Support capturing for cargo test (#127)

* allow logs to be captured for cargo test

README.md

@@ -52,7 +52,7 @@ Tests can use the `env_logger` crate to see log messages generated during that t
 log = "0.4.0"
 
 [dev-dependencies]
-env_logger = { version = "0.6.0", default-features = false }
+env_logger = "0.6.0"
 ```
 
 ```rust
@@ -69,16 +69,22 @@ mod tests {
     use super::*;
     extern crate env_logger;
 
+    fn init() {
+        let _ = env_logger::builder().is_test(true).try_init();
+    }
+
     #[test]
     fn it_adds_one() {
-        let _ = env_logger::try_init();
+        init();
+
         info!("can log from the test too");
         assert_eq!(3, add_one(2));
     }
 
     #[test]
     fn it_handles_negative_numbers() {
-        let _ = env_logger::try_init();
+        init();
+
         info!("logging from another test");
         assert_eq!(-7, add_one(-8));
     }

src/fmt/writer/mod.rs

@@ -70,21 +70,23 @@ impl Writer {
 pub(crate) struct Builder {
     target: Target,
     write_style: WriteStyle,
+    is_test: bool,
     built: bool,
 }
 
 impl Builder {
     /// Initialize the writer builder with defaults.
-    pub fn new() -> Self {
+    pub(crate) fn new() -> Self {
         Builder {
             target: Default::default(),
             write_style: Default::default(),
+            is_test: false,
             built: false,
         }
     }
 
     /// Set the target to write to.
-    pub fn target(&mut self, target: Target) -> &mut Self {
+    pub(crate) fn target(&mut self, target: Target) -> &mut Self {
         self.target = target;
         self
     }
@@ -94,18 +96,24 @@ impl Builder {
     /// See the [Disabling colors] section for more details.
     ///
     /// [Disabling colors]: ../index.html#disabling-colors
-    pub fn parse(&mut self, write_style: &str) -> &mut Self {
+    pub(crate) fn parse_write_style(&mut self, write_style: &str) -> &mut Self {
         self.write_style(parse_write_style(write_style))
     }
 
     /// Whether or not to print style characters when writing.
-    pub fn write_style(&mut self, write_style: WriteStyle) -> &mut Self {
+    pub(crate) fn write_style(&mut self, write_style: WriteStyle) -> &mut Self {
         self.write_style = write_style;
         self
     }
 
+    /// Whether or not to capture logs for `cargo test`.
+    pub(crate) fn is_test(&mut self, is_test: bool) -> &mut Self {
+        self.is_test = is_test;
+        self
+    }
+
     /// Build a terminal writer.
-    pub fn build(&mut self) -> Writer {
+    pub(crate) fn build(&mut self) -> Writer {
         assert!(!self.built, "attempt to re-use consumed builder");
         self.built = true;
 
@@ -124,8 +132,8 @@ impl Builder {
         };
 
         let writer = match self.target {
-            Target::Stderr => BufferWriter::stderr(color_choice),
-            Target::Stdout => BufferWriter::stdout(color_choice),
+            Target::Stderr => BufferWriter::stderr(self.is_test, color_choice),
+            Target::Stdout => BufferWriter::stdout(self.is_test, color_choice),
         };
 
         Writer {

src/fmt/writer/termcolor/extern_impl.rs

@@ -8,7 +8,7 @@ use log::Level;
 use termcolor::{self, ColorChoice, ColorSpec, WriteColor};
 
 use ::WriteStyle;
-use ::fmt::Formatter;
+use ::fmt::{Formatter, Target};
 
 pub(in ::fmt::writer) mod glob {
     pub use super::*;
@@ -69,51 +69,98 @@ impl Formatter {
     }
 }
 
-pub(in ::fmt::writer) struct BufferWriter(termcolor::BufferWriter);
-pub(in ::fmt) struct Buffer(termcolor::Buffer);
+pub(in ::fmt::writer) struct BufferWriter {
+    inner: termcolor::BufferWriter,
+    test_target: Option<Target>,
+}
+
+pub(in ::fmt) struct Buffer {
+    inner: termcolor::Buffer,
+    test_target: Option<Target>,
+}
 
 impl BufferWriter {
-    pub(in ::fmt::writer) fn stderr(write_style: WriteStyle) -> Self {
-        BufferWriter(termcolor::BufferWriter::stderr(write_style.into_color_choice()))
+    pub(in ::fmt::writer) fn stderr(is_test: bool, write_style: WriteStyle) -> Self {
+        BufferWriter {
+            inner: termcolor::BufferWriter::stderr(write_style.into_color_choice()),
+            test_target: if is_test {
+                Some(Target::Stderr)
+            } else {
+                None
+            },
+        }
     }
 
