Fix private field breaking `#` operator in macros

Fixes issue #364

Release Notes

Fixed

• Fix use of # operator in macros due to private field (issue #364)
  • Thanks to @Manishearth for identifying this.
• ci: Check the tests pass with -Zminimal-versions

Move back to erased_serde v0.3

The upgrade from erased_serde v0.3 to v0.4 in v2.8.0 was a breaking change, as it affected the public API. In the future, we may find a way to upgrade in a backwards-compatible manner. This should not affect normal users of the API but could break drains supporting nested-values.

I (@Techcable) apologize for this breakage and have yanked the 2.8.0 release due to this issue. I will try to setup cargo-semver-checks in the CI to avoid this in the future.

Fixed

• Restore compatibility with erased-serde version 0.3.
  • Compatibility with erased-serde version 0.4 may be provided again in a
    future version, but will be done so in a backwards compatible way.
  • Thanks to @demurgos for recognizing and fixing this in PR #359
• Ensure compatibility with -Zminimal-versions flag by specifying minimal dependency versions (fixes #357)

Enable nested-values feature by default

This is the biggest slog release since v2.0! It contains many smaller fixes and improvements to slog that have been accumulated across 5 years and 127 commits.

The nested-values feature was already present in slog, and allows logging serde::Serialize types in addition to primitives. Previously, the nested-values feature had to be enabled not just in slog but also in each drain crate (slog_json, slog_term, slog_async, etc). Enabling this feature by default makes the crate easier to use and avoids several papercts. It should have no runtime overhead if not used and low compile-time overhead thanks to the new serde_core crate.

Another major feature is Logger::flush, which explicitly flushes buffered log messages. The next major release of slog_json, slog_async, etc., will also include support for this feature, in addition to enabling nested-values by default.

Changelog

The following has been copied from CHANGELOG.md

Highlights

• Enables the nested-values feature by default.
  The next major release of slog_json, slog_term, etc should also enable this feature by default.
• Added Logger::flush and Drain::flush methods.
• Improved support for logging errors
  • Have # log specifier transparently support & references to error
  • Implement slog::Value for Box<dyn std::error::Error> and anyhow::Error
• Define a prelude module for common imports
• Upgraded to Rust 2018 and require Rust 1.61
  • Deprecate the old slog_log! macros in favor of slog::log!
• Many internal improvements & bug fixes

Changed

• Enables the nested-values feature by default.
• Updated to Rust 2018
  • NOTE: Old 2015 crates will still work because of excellent 2015/2018 compatibility
• Bump MSRV to 1.61
  • This is already required for erased-serde, syn, serde_core, and many other important crates in the rust ecosystem.
• Update erased-serde from v0.3 to v0.4
• Depend on serde_core rather than serde to reduce compile times.

Added

• Added a Logger::flush and Drain::flush methods
  • Since this is a new method, not all drains implement it.
    Calling it on an unsupported drain will give an error
• Define a prelude module for common imports.
  Replace use slog::{Serde, Logger, info, debug, trace} with use slog::prelude::*
• Optionally implement Drain for parking_lot::Mutex.
  This is noticeably faster than std::sync::Mutex, is smaller, and avoids poisoning.
  • This feature has a separate name per version to allow supporting multiple versions of parking_lot at once. The current version (v0.12) has feature name parking_lot_0_12
• Implement slog::Value for dyn std::error::Error and Box<dyn std::error:Error (along with the Send/Sync versions).
• Optionally implement slog::Value for anyhow::Error (requires anyhow feature)
• Add ErrorRef wrapper to enable logging error references (PR #327)
  • The # error formatter in macros was updated to automatically select ErrorValue or ErrorRef (PR #328)
• Add emit_bytes method (PR #290)
  • Control formatting using BytesKind enum
• Implement Value for std::borrow::Cow

Deprecated

• Deprecate old prefixed macros like slog_log.
  Rust 2018 macro paths like slog::log! make these unnecessary.

Fixed

• Fix logging of references to errors (resolved by introduction of ErrorRef in PR #327)
• Take advantage of the fact that in 1.81 std::error::Error has been moved to core.
  On this rust version, slog now supports the error trait without requiring std.
• Add #[must_use] to most public types, including slog::Logger, slog::OwnedKV, and slog::FnValue.
• Give a descriptive error when the nested-values feature is unsupported.
• Alias the slog::Never type to std::convert::Infallible, fixing issue #209.
• doc: Fix typo in slog::Value docs (issue #335)
  • Thank you to @larswirzenius for noticing this!
• doc: Fix "lazy continuation" in slog::Logger doc
  • This mistake was caught by a new lint #[warn(clippy::doc_lazy_continuation)]
• Fix some internal warnings
  • Example: Avoid the new #[warn(unexpected_cfgs)] lint.
  • The crate almost passes clippy::pedantic now, except for a few very verbose lints like clippy::must-use-candidate
  • None of these changes should affect user crates
• Stop requiring the serde_derive crate to implement the nested-values feature.
  We depend on the new serde_core instead of even requiring serde.
• The nested-values feature no longer requires serde/std (was a mistake).
• Always support 128-bit integers, even on the wasm32-unknown-emscripten target.
• Fix support for feature="nothreads"
  • Internal refactoring to make different feature combos much easier (PR #301)
• Switch from Travis CI to Github Actions (fixes #294)
  • rustfmt --check now run by default
  • Require clippy to succeed without warnings
  • Require all feature combinations to pass tests.
    • Make exception for nested-values feature on MSRV (1.49),
      because erased-serde dependency requires edition="2021" (needs 1.56)
• Fix # format when not used as a last argument.
• Fix duplicate AsRef<str> implementations when using dynamic-keys feature.
• Fix incorrect 'long' name for slog::Level::Warning (fixes issue #282)