Lower MSRV to 1.57

Makes progress on #554

.github/workflows/ci.yml

@@ -118,6 +118,17 @@ jobs:
           echo "Using non-nightly toolchain; not modifying RUSTFLAGS='$RUSTFLAGS' or MIRIFLAGS='$MIRIFLAGS'" | tee -a $GITHUB_STEP_SUMMARY
         fi
 
+    # On our MSRV, `cargo` does not know about the `rust-version` field. As a
+    # result, in `cargo.sh`, if we use our MSRV toolchain in order to run `cargo
+    # metadata`, we will not be able to extract the `rust-version` field. Thus,
+    # in `cargo.sh`, we explicitly do `cargo +stable metadata`. This requires a
+    # (more recent) stable toolchain to be installed. As of this writing, this
+    # toolchain is not used for anything else.
+    - name: Install stable Rust for use in 'cargo.sh'
+      uses: dtolnay/rust-toolchain@00b49be78f40fba4e87296b2ead62868750bdd83 # stable
+      with:
+        toolchain: stable
+
     - name: Install Rust with ${{ matrix.toolchain }} toolchain (${{ env.ZC_TOOLCHAIN }}) and target ${{ matrix.target }}
       uses: dtolnay/rust-toolchain@00b49be78f40fba4e87296b2ead62868750bdd83 # stable
       with:

Cargo.toml

@@ -20,7 +20,7 @@ authors = ["Joshua Liebow-Feeser <[email protected]>"]
 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 = "1.58.0"
+rust-version = "1.57.0"
 
 exclude = [".*"]
 

build.rs

@@ -7,6 +7,56 @@
 // This file may not be copied, modified, or distributed except according to
 // those terms.
 
+// Sometimes we want to use lints which were added after our MSRV.
+// `unknown_lints` is `warn` by default and we deny warnings in CI, so without
+// this attribute, any unknown lint would cause a CI failure when testing with
+// our MSRV.
+#![allow(unknown_lints)]
+#![deny(renamed_and_removed_lints)]
+#![deny(
+    anonymous_parameters,
+    deprecated_in_future,
+    late_bound_lifetime_arguments,
+    missing_copy_implementations,
+    missing_debug_implementations,
+    path_statements,
+    patterns_in_fns_without_body,
+    rust_2018_idioms,
+    trivial_numeric_casts,
+    unreachable_pub,
+    unsafe_op_in_unsafe_fn,
+    unused_extern_crates,
+    unused_qualifications,
+    variant_size_differences
+)]
+#![deny(
+    clippy::all,
+    clippy::alloc_instead_of_core,
+    clippy::arithmetic_side_effects,
+    clippy::as_underscore,
+    clippy::assertions_on_result_states,
+    clippy::as_conversions,
+    clippy::correctness,
+    clippy::dbg_macro,
+    clippy::decimal_literal_representation,
+    clippy::get_unwrap,
+    clippy::indexing_slicing,
+    clippy::missing_inline_in_public_items,
+    clippy::missing_safety_doc,
+    clippy::obfuscated_if_else,
+    clippy::perf,
+    clippy::print_stdout,
+    clippy::std_instead_of_core,
+    clippy::style,
+    clippy::suspicious,
+    clippy::todo,
+    clippy::undocumented_unsafe_blocks,
+    clippy::unimplemented,
+    clippy::unnested_or_patterns,
+    clippy::unwrap_used,
+    clippy::use_debug
+)]
+
 use std::{env, fs, process::Command, str};
 
 fn main() {
@@ -96,7 +146,7 @@ fn parse_version_cfgs_from_cargo_toml() -> Vec<VersionCfg> {
             // comment (which can happen if it's inside a string) since we authored
             // `Cargo.toml` and, in this section, we only put Rust version numbers
             // in strings.
-            let before_comment = line.split("#").next().expect(ITER_FIRST_NEXT_EXPECT_MSG);
+            let before_comment = line.split('#').next().expect(ITER_FIRST_NEXT_EXPECT_MSG);
             let before_comment_without_whitespace = before_comment.trim_start();
             if before_comment_without_whitespace.is_empty() {
                 return None;
@@ -121,7 +171,7 @@ fn parse_version_cfgs_from_cargo_toml() -> Vec<VersionCfg> {
             assert_eq!(equals_sign, "=", "{}", EXPECT_MSG);
 
             // Replace dashes with underscores.
-            let name = name.replace("-", "_");
+            let name = name.replace('-', "_");
 
