Change Log


0.4.11 - 2020-07-09


  • Support coercing structured values into concrete types.
  • Reference the win_dbg_logger in the readme.


  • Updates a few deprecated items used internally.
  • Fixed issues in docs and expands sections.
  • Show the correct build badge in the readme.
  • Fix up a possible inference breakage with structured value errors.
  • Respect formatting flags in structured value formatting.

0.4.10 - 2019-12-16 (yanked)


  • Fixed the log! macros so they work in expression context (this regressed in 0.4.9, which has been yanked).

0.4.9 - 2019-12-12 (yanked)

Minimum Supported Rust Version

This release bumps the minimum compiler version to 1.31.0. This was mainly needed for cfg-if, but between 1.16.0 and 1.31.0 there are a lot of language and library improvements we now take advantage of.


  • Unstable support for capturing key-value pairs in a record using the log! macros


  • Better documentation for max level filters.
  • Internal updates to line up with bumped MSRV

0.4.8 - 2019-07-28


  • Support attempting to get Record fields as static strings.

0.4.7 - 2019-07-06


  • Support for embedded environments with thread-unsafe initialization.
  • Initial unstable support for capturing structured data under the kv_unstable feature gate. This new API doesn't affect existing users and may change in future patches (so those changes may not appear in the changelog until it stabilizes).


  • Docs for using log with the 2018 edition.
  • Error messages for macros missing arguments.

0.4.6 - 2018-10-27


  • Support 2018-style macro import for the log_enabled! macro.

0.4.5 - 2018-09-03


  • Make log's internal helper macros less likely to conflict with user-defined macros.

0.4.4 - 2018-08-17


  • Support 2018-style imports of the log macros.

0.4.3 - 2018-06-29


  • More code generation improvements.

0.4.2 - 2018-06-05


  • Log invocations now generate less code.


  • Example Logger implementations now properly set the max log level.

0.4.1 - 2017-12-30


  • Some doc links were fixed.

0.4.0 - 2017-12-24

The changes in this release include cleanup of some obscure functionality and a more robust public API designed to support bridges to other logging systems, and provide more flexibility to new features in the future.


Vast portions of the Rust ecosystem use the 0.3.x release series of log, and we don‘t want to force the community to go through the pain of upgrading every crate to 0.4.x at the exact same time. Along with 0.4.0, we’ve published a new 0.3.9 release which acts as a “shim” over 0.4.0. This will allow crates using either version to coexist without losing messages from one side or the other.

There is one caveat - a log message generated by a crate using 0.4.x but consumed by a logging implementation using 0.3.x will not have a file name or module path. Applications affected by this can upgrade their logging implementations to one using 0.4.x to avoid losing this information. The other direction does not lose any information, fortunately!

TL;DR Libraries should feel comfortable upgrading to 0.4.0 without treating that as a breaking change. Applications may need to update their logging implementation (e.g. env-logger) to a newer version using log 0.4.x to avoid losing module and file information.


  • The crate is now no_std by default.
  • Level and LevelFilter now implement Serialize and Deserialize when the serde feature is enabled.
  • The Record and Metadata types can now be constructed by third-party code via a builder API.
  • The logger free function returns a reference to the logger implementation. This, along with the ability to construct Records, makes it possible to bridge from another logging framework to this one without digging into the private internals of the crate. The standard error! warn!, etc, macros now exclusively use the public API of the crate rather than “secret” internal APIs.
  • Log::flush has been added to allow crates to tell the logging implementation to ensure that all “in flight” log events have been persisted. This can be used, for example, just before an application exits to ensure that asynchronous log sinks finish their work.


  • The shutdown and shutdown_raw functions have been removed. Supporting shutdown significantly complicated the implementation and imposed a performance cost on each logging operation.
  • The log_panics function and its associated nightly Cargo feature have been removed. Use the log-panics instead.


  • The Log prefix has been removed from type names. For example, LogLevelFilter is now LevelFilter, and LogRecord is now Record.
  • The MaxLogLevelFilter object has been removed in favor of a set_max_level free function.
  • The set_logger free functions have been restructured. The logger is now directly passed to the functions rather than a closure which returns the logger. set_logger now takes a &'static Log and is usable in no_std contexts in place of the old set_logger_raw. set_boxed_logger is a convenience function which takes a Box<Log> but otherwise acts like set_logger. It requires the std feature.
  • The file and module_path values in Record no longer have the 'static lifetime to support integration with other logging frameworks that don't provide a 'static lifetime for the equivalent values.
  • The file, line, and module_path values in Record are now Options to support integration with other logging frameworks that don't provide those values.

In the Future

  • We're looking to add support for structured logging - the inclusion of extra key-value pairs of information in a log event in addition to the normal string message. This should be able to be added in a backwards compatible manner to the 0.4.x series when the design is worked out.


Look at the release tags for information about older releases.