Migrate to Rust 2021 Edition

- Change edition to 2021
- Increase MSRV to 1.56.0
- Remove `build.rs`, build-dependency on `autocfg`, and conditional
  compilation of methods requiring at least 1.56.0
- Update the CI matrix

.github/workflows/rust.yml

@@ -16,19 +16,14 @@ jobs:
         - macos-latest
         rust:
         - stable
-        - 1.52.0  # MSRV
+        - 1.56.0  # MSRV
         cargo_args:
         - ""
         - --features serde
         include:
-          # Also test on nightly and Rust versions between MSRV and stable
-          # where there is conditional compilation
           - os: ubuntu-latest
             rust: nightly
             cargo_args: ""
-          - os: ubuntu-latest
-            rust: 1.56.0
-            cargo_args: ""
 
     runs-on: ${{ matrix.os }}
 

CHANGELOG.md

@@ -10,17 +10,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * `#[must_use]` attribute to many methods, porting and extending several
   rust-lang/rust PRs
-* Method `shrink_to()` for Rust 1.56.0 and greater, ported from rust-lang/rust
-* Implementation of `From<[T; N]>` for `BinaryHeap<T>` for Rust 1.56.0 or
-  greater, ported from rust-lang/rust#84111
+* Method `shrink_to()`, ported from rust-lang/rust
+* Implementation of `From<[T; N]>` for `BinaryHeap<T>`, ported from
+  rust-lang/rust#84111
 * Links to referenced items in the documenation
 * Example of a min-heap, ported from rust-lang/rust#60451
 * Documentation of time complexities of several methods, ported from
   rust-lang/rust#60952
 
 ### Changed
 
-* Bump MSRV (minimum supported rust version) to rust 1.52.0.
+* Migrate to Rust 2021 Edition
+* Increase MSRV (minimum supported rust version) to rust 1.56.0.
 * Implement `From<BinaryHeap<T, C>>` for `Vec<T>` instead of `Into<Vec<T>>` for
   `BinaryHeap<T, C>`
 * Port rust-lang/rust#77435 improvement to rebuild heuristic of

Cargo.toml

@@ -8,10 +8,8 @@ repository = "https://github.com/sekineh/binary-heap-plus-rs"
 readme = "README.md"
 keywords = ["binary", "heap", "priority", "queue"]
 categories = ["data-structures", "algorithms", ]
-edition = "2018"
-
-[build-dependencies]
-autocfg = "1"
+edition = "2021"
+rust-version = "1.56.0"
 
 [dependencies]
 compare = "0.1.0"

README.md

@@ -26,9 +26,7 @@ This crate is based on the standard library's implementation of
 [`BinaryHeap`](https://doc.rust-lang.org/stable/std/collections/struct.BinaryHeap.html)
 from Rust 1.62.0.
 
-This crate requires Rust 1.52.0 or later.  A few of its APIs are only available
-for more recent versions of Rust where they have been stabilized in the
-standard library; see the documentation for specifics.
+The minimum supported Rust version is 1.56.0.
 
 # Changes
 

src/binary_heap.rs

@@ -21,8 +21,6 @@
 //!
 //! ```
 //! use std::cmp::Ordering;
-//! // Only required for Rust versions prior to 1.43.0.
-//! use std::usize;
 //! use binary_heap_plus::BinaryHeap;
 //!
 //! #[derive(Copy, Clone, Eq, PartialEq)]
@@ -1258,12 +1256,7 @@ impl<T, C> BinaryHeap<T, C> {
     /// heap.shrink_to(10);
     /// assert!(heap.capacity() >= 10);
     /// ```
-    ///
-    /// # Compatibility
-    ///
-    /// This feature requires Rust 1.56.0 or greater.
     #[inline]
-    #[cfg(rustc_1_56)]
     pub fn shrink_to(&mut self, min_capacity: usize) {
         self.data.shrink_to(min_capacity)
     }
@@ -1655,10 +1648,6 @@ impl<T: Ord> From<Vec<T>> for BinaryHeap<T> {
     }
 }
 
-/// # Compatibility
-///
-/// This trait is only implemented for Rust 1.56.0 or greater.
-#[cfg(rustc_1_56)]
 impl<T: Ord, const N: usize> From<[T; N]> for BinaryHeap<T> {
     /// ```
     /// use binary_heap_plus::BinaryHeap;