docs: consistent MSRV docs & policy explanation

README.md

@@ -253,6 +253,19 @@ attachment that `Future::instrument` does.
 [`Future::instrument`]: https://docs.rs/tracing-futures/latest/tracing_futures/trait.Instrument.html#method.instrument
 [instrument]: https://docs.rs/tracing/0.1.14/tracing/attr.instrument.html
 
+## Supported Rust Versions
+
+Tracing is built against the latest stable release. The minimum supported
+version is 1.40. The current Tracing version is not guaranteed to build on Rust
+versions earlier than the minimum supported version.
+
+Tracing follows the same compiler support policies as the rest of the Tokio
+project. The current stable Rust compiler and the three most recent minor
+versions before it will always be supported. For example, if the current stable
+compiler version is 1.45, the minimum supported version will not be increased
+past 1.42, three minor versions prior. Increasing the minimum supported compiler
+version is not considered a semver breaking change as long as doing so complies
+with this policy.
 
 ## Getting Help
 

tracing-appender/README.md

@@ -36,6 +36,10 @@ allows events and spans to be recorded in a non-blocking manner through a
 dedicated logging thread. It also provides a [`RollingFileAppender`][file_appender] 
 that can be used with _or_ without the non-blocking writer.
 
+*Compiler support: [requires `rustc` 1.40+][msrv]*
+
+[msrv]: #supported-rust-versions
+
 ## Usage
 
 Add the following to your `Cargo.toml`:
@@ -139,6 +143,20 @@ fn main() {
 [file_appender]: https://docs.rs/tracing-appender/latest/tracing_appender/rolling/struct.RollingFileAppender.html
 [fmt_subscriber]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/struct.Subscriber.html
 
+## Supported Rust Versions
+
+Tracing is built against the latest stable release. The minimum supported
+version is 1.40. The current Tracing version is not guaranteed to build on Rust
+versions earlier than the minimum supported version.
+
+Tracing follows the same compiler support policies as the rest of the Tokio
+project. The current stable Rust compiler and the three most recent minor
+versions before it will always be supported. For example, if the current stable
+compiler version is 1.45, the minimum supported version will not be increased
+past 1.42, three minor versions prior. Increasing the minimum supported compiler
+version is not considered a semver breaking change as long as doing so complies
+with this policy.
+
 ## License
 
 This project is licensed under the [MIT license](../LICENSE).

tracing-appender/src/lib.rs

@@ -7,6 +7,9 @@
 //! a dedicated logging thread. It also provides a [`RollingFileAppender`][file_appender] that can
 //! be used with _or_ without the non-blocking writer.
 //!
+//! *Compiler support: [requires `rustc` 1.40+][msrv]*
+//!
+//! [msrv]: #supported-rust-versions
 //! [file_appender]: ./rolling/struct.RollingFileAppender.html
 //! [tracing]: https://docs.rs/tracing/
 //!
@@ -104,6 +107,21 @@
 //!     .init();
 //! # }
 //! ```
+//!
+//! ## Supported Rust Versions
+//!
+//! Tracing is built against the latest stable release. The minimum supported
+//! version is 1.40. The current Tracing version is not guaranteed to build on
+//! Rust versions earlier than the minimum supported version.
+//!
+//! Tracing follows the same compiler support policies as the rest of the Tokio
+//! project. The current stable Rust compiler and the three most recent minor
+//! versions before it will always be supported. For example, if the current
+//! stable compiler version is 1.45, the minimum supported version will not be
+//! increased past 1.42, three minor versions prior. Increasing the minimum
+//! supported compiler version is not considered a semver breaking change as
+//! long as doing so complies with this policy.
+//!
 #![doc(html_root_url = "https://docs.rs/tracing-appender/0.1.1")]
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo.svg",

tracing-attributes/README.md

@@ -37,6 +37,10 @@ structured, event-based diagnostic information. This crate provides the
 
 Note that this macro is also re-exported by the main `tracing` crate.
 