-    pub(in ::fmt::writer) fn stdout(write_style: WriteStyle) -> Self {
-        BufferWriter(termcolor::BufferWriter::stdout(write_style.into_color_choice()))
+    pub(in ::fmt::writer) fn stdout(is_test: bool, write_style: WriteStyle) -> Self {
+        BufferWriter {
+            inner: termcolor::BufferWriter::stdout(write_style.into_color_choice()),
+            test_target: if is_test {
+                Some(Target::Stdout)
+            } else {
+                None
+            },
+        }
     }
 
     pub(in ::fmt::writer) fn buffer(&self) -> Buffer {
-        Buffer(self.0.buffer())
+        Buffer {
+            inner: self.inner.buffer(),
+            test_target: self.test_target,
+        }
     }
 
     pub(in ::fmt::writer) fn print(&self, buf: &Buffer) -> io::Result<()> {
-        self.0.print(&buf.0)
+        if let Some(target) = self.test_target {
+            // This impl uses the `eprint` and `print` macros
+            // instead of `termcolor`'s buffer.
+            // This is so their output can be captured by `cargo test`
+            let log = String::from_utf8_lossy(buf.bytes());
+
+            match target {
+                Target::Stderr => eprint!("{}", log),
+                Target::Stdout => print!("{}", log),
+            }
+
+            Ok(())
+        } else {
+            self.inner.print(&buf.inner)
+        }
     }
 }
 
 impl Buffer {
     pub(in ::fmt) fn clear(&mut self) {
-        self.0.clear()
+        self.inner.clear()
     }
 
     pub(in ::fmt) fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        self.0.write(buf)
+        self.inner.write(buf)
     }
 
     pub(in ::fmt) fn flush(&mut self) -> io::Result<()> {
-        self.0.flush()
+        self.inner.flush()
     }
 
-    #[cfg(test)]
     pub(in ::fmt) fn bytes(&self) -> &[u8] {
-        self.0.as_slice()
+        self.inner.as_slice()
     }
 
     fn set_color(&mut self, spec: &ColorSpec) -> io::Result<()> {
-        self.0.set_color(spec)
+        // Ignore styles for test captured logs because they can't be printed
+        if self.test_target.is_none() {
+            self.inner.set_color(spec)
+        } else {
+            Ok(())
+        }
     }
 
     fn reset(&mut self) -> io::Result<()> {
-        self.0.reset()
+        // Ignore styles for test captured logs because they can't be printed
+        if self.test_target.is_none() {
+            self.inner.reset()
+        } else {
+            Ok(())
+        }
     }
 }
 

src/fmt/writer/termcolor/shim_impl.rs

@@ -13,13 +13,13 @@ pub(in ::fmt::writer) struct BufferWriter {
 pub(in ::fmt) struct Buffer(Vec<u8>);
 
 impl BufferWriter {
-    pub(in ::fmt::writer) fn stderr(_: WriteStyle) -> Self {
+    pub(in ::fmt::writer) fn stderr(_is_test: bool, _write_style: WriteStyle) -> Self {
         BufferWriter {
             target: Target::Stderr,
         }
     }
 
-    pub(in ::fmt::writer) fn stdout(_: WriteStyle) -> Self {
+    pub(in ::fmt::writer) fn stdout(_is_test: bool, _write_style: WriteStyle) -> Self {
         BufferWriter {
             target: Target::Stdout,
         }

