Raise the MSRVto 1.51.0

Nix's code hasn't changed.  However, Serde accidentally raised its MSRV
to 1.51.0 in a patch release, due to a Cargo bug.  They don't plan to
change it back.  Nix does not depend on Serde, but it's used by
cargo-hack, which we build as part of our CI process.  So we need to
either raise our MSRV, or else install a separate toolchain during CI
just to build cargo-hack.

serde-rs/serde#2255

.cirrus.yml

@@ -9,7 +9,7 @@ env:
   RUSTDOCFLAGS: -D warnings
   TOOL: cargo
   # The MSRV
-  TOOLCHAIN: 1.46.0
+  TOOLCHAIN: 1.51.0
   ZFLAGS:
 
 # Tests that don't require executing the build binaries
@@ -141,18 +141,18 @@ task:
   matrix:
     - name: Linux aarch64
       arm_container:
-        image: rust:1.46
+        image: rust:1.51
       env:
         RUSTFLAGS: --cfg graviton -D warnings
         TARGET: aarch64-unknown-linux-gnu
     - name: Linux x86_64
       container:
-        image: rust:1.46
+        image: rust:1.51
       env:
         TARGET: x86_64-unknown-linux-gnu
     - name: Linux x86_64 musl
       container:
-        image: rust:1.46
+        image: rust:1.51
       env:
         TARGET: x86_64-unknown-linux-musl
   setup_script:
@@ -178,7 +178,7 @@ task:
 # Tasks for cross-compiling, but no testing
 task:
   container:
-    image: rust:1.46
+    image: rust:1.51
   env:
     BUILD: check
   matrix:
@@ -208,27 +208,18 @@ task:
     - name: Illumos
       env:
         TARGET: x86_64-unknown-illumos
-        # illumos toolchain isn't available via rustup until 1.50
-        TOOLCHAIN: 1.50.0
-      container:
-        image: rust:1.50
     # Cross claims to support running tests on iOS, but it actually doesn't.
     # https://github.com/rust-embedded/cross/issues/535
     - name: iOS aarch64
       env:
         # cargo hack tries to invoke the iphonesimulator SDK for iOS
         NOHACK: 1
         TARGET: aarch64-apple-ios
-        # Rustup only supports cross-building from arbitrary hosts for iOS at
-        # 1.49.0 and above.  Below that it's possible to cross-build from a macOS
-        # host, but macOS VMs are more expensive than Linux VMs.
-        TOOLCHAIN: 1.49.0
     - name: iOS x86_64
       env:
         # cargo hack tries to invoke the iphonesimulator SDK for iOS
         NOHACK: 1
         TARGET: x86_64-apple-ios
-        TOOLCHAIN: 1.49.0
     # Cross testing on powerpc fails with "undefined reference to renameat2".
     # Perhaps cross is using too-old a version?
     - name: Linux powerpc
@@ -248,10 +239,6 @@ task:
     - name: macOS aarch64
       env:
         TARGET: aarch64-apple-darwin
-        # macOS aarch64 toolchain isn't available via rustup until 1.49
-        TOOLCHAIN: 1.49.0
-      container:
-        image: rust:1.49
     - name: NetBSD x86_64
       env:
         TARGET: x86_64-unknown-netbsd
@@ -265,7 +252,7 @@ task:
 
 task:
   container:
-    image: rust:1.46
+    image: rust:1.51
   env:
     BUILD: check
   name: Redox x86_64

CHANGELOG.md

@@ -43,6 +43,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ### Changed
 
+- The MSRV is now 1.51.0
+  ([#TODO](https://github.com/nix-rust/nix/pull/TODO))
 - Rewrote the aio module.  The new module:
   * Does more type checking at compile time rather than runtime.
   * Gives the caller control over whether and when to `Box` an aio operation.

README.md

@@ -89,7 +89,7 @@ Tier 3:
 
 ## Minimum Supported Rust Version (MSRV)
 
-nix is supported on Rust 1.46.0 and higher.  Its MSRV will not be
+nix is supported on Rust 1.51.0 and higher.  Its MSRV will not be
 changed in the future without bumping the major or minor version.
 
 ## Contributing