+*Compiler support: [requires `rustc` 1.40+][msrv]*
+
+[msrv]: #supported-rust-versions
+
 ## Usage
 
 First, add this to your `Cargo.toml`:
@@ -46,7 +50,6 @@ First, add this to your `Cargo.toml`:
 tracing-attributes = "0.1.10"
 ```
 
-*Compiler support: requires rustc 1.39+*
 
 This crate provides the `#[instrument]` attribute for instrumenting a function
 with a `tracing` [span]. For example:
@@ -60,10 +63,23 @@ pub fn my_function(my_arg: usize) {
 }
 ```
 
-
 [`tracing`]: https://crates.io/crates/tracing
 [span]: https://docs.rs/tracing/latest/tracing/span/index.html
 
+## Supported Rust Versions
+
+Tracing is built against the latest stable release. The minimum supported
+version is 1.40. The current Tracing version is not guaranteed to build on Rust
+versions earlier than the minimum supported version.
+
+Tracing follows the same compiler support policies as the rest of the Tokio
+project. The current stable Rust compiler and the three most recent minor
+versions before it will always be supported. For example, if the current stable
+compiler version is 1.45, the minimum supported version will not be increased
+past 1.42, three minor versions prior. Increasing the minimum supported compiler
+version is not considered a semver breaking change as long as doing so complies
+with this policy.
+
 ## License
 
 This project is licensed under the [MIT license](LICENSE).

tracing-attributes/src/lib.rs

@@ -6,6 +6,10 @@
 //!
 //! Note that this macro is also re-exported by the main `tracing` crate.
 //!
+//! *Compiler support: [requires `rustc` 1.40+][msrv]*
+//!
+//! [msrv]: #supported-rust-versions
+//!
 //! ## Usage
 //!
 //! First, add this to your `Cargo.toml`:
@@ -15,8 +19,6 @@
 //! tracing-attributes = "0.1.10"
 //! ```
 //!
-//! *Compiler support: requires rustc 1.39+*
-//!
 //! The [`#[instrument]`][instrument] attribute can now be added to a function
 //! to automatically create and enter `tracing` [span] when that function is
 //! called. For example:
@@ -35,6 +37,21 @@
 //! [`tracing`]: https://crates.io/crates/tracing
 //! [span]: https://docs.rs/tracing/latest/tracing/span/index.html
 //! [instrument]: attr.instrument.html
+//!
+//! ## Supported Rust Versions
+//!
+//! Tracing is built against the latest stable release. The minimum supported
+//! version is 1.40. The current Tracing version is not guaranteed to build on
+//! Rust versions earlier than the minimum supported version.
+//!
+//! Tracing follows the same compiler support policies as the rest of the Tokio
+//! project. The current stable Rust compiler and the three most recent minor
+//! versions before it will always be supported. For example, if the current
+//! stable compiler version is 1.45, the minimum supported version will not be
+//! increased past 1.42, three minor versions prior. Increasing the minimum
+//! supported compiler version is not considered a semver breaking change as
+//! long as doing so complies with this policy.
+//!
 #![doc(html_root_url = "https://docs.rs/tracing-attributes/0.1.10")]
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo.svg",

tracing-core/README.md

@@ -53,8 +53,12 @@ The crate provides:
 In addition, it defines the global callsite registry and per-thread current
 dispatcher which other components of the tracing system rely on.
 
-## Usage
+*Compiler support: [requires `rustc` 1.40+][msrv]*
+
+[msrv]: #supported-rust-versions
 
+## Usage
+
 Application authors will typically not use this crate directly. Instead, they
 will use the [`tracing`] crate, which provides a much more fully-featured
 API. However, this crate's API will change very infrequently, so it may be used
@@ -71,15 +75,13 @@ The following crate feature flags are available:
 
 * `std`: Depend on the Rust standard library (enabled by default).
 
-   `no_std` users may disable this feature with `default-features = false`:
+  `no_std` users may disable this feature with `default-features = false`:
 
   ```toml
   [dependencies]
   tracing-core = { version = "0.1.14", default-features = false }
   ```
 
-  *Compiler support: requires rustc 1.39+*
-
   **Note**:`tracing-core`'s `no_std` support requires `liballoc`.
 