src/lib.rs

@@ -139,6 +139,33 @@
 //! * `error,hello=warn/[0-9]scopes` turn on global error logging and also
 //!   warn for hello. In both cases the log message must include a single digit
 //!   number followed by 'scopes'.
+//! 
+//! ## Capturing logs in tests
+//! 
+//! Records logged during `cargo test` will not be captured by the test harness by default.
+//! The [`Builder::is_test`] method can be used in unit tests to ensure logs will be captured:
+//! 
+//! ```
+//! # #[macro_use] extern crate log;
+//! # extern crate env_logger;
+//! # fn main() {}
+//! #[cfg(test)]
+//! mod tests {
+//!     fn init() {
+//!         let _ = env_logger::builder().is_test(true).try_init();
+//!     }
+//! 
+//!     #[test]
+//!     fn it_works() {
+//!         info!("This record will be captured by `cargo test`");
+//! 
+//!         assert_eq!(2, 1 + 1);
+//!     }
+//! }
+//! ```
+//! 
+//! Enabling test capturing comes at the expense of color and other style support
+//! and may have performance implications.
 //!
 //! ## Disabling colors
 //!
@@ -157,9 +184,7 @@
 //! The following example excludes the timestamp from the log output:
 //! 
 //! ```
-//! use env_logger::Builder;
-//!
-//! Builder::from_default_env()
+//! env_logger::builder()
 //!     .default_format_timestamp(false)
 //!     .init();
 //! ```
@@ -180,9 +205,8 @@
 //! 
 //! ```
 //! use std::io::Write;
-//! use env_logger::Builder;
 //!
-//! Builder::from_default_env()
+//! env_logger::builder()
 //!     .format(|buf, record| {
 //!         writeln!(buf, "{}: {}", record.level(), record.args())
 //!     })
@@ -199,13 +223,14 @@
 //! isn't set:
 //! 
 //! ```
-//! use env_logger::{Builder, Env};
+//! use env_logger::Env;
 //!
-//! Builder::from_env(Env::default().default_filter_or("warn")).init();
+//! env_logger::from_env(Env::default().default_filter_or("warn")).init();
 //! ```
 //! 
 //! [log-crate-url]: https://docs.rs/log/
 //! [`Builder`]: struct.Builder.html
+//! [`Builder::is_test`]: struct.Builder.html#method.is_test
 //! [`Env`]: struct.Env.html
 //! [`fmt`]: fmt/index.html
 
@@ -404,7 +429,7 @@ impl Builder {
         let env = env.into();
 
         if let Some(s) = env.get_filter() {
-            builder.parse(&s);
+            builder.parse_filters(&s);
         }
 
         if let Some(s) = env.get_write_style() {
@@ -579,7 +604,16 @@ impl Builder {
     /// environment variable.
     ///
     /// See the module documentation for more details.
+    #[deprecated(since = "0.6.0", note = "use `parse_filters` instead.")]
     pub fn parse(&mut self, filters: &str) -> &mut Self {
+        self.parse_filters(filters)
+    }
+
+    /// Parses the directives string in the same form as the `RUST_LOG`
+    /// environment variable.
+    ///
+    /// See the module documentation for more details.
+    pub fn parse_filters(&mut self, filters: &str) -> &mut Self {
         self.filter.parse(filters);
         self
     }
@@ -630,7 +664,16 @@ impl Builder {
     ///
     /// See the module documentation for more details.
     pub fn parse_write_style(&mut self, write_style: &str) -> &mut Self {
-        self.writer.parse(write_style);
+        self.writer.parse_write_style(write_style);
+        self
+    }
+
+    /// Sets whether or not the logger will be used in unit tests.
+    /// 
+    /// If `is_test` is `true` then the logger will allow the testing framework to
+    /// capture log records rather than printing them to the terminal directly.
+    pub fn is_test(&mut self, is_test: bool) -> &mut Self {
+        self.writer.is_test(is_test);
         self
     }
 
@@ -1068,6 +1111,23 @@ where
     try_init_from_env(env).expect("env_logger::init_from_env should not be called after logger initialized");
 }
 
+/// Create a new builder with the default environment variables.
+/// 
+/// The builder can be configured before being initialized.
+pub fn builder() -> Builder {
+    Builder::from_default_env()
+}
+
+/// Create a builder from the given environment variables.
+/// 
+/// The builder can be configured before being initialized.
+pub fn from_env<'a, E>(env: E) -> Builder
+where
+    E: Into<Env<'a>>
+{
+    Builder::from_env(env)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

tests/init-twice-retains-filter.rs

@@ -15,7 +15,7 @@ fn main() {
         // Init again using a different max level
         // This shouldn't clobber the level that was previously set
         env_logger::Builder::new()
-            .parse("info")
+            .parse_filters("info")
             .try_init()
             .unwrap_err();