Add BuildWithCustomFormat trait

src/build.rs

@@ -1,4 +1,6 @@
-use slog::Logger;
+use slog::{Drain, Logger};
+use slog_term::Decorator;
+use std::fmt::Debug;
 
 use file::FileLoggerBuilder;
 use null::NullLoggerBuilder;
@@ -11,6 +13,16 @@ pub trait Build {
     fn build(&self) -> Result<Logger>;
 }
 
+pub trait BuildWithCustomFormat {
+    type Decorator: Decorator;
+
+    fn build_with_custom_format<F, D>(&self, f: F) -> Result<Logger>
+    where
+        F: FnOnce(Self::Decorator) -> Result<D>,
+        D: Drain + Send + 'static,
+        D::Err: Debug;
+}
+
 /// Logger builder.
 #[derive(Debug)]
 #[allow(clippy::large_enum_variant)]

src/file.rs

@@ -16,7 +16,7 @@ use std::time::{Duration, Instant};
 use misc::{module_and_line, timezone_to_timestamp_fn};
 use types::KVFilterParameters;
 use types::{Format, OverflowStrategy, Severity, SourceLocation, TimeZone};
-use {Build, Config, ErrorKind, Result};
+use {Build, BuildWithCustomFormat, Config, ErrorKind, Result};
 
 /// A logger builder which build loggers that write log records to the specified file.
 ///
@@ -197,9 +197,23 @@ impl Build for FileLoggerBuilder {
         Ok(logger)
     }
 }
+impl BuildWithCustomFormat for FileLoggerBuilder {
+    type Decorator = PlainDecorator<FileAppender>;
+
+    fn build_with_custom_format<F, D>(&self, f: F) -> Result<Logger>
+    where
+        F: FnOnce(Self::Decorator) -> Result<D>,
+        D: Drain + Send + 'static,
+        D::Err: Debug,
+    {
+        let decorator = PlainDecorator::new(self.appender.clone());
+        let drain = track!(f(decorator))?;
+        Ok(self.build_with_drain(drain))
+    }
+}
 
 #[derive(Debug)]
-struct FileAppender {
+pub struct FileAppender {
     path: PathBuf,
     file: Option<BufWriter<File>>,
     truncate: bool,

src/lib.rs

@@ -64,7 +64,7 @@ extern crate tempfile;
 extern crate trackable;
 extern crate regex;
 
-pub use build::{Build, LoggerBuilder};
+pub use build::{Build, BuildWithCustomFormat, LoggerBuilder};
 pub use config::{Config, LoggerConfig};
 pub use error::{Error, ErrorKind};
 pub use misc::set_stdlog_logger;

src/terminal.rs

@@ -9,7 +9,7 @@ use std::io;
 use misc::{module_and_line, timezone_to_timestamp_fn};
 use types::KVFilterParameters;
 use types::{Format, OverflowStrategy, Severity, SourceLocation, TimeZone};
-use {Build, Config, Result};
+use {Build, BuildWithCustomFormat, Config, Result};
 
 /// A logger builder which build loggers that output log records to the terminal.
 ///
@@ -151,6 +151,20 @@ impl Build for TerminalLoggerBuilder {
         Ok(logger)
     }
 }
+impl BuildWithCustomFormat for TerminalLoggerBuilder {
+    type Decorator = Decorator;
+
+    fn build_with_custom_format<F, D>(&self, f: F) -> Result<Logger>
+    where
+        F: FnOnce(Self::Decorator) -> Result<D>,
+        D: Drain + Send + 'static,
+        D::Err: Debug,
+    {
+        let decorator = self.destination.to_decorator();
+        let drain = track!(f(decorator))?;
+        Ok(self.build_with_drain(drain))
+    }
+}
 
 /// The destination to which log records will be outputted.
 ///
@@ -192,7 +206,7 @@ impl Destination {
     }
 }
 
-enum Decorator {
+pub enum Decorator {
     Term(TermDecorator),
     PlainStdout(PlainDecorator<io::Stdout>),
     PlainStderr(PlainDecorator<io::Stderr>),