 [`tracing`]: ../tracing
@@ -94,6 +96,20 @@ The following crate feature flags are available:
 [`ValueSet`]: https://docs.rs/tracing-core/0.1.14/tracing_core/field/struct.ValueSet.html
 [`Dispatch`]: https://docs.rs/tracing-core/0.1.14/tracing_core/dispatcher/struct.Dispatch.html
 
+## Supported Rust Versions
+
+Tracing is built against the latest stable release. The minimum supported
+version is 1.40. The current Tracing version is not guaranteed to build on Rust
+versions earlier than the minimum supported version.
+
+Tracing follows the same compiler support policies as the rest of the Tokio
+project. The current stable Rust compiler and the three most recent minor
+versions before it will always be supported. For example, if the current stable
+compiler version is 1.45, the minimum supported version will not be increased
+past 1.42, three minor versions prior. Increasing the minimum supported compiler
+version is not considered a semver breaking change as long as doing so complies
+with this policy.
+
 ## License
 
 This project is licensed under the [MIT license](LICENSE).

tracing-core/src/lib.rs

@@ -23,6 +23,10 @@
 //! In addition, it defines the global callsite registry and per-thread current
 //! dispatcher which other components of the tracing system rely on.
 //!
+//! *Compiler support: [requires `rustc` 1.40+][msrv]*
+//!
+//! [msrv]: #supported-rust-versions
+//!
 //! ## Usage
 //!
 //! Application authors will typically not use this crate directly. Instead,
@@ -52,10 +56,23 @@
 //!   tracing-core = { version = "0.1.14", default-features = false }
 //!   ```
 //!
-//!   *Compiler support: requires rustc 1.39+*
-//!
 //!   **Note**:`tracing-core`'s `no_std` support requires `liballoc`.
 //!
+//! ## Supported Rust Versions
+//!
+//! Tracing is built against the latest stable release. The minimum supported
+//! version is 1.40. The current Tracing version is not guaranteed to build on
+//! Rust versions earlier than the minimum supported version.
+//!
+//! Tracing follows the same compiler support policies as the rest of the Tokio
+//! project. The current stable Rust compiler and the three most recent minor
+//! versions before it will always be supported. For example, if the current
+//! stable compiler version is 1.45, the minimum supported version will not be
+//! increased past 1.42, three minor versions prior. Increasing the minimum
+//! supported compiler version is not considered a semver breaking change as
+//! long as doing so complies with this policy.
+//!
+//!
 //! [`span::Id`]: span/struct.Id.html
 //! [`Event`]: event/struct.Event.html
 //! [`Subscriber`]: subscriber/trait.Subscriber.html

tracing-error/README.md

@@ -48,7 +48,9 @@ The crate provides the following:
 
 **Note**: This crate is currently experimental.
 
-*Compiler support: requires `rustc` 1.39+*
+*Compiler support: [requires `rustc` 1.40+][msrv]*
+
+[msrv]: #supported-rust-versions
 
 ## Usage
 
@@ -181,6 +183,20 @@ fn main() {
     - [`ExtractSpanTrace`] extension trait, for extracting `SpanTrace`s from
     behind `dyn Error` trait objects.
 
+## Supported Rust Versions
+
+Tracing is built against the latest stable release. The minimum supported
+version is 1.40. The current Tracing version is not guaranteed to build on Rust
+versions earlier than the minimum supported version.
+
+Tracing follows the same compiler support policies as the rest of the Tokio
+project. The current stable Rust compiler and the three most recent minor
+versions before it will always be supported. For example, if the current stable
+compiler version is 1.45, the minimum supported version will not be increased
+past 1.42, three minor versions prior. Increasing the minimum supported compiler
+version is not considered a semver breaking change as long as doing so complies
+with this policy.
+
 ## Related Crates
 