             // Strip the quotation marks.
             let value = value.trim_start_matches('"').trim_end_matches('"');

cargo.sh

@@ -46,7 +46,15 @@ function pkg-meta {
   # causing the subsequent `cargo` invocation to rebuild unnecessarily. By
   # specifying a separate build directory here, we ensure that this never
   # clobbers the build artifacts used by the later `cargo` invocation.
-  CARGO_TARGET_DIR=target/cargo-sh cargo metadata --format-version 1 | jq -r ".packages[] | select(.name == \"zerocopy\").$1"
+  #
+  # In CI, make sure to use the default stable toolchain. If we're testing on
+  # our MSRV, then we also have our MSRV toolchain installed. As of this
+  # writing, our MSRV is low enough that the correspoding Rust toolchain's Cargo
+  # doesn't know about the `rust-version` field, and so if we were to use Cargo
+  # with that toolchain, `pkg-meta` would return `null` when asked to retrieve
+  # the `rust-version` field. This also requires `RUSTFLAGS=''` to override any
+  # unstable `RUSTFLAGS` set by the caller.
+  RUSTFLAGS='' CARGO_TARGET_DIR=target/cargo-sh cargo +stable metadata --format-version 1 | jq -r ".packages[] | select(.name == \"zerocopy\").$1"
 }
 
 function lookup-version {

src/lib.rs

@@ -5886,7 +5886,7 @@ mod tests {
 
                     assert_matches::assert_matches!(
                         actual, $expect,
-                        "layout({size_info:?}, {align}).validate_cast_and_convert_metadata({addr}, {bytes_len}, {cast_type:?})",
+                        "layout({:?}, {}).validate_cast_and_convert_metadata({}, {}, {:?})" ,size_info, align, addr, bytes_len, cast_type
                     );
                 });
             };
@@ -5981,7 +5981,8 @@ mod tests {
             {
                 let (size_info, align) = (layout.size_info, layout.align);
                 let debug_str = format!(
-                    "layout({size_info:?}, {align}).validate_cast_and_convert_metadata({addr}, {bytes_len}, {cast_type:?}) => ({elems}, {split_at})",
+                    "layout({:?}, {}).validate_cast_and_convert_metadata({}, {}, {:?}) => ({}, {})",
+                    size_info, align, addr, bytes_len, cast_type, elems, split_at
                 );
 
                 // If this is a sized type (no trailing slice), then `elems` is
@@ -6130,7 +6131,7 @@ mod tests {
 
                 // Avoid expensive allocation when running under Miri.
                 let assert_msg = if !cfg!(miri) {
-                    format!("\n{args:?}\nsize:{size}, align:{align}")
+                    format!("\n{:?}\nsize:{}, align:{}", args, size, align)
                 } else {
                     String::new()
                 };
@@ -6168,8 +6169,8 @@ mod tests {
                     // Avoid expensive allocation when running under Miri.
                     let assert_msg = if !cfg!(miri) {
                         format!(
-                            "{}\nvalidate_cast_and_convert_metadata({addr}, {size})",
-                            assert_msg
+                            "{}\nvalidate_cast_and_convert_metadata({}, {})",
+                            assert_msg, addr, size,
                         )
                     } else {
                         String::new()

src/macro_util.rs

@@ -363,7 +363,12 @@ pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
     // - The caller has guaranteed that alignment is not increased.
     // - We know that the returned lifetime will not outlive the input lifetime
     //   thanks to the lifetime bounds on this function.
-    unsafe { &*dst }
+    //
+    // TODO(#67): Once our MSRV is 1.58, replace this `transmute` with `&*dst`.
+    #[allow(clippy::transmute_ptr_to_ref)]
+    unsafe {
+        core::mem::transmute(dst)
+    }
 }
 
 /// Transmutes a mutable reference of one type to a mutable reference of another

src/util.rs

@@ -271,7 +271,7 @@ mod tests {
                 let align = NonZeroUsize::new(align).unwrap();
                 let want = alt_impl(n, align);
                 let got = round_down_to_next_multiple_of_alignment(n, align);
-                assert_eq!(got, want, "round_down_to_next_multiple_of_alignment({n}, {align})");
+                assert_eq!(got, want, "round_down_to_next_multiple_of_alignment({}, {})", n, align);
             }
         }
     }
@@ -295,7 +295,7 @@ mod proofs {
 
         let expected = model_impl(n, align);
         let actual = round_down_to_next_multiple_of_alignment(n, align);
-        assert_eq!(expected, actual, "round_down_to_next_multiple_of_alignment({n}, {align})");
+        assert_eq!(expected, actual, "round_down_to_next_multiple_of_alignment({}, {})", n, align);
     }
 
