Lower MSRV to 1.56

Makes progress on #554

Author: joshlf

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
       matrix:
         # See `INTERNAL.md` for an explanation of these pinned toolchain
         # versions.
-        toolchain: [ "msrv", "stable", "nightly", "zerocopy-aarch64-simd", "zerocopy-generic-bounds-in-const-fn" ]
+        toolchain: [ "msrv", "stable", "nightly",  "zerocopy-generic-bounds-in-const-fn", "zerocopy-aarch64-simd", "zerocopy-panic-in-const", ]
         target: [
           "i686-unknown-linux-gnu",
           "x86_64-unknown-linux-gnu",
@@ -59,10 +59,13 @@ jobs:
             features: "--all-features"
           - toolchain: "stable"
             features: "--all-features"
+          - toolchain: "zerocopy-generic-bounds-in-const-fn"
+            features: "--all-features"
           - toolchain: "zerocopy-aarch64-simd"
             features: "--all-features"
-          - toolchain: "zerocopy-generic-bounds-in-const-fn"
+          - toolchain: "zerocopy-panic-in-const"
             features: "--all-features"
+
           # Exclude any combination for the zerocopy-derive crate which
           # uses zerocopy features.
           - crate: "zerocopy-derive"
@@ -75,10 +78,12 @@ jobs:
           # other than "msrv", "stable", and "nightly". These other versions
           # exist to exercise zerocopy behavior which differs by toolchain;
           # zerocopy-derive doesn't behave different on these toolchains.
+          - crate: "zerocopy-derive"
+            toolchain: "zerocopy-generic-bounds-in-const-fn"
           - crate: "zerocopy-derive"
             toolchain: "zerocopy-aarch64-simd"
           - crate: "zerocopy-derive"
-            toolchain: "zerocopy-generic-bounds-in-const-fn"
+            toolchain: "zerocopy-panic-in-const"
 
     name: Build & Test (crate:${{ matrix.crate }}, toolchain:${{ matrix.toolchain }}, target:${{ matrix.target }}, features:${{ matrix.features }})
 

Cargo.toml

@@ -20,7 +20,7 @@ authors = ["Joshua Liebow-Feeser <joshlf@google.com>"]
 description = "Utilities for zero-copy parsing and serialization"
 license = "BSD-2-Clause OR Apache-2.0 OR MIT"
 repository = "https://github.com/google/zerocopy"
-rust-version = "1.57.0"
+rust-version = "1.56.0"
 
 exclude = [".*"]
 
@@ -30,13 +30,16 @@ exclude = [".*"]
 # as high as the specified version. In the emitted `--cfg`, dashes are replaced
 # by underscores.
 
+# From 1.61.0, Rust supports generic types with trait bounds in `const fn`.
+zerocopy-generic-bounds-in-const-fn = "1.61.0"
+
 # When the "simd" feature is enabled, include SIMD types from the
 # `core::arch::aarch64` module, which was stabilized in 1.59.0. On earlier Rust
 # versions, these types require the "simd-nightly" feature.
 zerocopy-aarch64-simd = "1.59.0"
 
-# From 1.61.0, Rust supports generic types with trait bounds in `const fn`.
-zerocopy-generic-bounds-in-const-fn = "1.61.0"
+# Permit panicking in `const fn`s.
+zerocopy-panic-in-const = "1.57.0"
 
 [package.metadata.ci]
 # The versions of the stable and nightly compiler toolchains to use in CI.