chore: update MSRVs from 1.42 to 1.49 (#1913)

This updates all crates' MSRVs to 1.49 if they were not already greater
than that (`tracing-appender` is at 1.53). Rust 1.49+ is required to
update `parking_lot` to v0.12 (see #1878). Also, `futures-task` (which I
believe is only needed as a transitive dep) now needs 1.45+, so this
also fixes our CI build.

Because `tracing-opentelemetry` previously required 1.46.0, it had a
separate CI MSRV job. Since 1.49.0 is greater than 1.46.0, the separate
check for `tracing-opentelemetry` is no longer needed.

In the process, I removed deprecated uses of
`core::atomic::spin_loop_hint`, which is replaced with
`core::hint::spin_loop` in 1.49.

.github/workflows/CI.yml

@@ -28,56 +28,6 @@ env:
   RUST_BACKTRACE: short
 
 jobs:
-  check-msrv:
-    # Run `cargo check` on our minimum supported Rust version (1.42.0).
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@main
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: 1.42.0
-        profile: minimal
-        override: true
-    - name: Check
-      uses: actions-rs/cargo@v1
-      with:
-        command: check
-        args: --all --exclude=tracing-appender --exclude=tracing-opentelemetry
-
-  # TODO: remove this once tracing's MSRV is bumped.
-  check-msrv-appender:
-    # Run `cargo check` on our minimum supported Rust version (1.53.0).
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@main
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: 1.53.0
-        profile: minimal
-        override: true
-    - name: Check
-      uses: actions-rs/cargo@v1
-      with:
-        command: check
-        args: --lib=tracing-appender
-
-  # TODO: remove this once tracing's MSRV is bumped.
-  check-msrv-opentelemetry:
-    # Run `cargo check` on our minimum supported Rust version (1.46.0).
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@main
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: 1.46.0
-        profile: minimal
-        override: true
-    - name: Check
-      uses: actions-rs/cargo@v1
-      with:
-        command: check
-        args: --package=tracing-opentelemetry
-
   check:
     # Run `cargo check` first to ensure that the pushed code at least compiles.
     runs-on: ubuntu-latest

.github/workflows/check_msrv.yml

@@ -0,0 +1,63 @@
+name: Check MSRV
+
+on:
+  push:
+    branches:
+    - master
+    - "v0.1.x"
+  pull_request: {}
+
+env:
+  # Disable incremental compilation.
+  #
+  # Incremental compilation is useful as part of an edit-build-test-edit cycle,
+  # as it lets the compiler avoid recompiling code that hasn't changed. However,
+  # on CI, we're not making small edits; we're almost always building the entire
+  # project from scratch. Thus, incremental compilation on CI actually
+  # introduces *additional* overhead to support making future builds
+  # faster...but no future builds will ever occur in any given CI environment.
+  #
+  # See https://matklad.github.io/2021/09/04/fast-rust-builds.html#ci-workflow
+  # for details.
+  CARGO_INCREMENTAL: 0
+  # Allow more retries for network requests in cargo (downloading crates) and
+  # rustup (installing toolchains). This should help to reduce flaky CI failures
+  # from transient network timeouts or other issues.
+  CARGO_NET_RETRY: 10
+  RUSTUP_MAX_RETRIES: 10
+  # Don't emit giant backtraces in the CI logs.
+  RUST_BACKTRACE: short
+
+jobs:
+  check-msrv:
+    # Run `cargo check` on our minimum supported Rust version (1.49.0).
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@main
+    - uses: actions-rs/toolchain@v1
+      with:
+        toolchain: 1.49.0
+        profile: minimal
+        override: true
+    - name: Check
+      uses: actions-rs/cargo@v1
+      with:
+        command: check
+        args: --all --exclude=tracing-appender
+
+  # TODO: remove this once tracing's MSRV is bumped.
+  check-msrv-appender:
+    # Run `cargo check` on our minimum supported Rust version (1.53.0).
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@main
+    - uses: actions-rs/toolchain@v1
+      with:
+        toolchain: 1.53.0
+        profile: minimal
+        override: true
+    - name: Check
+      uses: actions-rs/cargo@v1
+      with:
+        command: check
+        args: --lib=tracing-appender

