cpubits: test detection results in CI (#1418)

Adds tests for the detection results that confirm the result matches
`target_pointer_width` on every platform except `wasm`.

Updates the CI config to test on
- 32-bit Linux
- 64-bit Linux
- 64-bit Windows
- 64-bit macOS
- `wasm32-wasip1` target on `wasmtime`

Author: tarcieri

.github/workflows/cpubits.yml

@@ -17,17 +17,56 @@ env:
   RUSTFLAGS: "-Dwarnings"
 
 jobs:
-  build:
+  test:
+    strategy:
+      matrix:
+        include:
+          # 32-bit Linux
+          - target: i686-unknown-linux-gnu
+            platform: ubuntu-latest
+            rust: 1.85.0 # MSRV
+            deps: sudo apt update && sudo apt install gcc-multilib
+
+          # 64-bit Linux
+          - target: x86_64-unknown-linux-gnu
+            platform: ubuntu-latest
+            rust: 1.85.0 # MSRV
+
+          # 64-bit Windows
+          - target: x86_64-pc-windows-msvc
+            platform: windows-latest
+            rust: 1.85.0 # MSRV
+
+          # 64-bit macOS
+          - target: x86_64-apple-darwin
+            platform: macos-latest
+            rust: 1.85.0 # MSRV
+    runs-on: ${{ matrix.platform }}
+    steps:
+      - uses: actions/checkout@v6
+      - uses: RustCrypto/actions/cargo-cache@master
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+          targets: ${{ matrix.target }}
+      - run: ${{ matrix.deps }}
+      - run: cargo test --target ${{ matrix.target }}
+
+  # Test WASM using `wasm32-wasip1` target on `wasmtime`
+  test-wasm:
     strategy:
       matrix:
         rust:
           - 1.85 # MSRV
           - stable
     runs-on: ubuntu-latest
+    env:
+      CARGO_TARGET_WASM32_WASIP1_RUNNER: "wasmtime"
     steps:
       - uses: actions/checkout@v6
-      - uses: RustCrypto/actions/cargo-cache@master
+      - uses: bytecodealliance/actions/wasmtime/setup@v1
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}
-      - run: cargo test
+          targets: wasm32-wasip1
+      - run: cargo test --target wasm32-wasip1

cpubits/src/lib.rs

@@ -175,7 +175,7 @@ macro_rules! cpubits {
         $crate::cpubits! {
             #[cfg(enable_64bit(
                 // `cfg` selector for 64-bit targets (implicitly `any`)
-                target_family = "wasm",
+                target_arch = "wasm32"
             ))]
             16 => { $( $tokens32 )* }
             32 => { $( $tokens32 )* }
@@ -268,46 +268,64 @@ macro_rules! cfg_if {
 
 #[cfg(test)]
 mod tests {
-    mod two_arms {
+    /// Return an integer that maps to the number of bits `cpubits` detected.
+    fn detected_bits() -> u32 {
         cpubits! {
-            16 | 32 => {
-                pub type Word = u32;
-            }
-            64 => {
-                pub type Word = u64;
-            }
+            16 => { 16 }
+            32 => { 32 }
+            64 => { 64 }
         }
+    }
 
-        #[test]
-        fn word_matches_pointer_size() {
-            match size_of::<usize>() {
-                2 | 4 => {
-                    assert_eq!(size_of::<Word>(), 4);
-                }
-                8 => {
-                    assert_eq!(size_of::<Word>(), 8);
-                }
-                _ => todo!("unsupported target pointer width"),
-            }
+    /// Return an integer that maps to `target_pointer_width`.
+    #[allow(dead_code)]
+    fn detect_pointer_width() -> u32 {
+        if cfg!(target_pointer_width = "16") {
+            16
+        } else if cfg!(target_pointer_width = "32") {
+            32
+        } else if cfg!(target_pointer_width = "64") {
+            64
+        } else {
+            unreachable!("rustc only support 16, 32, and 64-bit pointer widths")
         }
     }
 
-    mod three_arms {
-        cpubits! {
-            16 => {
-                pub type Word = u16;
-            }
-            32 => {
-                pub type Word = u32;
-            }
-            64 => {
-                pub type Word = u64;
+    /// Return the expected number of bits for the target.
+    fn expected_bits() -> u32 {
+        // Duplicated 64-bit override predicates need to go here
+        if cfg!(target_arch = "wasm32") {
+            64
+        } else {
+            detect_pointer_width()
+        }
+    }
+
+    #[test]
+    fn cpubits_works() {
+        assert_eq!(detected_bits(), expected_bits());
+    }
+
+    /// Explicit test for WASM so we can see the predicate is working
+    #[cfg(target_arch = "wasm32")]
+    #[test]
+    fn cpubits_on_wasm_is_64bit() {
+        assert_eq!(detected_bits(), 64);
+    }
+
+    #[test]
+    fn cpubits_16_or_32_vs_64() {
+        fn bits32or64() -> u32 {
+            cpubits! {
+                16 | 32 => { 32 }
+                64 => { 64 }
             }
         }
 
-        #[test]
-        fn word_matches_pointer_size() {
-            assert_eq!(size_of::<Word>(), size_of::<usize>());
+        match expected_bits() {
+            16 | 32 => assert_eq!(32, bits32or64()),
+            64 => assert_eq!(64, bits32or64()),
+            bits => unreachable!("#{bits}-bits should be one of: 16, 32, 64"),
         }
     }
 }