     // Restricted to nightly since we use the unstable `usize::next_multiple_of`
@@ -319,7 +319,7 @@ mod proofs {
 
         let expected = model_impl(len, align);
         let actual = padding_needed_for(len, align);
-        assert_eq!(expected, actual, "padding_needed_for({len}, {align})");
+        assert_eq!(expected, actual, "padding_needed_for({}, {})", len, align);
 
         let padded_len = actual + len;
         assert_eq!(padded_len % align, 0);

tests/trybuild.rs

@@ -17,7 +17,7 @@ fn ui() {
     let source_files_dirname = version.get_ui_source_files_dirname_and_maybe_print_warning();
 
     let t = trybuild::TestCases::new();
-    t.compile_fail(format!("tests/{source_files_dirname}/*.rs"));
+    t.compile_fail(format!("tests/{}/*.rs", source_files_dirname));
 }
 
 // The file `invalid-impls.rs` directly includes `src/macros.rs` in order to
@@ -37,5 +37,5 @@ fn ui_invalid_impls() {
     let source_files_dirname = version.get_ui_source_files_dirname_and_maybe_print_warning();
 
     let t = trybuild::TestCases::new();
-    t.compile_fail(format!("tests/{source_files_dirname}/invalid-impls/*.rs"));
+    t.compile_fail(format!("tests/{}/invalid-impls/*.rs", source_files_dirname));
 }

tests/ui-msrv/include_value_not_from_bytes.stderr

@@ -4,9 +4,9 @@ error[E0277]: the trait bound `NotZerocopy<u32>: FromBytes` is not satisfied
 13 | const NOT_FROM_BYTES: NotZerocopy<u32> = include_value!("../../testdata/include_value/data");
    |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `NotZerocopy<u32>`
    |
-note: required by a bound in `AssertIsFromBytes`
+note: required by `AssertIsFromBytes`
   --> tests/ui-msrv/include_value_not_from_bytes.rs:13:42
    |
 13 | const NOT_FROM_BYTES: NotZerocopy<u32> = include_value!("../../testdata/include_value/data");
-   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the macro `$crate::transmute` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui-msrv/transmute-dst-not-frombytes.stderr

@@ -4,9 +4,9 @@ error[E0277]: the trait bound `NotZerocopy: FromBytes` is not satisfied
 18 | const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
    |                                         ^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `NotZerocopy`
    |
-note: required by a bound in `AssertIsFromBytes`
+note: required by `AssertIsFromBytes`
   --> tests/ui-msrv/transmute-dst-not-frombytes.rs:18:41
    |
 18 | const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
-   |                                         ^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   |                                         ^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui-msrv/transmute-mut-dst-not-frombytes.stderr

@@ -4,9 +4,9 @@ error[E0277]: the trait bound `Dst: FromBytes` is not satisfied
 24 | const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `Dst`
    |
-note: required by a bound in `AssertDstIsFromBytes`
+note: required by `AssertDstIsFromBytes`
   --> tests/ui-msrv/transmute-mut-dst-not-frombytes.rs:24:38
    |
 24 | const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
-   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui-msrv/transmute-mut-dst-not-intobytes.stderr

@@ -4,9 +4,9 @@ error[E0277]: the trait bound `Dst: AsBytes` is not satisfied
 24 | const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `Dst`
    |
-note: required by a bound in `AssertDstIsIntoBytes`
+note: required by `AssertDstIsIntoBytes`
   --> tests/ui-msrv/transmute-mut-dst-not-intobytes.rs:24:36
    |
 24 | const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
-   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsIntoBytes`
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui-msrv/transmute-mut-dst-not-nocell.stderr

@@ -4,9 +4,9 @@ error[E0277]: the trait bound `Dst: NoCell` is not satisfied
 24 | const DST_NOT_NO_CELL: &mut Dst = transmute_mut!(&mut Src);
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `NoCell` is not implemented for `Dst`
    |
-note: required by a bound in `AssertDstIsNoCell`
+note: required by `AssertDstIsNoCell`
   --> tests/ui-msrv/transmute-mut-dst-not-nocell.rs:24:35
    |
 24 | const DST_NOT_NO_CELL: &mut Dst = transmute_mut!(&mut Src);
-   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsNoCell`
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui-msrv/transmute-mut-dst-unsized.stderr

@@ -5,11 +5,11 @@ error[E0277]: the size for values of type `[u8]` cannot be known at compilation
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[u8]`
-note: required by a bound in `AssertDstIsSized`
+note: required by `AssertDstIsSized`
   --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
    |
 17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsSized`
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
@@ -58,11 +58,11 @@ error[E0277]: the size for values of type `[u8]` cannot be known at compilation
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[u8]`
-note: required by a bound in `MaxAlignsOf::<T, U>::new`
+note: required by `MaxAlignsOf::<T, U>::new`
   --> src/macro_util.rs
    |
-   | impl<T, U> MaxAlignsOf<T, U> {
-   |         ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the size for values of type `[u8]` cannot be known at compilation time