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

.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 supports 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