README.md

@@ -252,7 +252,7 @@ attachment that `Future::instrument` does.
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.42. The current Tracing version is not guaranteed to build on Rust
+version is 1.49. 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

examples/Cargo.toml

@@ -3,7 +3,7 @@ name = "tracing-examples"
 version = "0.0.0"
 publish = false
 edition = "2018"
-rust-version = "1.42.0"
+rust-version = "1.49.0"
 
 [features]
 default = []

tracing-attributes/Cargo.toml

@@ -28,7 +28,7 @@ keywords = ["logging", "tracing", "macro", "instrument", "log"]
 license = "MIT"
 readme = "README.md"
 edition = "2018"
-rust-version = "1.42.0"
+rust-version = "1.49.0"
 
 [lib]
 proc-macro = true

tracing-attributes/README.md

@@ -37,7 +37,7 @@ 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` 1.42+][msrv]*
+*Compiler support: [requires `rustc` 1.49+][msrv]*
 
 [msrv]: #supported-rust-versions
 
@@ -69,7 +69,7 @@ pub fn my_function(my_arg: usize) {
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.42. The current Tracing version is not guaranteed to build on Rust
+version is 1.49. 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

tracing-attributes/src/lib.rs

@@ -6,7 +6,7 @@
 //!
 //! Note that this macro is also re-exported by the main `tracing` crate.
 //!
-//! *Compiler support: [requires `rustc` 1.42+][msrv]*
+//! *Compiler support: [requires `rustc` 1.49+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //!
@@ -41,7 +41,7 @@
 //! ## Supported Rust Versions
 //!
 //! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.42. The current Tracing version is not guaranteed to build on
+//! version is 1.49. 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

tracing-core/Cargo.toml

@@ -24,7 +24,7 @@ categories = [
 ]
 keywords = ["logging", "tracing", "profiling"]
 edition = "2018"
-rust-version = "1.42.0"
+rust-version = "1.49.0"
 
 [features]
 default = ["std", "valuable/std"]

tracing-core/README.md

@@ -53,7 +53,7 @@ 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.
 
-*Compiler support: [requires `rustc` 1.42+][msrv]*
+*Compiler support: [requires `rustc` 1.49+][msrv]*
 
 [msrv]: #supported-rust-versions
 
@@ -99,7 +99,7 @@ The following crate feature flags are available:
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.42. The current Tracing version is not guaranteed to build on Rust
+version is 1.49. 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

tracing-core/src/lib.rs

@@ -23,7 +23,7 @@
 //! 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` 1.42+][msrv]*
+//! *Compiler support: [requires `rustc` 1.49+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //!
@@ -92,7 +92,7 @@
 //! ## Supported Rust Versions
 //!
 //! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.42. The current Tracing version is not guaranteed to build on
+//! version is 1.49. 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

tracing-core/src/spin/once.rs

@@ -1,9 +1,7 @@
 use core::cell::UnsafeCell;
 use core::fmt;
+use core::hint::spin_loop;
 use core::sync::atomic::{AtomicUsize, Ordering};
-// TODO(eliza): replace with `core::hint::spin_loop` once our MSRV supports it.
-#[allow(deprecated)]
-use core::sync::atomic::spin_loop_hint as cpu_relax;
 
 /// A synchronization primitive which can be used to run a one-time global
 /// initialization. Unlike its std equivalent, this is generalized so that the
@@ -109,10 +107,8 @@ impl<T> Once<T> {
             match status {
                 INCOMPLETE => unreachable!(),
                 RUNNING => {
-                    // TODO(eliza): replace with `core::hint::spin_loop` once our MSRV supports it.
-                    #[allow(deprecated)]
                     // We spin
-                    cpu_relax();
+                    spin_loop();
                     status = self.state.load(Ordering::SeqCst)
                 }
                 PANICKED => panic!("Once has panicked"),
@@ -138,9 +134,7 @@ impl<T> Once<T> {
                 INCOMPLETE => return None,
 