 In addition to this repository, here are also several third-party crates which

tracing-error/src/lib.rs

@@ -18,7 +18,9 @@
 //!
 //! **Note**: This crate is currently experimental.
 //!
-//! *Compiler support: requires `rustc` 1.39+*
+//! *Compiler support: [requires `rustc` 1.40+][msrv]*
+//!
+//! [msrv]: #supported-rust-versions
 //!
 //! ## Feature Flags
 //!
@@ -168,6 +170,21 @@
 //! [subscriber layer]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/layer/trait.Layer.html
 //! [`tracing`]: https://docs.rs/tracing
 //! [`std::error::Error`]: https://doc.rust-lang.org/stable/std/error/trait.Error.html
+//!
+//! ## Supported Rust Versions
+//!
+//! Tracing is built against the latest stable release. The minimum supported
+//! version is 1.40. The current Tracing version is not guaranteed to build on
+//! Rust versions earlier than the minimum supported version.
+//!
+//! Tracing follows the same compiler support policies as the rest of the Tokio
+//! project. The current stable Rust compiler and the three most recent minor
+//! versions before it will always be supported. For example, if the current
+//! stable compiler version is 1.45, the minimum supported version will not be
+//! increased past 1.42, three minor versions prior. Increasing the minimum
+//! supported compiler version is not considered a semver breaking change as
+//! long as doing so complies with this policy.
+//!
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![doc(html_root_url = "https://docs.rs/tracing-error/0.1.2")]
 #![doc(

tracing-flame/README.md

@@ -26,6 +26,9 @@ flamegraph/flamechart. Flamegraphs/flamecharts are useful for identifying perfor
 bottlenecks in an application. For more details, see Brendan Gregg's [post]
 on flamegraphs.
 
+*Compiler support: [requires `rustc` 1.40+][msrv]*
+
+[msrv]: #supported-rust-versions
 [post]: http://www.brendangregg.com/flamegraphs.html
 
 ## Usage
@@ -101,6 +104,20 @@ span is entered relative to others and get an accurate visual trace of
 the execution of your program. This representation is best created with a
 _flamechart_, which _does not_ sort or collapse identical stack frames.
 
+## Supported Rust Versions
+
+Tracing is built against the latest stable release. The minimum supported
+version is 1.40. The current Tracing version is not guaranteed to build on Rust
+versions earlier than the minimum supported version.
+
+Tracing follows the same compiler support policies as the rest of the Tokio
+project. The current stable Rust compiler and the three most recent minor
+versions before it will always be supported. For example, if the current stable
+compiler version is 1.45, the minimum supported version will not be increased
+past 1.42, three minor versions prior. Increasing the minimum supported compiler
+version is not considered a semver breaking change as long as doing so complies
+with this policy.
+
 ## License
 
 This project is licensed under the [MIT license](LICENSE).

tracing-flame/src/lib.rs

@@ -10,6 +10,9 @@
 //! issues bottlenecks in an application. For more details, see Brendan Gregg's [post]
 //! on flamegraphs.
 //!
+//! *Compiler support: [requires `rustc` 1.40+][msrv]*
+//!
+//! [msrv]: #supported-rust-versions
 //! [post]: http://www.brendangregg.com/flamegraphs.html
 //!
 //! ## Usage
@@ -91,6 +94,21 @@
 //! [`FlameLayer`]: struct.FlameLayer.html
 //! [`FlushGuard`]: struct.FlushGuard.html
 //! [`inferno-flamegraph`]: https://docs.rs/inferno/0.9.5/inferno/index.html#producing-a-flame-graph
+//!
+//! ## Supported Rust Versions
+//!
+//! Tracing is built against the latest stable release. The minimum supported
+//! version is 1.40. The current Tracing version is not guaranteed to build on
+//! Rust versions earlier than the minimum supported version.
+//!
+//! Tracing follows the same compiler support policies as the rest of the Tokio
+//! project. The current stable Rust compiler and the three most recent minor
+//! versions before it will always be supported. For example, if the current
+//! stable compiler version is 1.45, the minimum supported version will not be
+//! increased past 1.42, three minor versions prior. Increasing the minimum
+//! supported compiler version is not considered a semver breaking change as
+//! long as doing so complies with this policy.
+//!
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo.svg",
     issue_tracker_base_url = "https://github.com/tokio-rs/tracing/issues/"