crate log;
+extern crate env_logger;
+
+fn record() -> log::Record<'static> {
+    let error_metadata = log::MetadataBuilder::new()
+        .target("myApp")
+        .level(log::Level::Error)
+        .build();
+
+    log::Record::builder()
+        .metadata(error_metadata)
+        .args(format_args!("Error!"))
+        .line(Some(433))
+        .file(Some("app.rs"))
+        .module_path(Some("server"))
+        .build()
+}
+
+fn main() {
+    use log::Log;
+
+    let stylish_logger = env_logger::Builder::new()
+        .filter(None, log::LevelFilter::Error)
+        .write_style(env_logger::WriteStyle::Always)
+        .build();
+
+    let unstylish_logger = env_logger::Builder::new()
+        .filter(None, log::LevelFilter::Error)
+        .write_style(env_logger::WriteStyle::Never)
+        .build();
+    
+    stylish_logger.log(&record());
+    unstylish_logger.log(&record());
+}

src/fmt.rs

@@ -67,6 +67,7 @@ pub use termcolor::Color;
 /// [`style`]: #method.style
 pub struct Formatter {
     buf: Rc<RefCell<Buffer>>,
+    write_style: WriteStyle,
 }
 
 /// A set of styles to apply to the terminal output.
@@ -179,7 +180,16 @@ impl Default for WriteStyle {
 }
 
 /// A terminal target with color awareness.
-pub(crate) struct Writer(BufferWriter);
+pub(crate) struct Writer {
+    inner: BufferWriter,
+    write_style: WriteStyle,
+}
+
+impl Writer {
+    pub(crate) fn write_style(&self) -> WriteStyle {
+        self.write_style
+    }
+}
 
 /// A builder for a terminal writer.
 /// 
@@ -232,7 +242,10 @@ impl Builder {
             Target::Stdout => BufferWriter::stdout(color_choice),
         };
 
-        Writer(writer)
+        Writer {
+            inner: writer,
+            write_style: self.write_style,
+        }
     }
 }
 
@@ -355,10 +368,15 @@ impl Style {
 impl Formatter {
     pub(crate) fn new(writer: &Writer) -> Self {
         Formatter {
-            buf: Rc::new(RefCell::new(writer.0.buffer())),
+            buf: Rc::new(RefCell::new(writer.inner.buffer())),
+            write_style: writer.write_style(),
         }
     }
 
+    pub(crate) fn write_style(&self) -> WriteStyle {
+        self.write_style
+    }
+
     /// Begin a new [`Style`].
     /// 
     /// # Examples
@@ -414,7 +432,7 @@ impl Formatter {
     }
 
     pub(crate) fn print(&self, writer: &Writer) -> io::Result<()> {
-        writer.0.print(&self.buf.borrow())
+        writer.inner.print(&self.buf.borrow())
     }
 
     pub(crate) fn clear(&mut self) {

src/lib.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! A simple logger configured via an environment variable which writes 
+//! A simple logger configured via environment variables which writes 
 //! to stdout or stderr, for use with the logging facade exposed by the
 //! [`log` crate][log-crate-url].
 //!
@@ -426,7 +426,7 @@ impl Builder {
     /// This method is kept private because the only way we support building
     /// loggers is by installing them as the single global logger for the
     /// `log` crate.
-    fn build(&mut self) -> Logger {
+    pub fn build(&mut self) -> Logger {
         Logger {
             writer: self.writer.build(),
             filter: self.filter.build(),
@@ -460,11 +460,9 @@ impl Log for Logger {
             // so will always at least have capacity for the largest log record formatted
             // on that thread.
             // 
-            // Because these buffers are tied to a particular logger, we don't let callers
-            // create instances of `Logger` themselves, or they'll race to configure the
-            // thread local buffer with their own configuration. This is still potentially
-            // an issue if a caller attempts to set and use the global logger multiple times,
-            // but in that case it's clearer that there's shared state at play.
+            // If multiple `Logger`s are used by the same threads then the thread-local
+            // formatter might have different color support. If this is the case the
+            // formatter and its buffer are discarded and recreated.
 
             thread_local! {
                 static FORMATTER: RefCell<Option<Formatter>> = RefCell::new(None);
@@ -473,8 +471,15 @@ impl Log for Logger {
             FORMATTER.with(|tl_buf| {
                 let mut tl_buf = tl_buf.borrow_mut();
 
-                if tl_buf.is_none() {
-                    *tl_buf = Some(Formatter::new(&self.writer));
+                // Check the buffer style. If it's different from the logger's 
+                // style then drop the buffer and recreate it.
+                match *tl_buf {
+                    Some(ref mut formatter) => {
+                        if formatter.write_style() != self.writer.write_style() {
+                            *formatter = Formatter::new(&self.writer)
+                        }
+                    },
+                    ref mut tl_buf => *tl_buf = Some(Formatter::new(&self.writer))
                 }
 
                 // The format is guaranteed to be `Some` by this point