                 RUNNING => {
-                    // TODO(eliza): replace with `core::hint::spin_loop` once our MSRV supports it.
-                    #[allow(deprecated)]
-                    cpu_relax() // We spin
+                    spin_loop() // We spin
                 }
                 COMPLETE => return Some(self.force_get()),
                 PANICKED => panic!("Once has panicked"),

tracing-error/Cargo.toml

@@ -32,7 +32,7 @@ keywords = [
     "backtrace"
 ]
 edition = "2018"
-rust-version = "1.42.0"
+rust-version = "1.49.0"
 
 [features]
 default = ["traced-error"]

tracing-error/README.md

@@ -48,7 +48,7 @@ The crate provides the following:
 
 **Note**: This crate is currently experimental.
 
-*Compiler support: [requires `rustc` 1.42+][msrv]*
+*Compiler support: [requires `rustc` 1.49+][msrv]*
 
 [msrv]: #supported-rust-versions
 
@@ -186,7 +186,7 @@ fn main() {
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.42. The current Tracing version is not guaranteed to build on Rust
+version is 1.49. 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

tracing-error/src/lib.rs

@@ -18,7 +18,7 @@
 //!
 //! **Note**: This crate is currently experimental.
 //!
-//! *Compiler support: [requires `rustc` 1.42+][msrv]*
+//! *Compiler support: [requires `rustc` 1.49+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //!
@@ -174,7 +174,7 @@
 //! ## Supported Rust Versions
 //!
 //! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.42. The current Tracing version is not guaranteed to build on
+//! version is 1.49. 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

tracing-flame/Cargo.toml

@@ -19,7 +19,7 @@ categories = [
     "asynchronous",
 ]
 keywords = ["tracing", "subscriber", "flamegraph", "profiling"]
-rust-version = "1.42.0"
+rust-version = "1.49.0"
 
 [features]
 default = ["smallvec"]

tracing-flame/README.md

@@ -26,7 +26,7 @@ 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` 1.42+][msrv]*
+*Compiler support: [requires `rustc` 1.49+][msrv]*
 
 [msrv]: #supported-rust-versions
 [post]: http://www.brendangregg.com/flamegraphs.html
@@ -106,7 +106,7 @@ _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 1.42. The current Tracing version is not guaranteed to build on Rust
+version is 1.49. 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

tracing-flame/src/lib.rs

@@ -10,7 +10,7 @@
 //! issues bottlenecks in an application. For more details, see Brendan Gregg's [post]
 //! on flamegraphs.
 //!
-//! *Compiler support: [requires `rustc` 1.42+][msrv]*
+//! *Compiler support: [requires `rustc` 1.49+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //! [post]: http://www.brendangregg.com/flamegraphs.html
@@ -98,7 +98,7 @@
 //! ## Supported Rust Versions
 //!
 //! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.42. The current Tracing version is not guaranteed to build on
+//! version is 1.49. 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

tracing-futures/Cargo.toml

@@ -16,7 +16,7 @@ categories = [
 ]
 keywords = ["logging", "profiling", "tracing", "futures", "async"]
 license = "MIT"
-rust-version = "1.42.0"
+rust-version = "1.49.0"
 
 [features]
 default = ["std-future", "std"]

tracing-futures/README.md

@@ -51,14 +51,14 @@ The crate provides the following traits:
 [`Subscriber`]: https://docs.rs/tracing/latest/tracing/subscriber/index.html
 [`tracing`]: https://crates.io/crates/tracing
 
-*Compiler support: [requires `rustc` 1.42+][msrv]*
+*Compiler support: [requires `rustc` 1.49+][msrv]*
 
 [msrv]: #supported-rust-versions
 
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.42. The current Tracing version is not guaranteed to build on Rust
+version is 1.49. 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

tracing-futures/src/lib.rs

@@ -15,7 +15,7 @@
 //! * [`WithSubscriber`] allows a `tracing` [`Subscriber`] to be attached to a
 //!   future, sink, stream, or executor.
 //!
-//! *Compiler support: [requires `rustc` 1.42+][msrv]*
+//! *Compiler support: [requires `rustc` 1.49+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //!
@@ -62,7 +62,7 @@
 //! ## Supported Rust Versions
 //!
 //! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.42. The current Tracing version is not guaranteed to build on
+//! version is 1.49. 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