Add CI check for odd BufEncoder CAP

Add a test file that has an odd capacity BufEncoder.

Add a CI check that the test file does not compile.

.github/workflows/README.md

@@ -24,3 +24,4 @@ Run from rust.yml unless stated otherwise. Unfortunately we are now exceeding th
 10. `Arch32bit`
 11. `Cross`
 12. `Format`
+13. `Compile tests`

.github/workflows/rust.yaml

@@ -218,3 +218,14 @@ jobs:
         run: rustup component add rustfmt
       - name: "Check formatting"
         run: cargo +nightly fmt --all -- --check
+
+  Compile:
+    name: Compile tests
+    runs-on: ubuntu-latest
+    steps:
+      - name: "Checkout repo"
+        uses: actions/checkout@v4
+      - name: "Select toolchain"
+        uses: dtolnay/rust-toolchain@stable
+      - name: "Run compile tests"
+        run: ./contrib/compile-tests.sh

Cargo.toml

@@ -18,7 +18,7 @@ all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
 [workspace]
-members = ["fuzz"]
+members = ["fuzz", "tests/compiletest"]
 
 [features]
 default = ["std"]

contrib/compile-tests.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+# Check that an odd BufEncoder capacity fails to compile
+
+cd tests/compiletest
+if cargo run > /dev/null 2>&1; then
+    echo "test compiled with an odd BufEncoder capacity when it shouldn't"
+    exit 1
+else
+    echo "odd BufEncoder capacity failed to compile as expected"
+    exit 0
+fi

tests/compiletest/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "compiletest"
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.63.0"
+
+[dependencies]
+hex = { package = "hex-conservative", path = "../../" }

tests/compiletest/src/main.rs

@@ -0,0 +1,7 @@
+use hex::buf_encoder::BufEncoder;
+use hex::Case;
+
+fn main() { odd_buffer(); }
+
+// This should fail to compile because the capacity size is odd.
+fn odd_buffer() { let _encoder = BufEncoder::<3>::new(Case::Lower); }