metrics-macros

Maintenance release.

Added

• When describing a metric, a constant can now be used for the description itself.
• Label keys can now be general expressions i.e. constants or variables. Due to limitations in how procedural macros work, and the facilities available in stable Rust for const traits, even &'static str constants will cause allocations when used for emitting a metric.

Changed

• Correctly scoped the required features of various dependencies to reduce build times/transitive dependencies.
• Updated macros to coincide with the update to metrics for metric handles. This includes renaming register_* macros to describe_*, which are purely for providing data that describes a metric but does not initialize it in any way, and providing new register_* macros which do initialize a metric.
• Updated the describe_* macros -- née register_* -- to require a description, and an optional unit. As describing a metric does not register it in the sense of ensuring that it is present on the output of an exporter, having the description be optional no longer makes sense.
• Additionally, the describe macros no longer take labels. In practice, varying the description of a specific metric based on label values would be counter-intuitive, and to support this corner case requires adds significant complexity to the macro parsing logic.

Removed

• Two unecessary dependencies, lazy_static and regex.

Changed

• Removed unnecessary proc-macro-hack dependency.

Changed

• Updates to macros to support the removal of NameParts and related machinery.

Changed

• Updates to macros to support changes in Recorder around how keys are taken.

Changed

• Added support for owned strings as metric names. #170

Added

• Effective birth of the crate.