Update Rust in CI to 1.72.0, clarify Wasmtime's MSRV (bytecodeallianc…

…e#6900)

* Update Rust in CI to 1.72.0

* Update CI, tooling, and docs for MSRV

This commit codifies an MSRV policy for Wasmtime at "stable minus two"
meaning that the latest three releases of Rust will be supported. This
is enforced on CI with a full test suite job running on Linux x86_64
with the minimum supported Rust version. The full test suite will use
the latest stable version. A downside of this approach is that new
changes may break MSRV support on non-Linux or non-x86_64 platforms and
we won't know about it, but that's deemed a minor enough risk at this
time.

A minor fix is applied to Wasmtime's `Cargo.toml` to support Rust 1.70.0
instead of requiring Rust 1.71.0

* Fix installation of rust

* Scrape MSRV from Cargo.toml

* Cranelift is the same as Wasmtime's MSRV now, more words too

* Fix a typo

.github/actions/install-rust/action.yml

@@ -5,7 +5,7 @@ inputs:
   toolchain:
     description: 'Default toolchan to install'
     required: false
-    default: '1.71.0'
+    default: 'default'
   lockfiles:
     description: 'Path glob for Cargo.lock files to use as cache keys'
     required: false
@@ -14,13 +14,28 @@ inputs:
 runs:
   using: composite
   steps:
+    - name: Install Rust
+      shell: bash
+      id: select
+      run: |
+        # Determine MSRV as N in `1.N.0` by looking at the `rust-version`
+        # located in the root `Cargo.toml`.
+        msrv=$(grep 'rust-version.*1' Cargo.toml | sed 's/.*\.\([0-9]*\)\..*/\1/')
+
+        if [ "${{ inputs.toolchain }}" = "default" ]; then
+          echo "version=1.$((msrv+2)).0" >> "$GITHUB_OUTPUT"
+        elif [ "${{ inputs.toolchain }}" = "msrv" ]; then
+          echo "version=1.$msrv.0" >> "$GITHUB_OUTPUT"
+        else
+          echo "version=${{ inputs.toolchain }}" >> "$GITHUB_OUTPUT"
+        fi
 
     - name: Install Rust
       shell: bash
       run: |
         rustup set profile minimal
-        rustup update "${{ inputs.toolchain }}" --no-self-update
-        rustup default "${{ inputs.toolchain }}"
+        rustup update "${{ steps.select.outputs.version }}" --no-self-update
+        rustup default "${{ steps.select.outputs.version }}"
 
         # Save disk space by avoiding incremental compilation. Also turn down
         # debuginfo from 2 to 0 to help save disk space.
@@ -31,11 +46,7 @@ runs:
         EOF
 
         # Deny warnings on CI to keep our code warning-free as it lands in-tree.
-        # Don't do this on nightly though, since there's a fair amount of
-        # warning churn there.
-        if [[ "${{ inputs.toolchain }}" != nightly* ]]; then
-          echo RUSTFLAGS="-D warnings" >> "$GITHUB_ENV"
-        fi
+        echo RUSTFLAGS="-D warnings" >> "$GITHUB_ENV"
 
         if [[ "${{ runner.os }}" = "macOS" ]]; then
           cat >> "$GITHUB_ENV" <<EOF

.github/workflows/main.yml

@@ -383,6 +383,8 @@ jobs:
       with:
         submodules: true
     - uses: ./.github/actions/install-rust
+      with:
+        toolchain: ${{ matrix.rust }}
 
     # Install targets in order to build various tests throughout the repo
     - run: rustup target add wasm32-wasi wasm32-unknown-unknown ${{ matrix.target }}

Cargo.toml

@@ -123,7 +123,9 @@ exclude = [
 version = "13.0.0"
 authors = ["The Wasmtime Project Developers"]
 edition = "2021"
-rust-version = "1.71.0"
+# Wasmtime's current policy is that this number can be no larger than the
+# current stable release of Rust minus 2.
+rust-version = "1.70.0"
 
 [workspace.dependencies]
 wasmtime-wmemcheck = { path = "crates/wmemcheck", version = "=13.0.0" }

ci/build-test-matrix.js

@@ -32,13 +32,22 @@ const names = fs.readFileSync(process.argv[3]).toString();
 //   on CI.
 // * `isa` - changes to `cranelift/codegen/src/$isa` will automatically run this
 //   test suite.
+// * `rust` - the Rust version to install, and if unset this'll be set to
+//   `default`
 const array = [
   {
     "os": "ubuntu-latest",
     "name": "Test Linux x86_64",
     "filter": "linux-x64",
     "isa": "x64"
   },
+  {
+    "os": "ubuntu-latest",
+    "name": "Test MSRV on Linux x86_64",
+    "filter": "linux-x64",
+    "isa": "x64",
+    "rust": "msrv",
+  },
   {
     "os": "macos-latest",
     "name": "Test macOS x86_64",
@@ -90,6 +99,12 @@ const array = [
   }
 ];
 
+for (let config of array) {
+  if (config.rust === undefined) {
+    config.rust = 'default';
+  }
+}
+
 function myFilter(item) {
   if (item.isa && names.includes(`cranelift/codegen/src/isa/${item.isa}`)) {
     return true;

crates/wasmtime/Cargo.toml

@@ -132,4 +132,4 @@ component-model = [
   "dep:encoding_rs",
 ]
 
-wmemcheck = ["wasmtime-runtime/wmemcheck", "wasmtime-cranelift/wmemcheck"]
+wmemcheck = ["wasmtime-runtime/wmemcheck", "wasmtime-cranelift?/wmemcheck"]

docs/contributing-coding-guidelines.md

@@ -21,13 +21,16 @@ your editor.
 
 ### Minimum Supported `rustc` Version
 
-Wasmtime supports the current stable version of Rust.
+Wasmtime and Cranelift support the latest three stable releases of Rust. This
+means that if the latest version of Rust is 1.72.0 then Wasmtime supports Rust
+1.70.0, 1.71.0, and 1.72.0. CI will test by default with 1.72.0 and there will
+be one job running the full test suite on Linux x86\_64 on 1.70.0.
 
-Cranelift supports stable Rust, and follows the [Rust Update Policy for
-Firefox].
+Some of the CI jobs depend on nightly Rust, for example to run rustdoc with
+nightly features, however these use pinned versions in CI that are updated
+periodically and the general repository does not depend on nightly features.
 
-Some of the developer scripts depend on nightly Rust, for example to run
-clippy and other tools, however we avoid depending on these for the main
-build.
+Updating Wasmtime's MSRV is done by editing the `rust-version` field in the
+workspace root's `Cargo.toml`
 
 [Rust Update Policy for Firefox]: https://wiki.mozilla.org/Rust_Update_Policy_for_Firefox#Schedule