Add CI check for odd BufEncoder CAP

Add a test file that has an odd capacity BufEncoder.

Add a test file that has an even capacity BufEncoder.

Add a CI check that the even capacity compiles and the odd capacity
does not.

.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

contrib/compile-tests.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+
+even_capacity() {
+    cd even-capacity
+    if cargo run > /dev/null 2>&1; then
+        cd ..
+        return 0
+    else
+        cd ..
+        return 1
+    fi
+}
+
+odd_capacity() {
+    cd odd-capacity
+    if cargo run > /dev/null 2>&1; then
+        cd ..
+        return 0
+    else
+        cd ..
+        return 1
+    fi
+}
+
+# Check that an even capacity BufEncoder compiles and an odd BufEncoder capacity fails to compile
+cd tests/compiletests
+if ! even_capacity; then
+    echo "even-capacity BufEncoder failed to compile"
+    exit 1
+elif odd_capacity; then
+    echo "odd-capacity BufEncoder compiled when it should not have"
+    exit 1
+else
+    echo "BufEncoder capacity compile tests passed"
+    exit 0
+fi

tests/compiletests/even-capacity/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "even-capacity"
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.63.0"
+
+[workspace]
+
+[dependencies]
+hex = { package = "hex-conservative", path = "../../../" }

tests/compiletests/even-capacity/src/main.rs

@@ -0,0 +1,5 @@
+use hex::buf_encoder::BufEncoder;
+use hex::Case;
+
+// This should compile, ensuring that the compile error in odd-capacity is from the odd capacity.
+fn main() { let _encoder = BufEncoder::<4>::new(Case::Lower); }

tests/compiletests/odd-capacity/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "odd-capacity"
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.63.0"
+
+[workspace]
+
+[dependencies]
+hex = { package = "hex-conservative", path = "../../../" }

tests/compiletests/odd-capacity/src/main.rs

@@ -0,0 +1,6 @@
+use hex::buf_encoder::BufEncoder;
+use hex::Case;
+
+// This should fail to compile because the capacity size is odd.
+// The only difference to `even-capacity` is the capacity size.
+fn main() { let _encoder = BufEncoder::<3>::new(Case::Lower); }