workspace: check in Cargo.lock

This is fine as the Cargo.lock lives on the top level and is not automatically
packaged into the crates, when they are published. This guarantees us increased
CI stability and better caching.

Author: phip1611

.github/workflows/_build-rust.yml

@@ -58,9 +58,9 @@ jobs:
             ~/.cargo/registry/cache/
             ~/.cargo/git/db/
             target/
-          # We do not have a Cargo.lock here, so I hash Cargo.toml
-          key: ${{ runner.os }}-rust-${{ inputs.rust-version }}-cargo-${{ hashFiles('**/Cargo.toml') }}
-          restore-keys: ${{ runner.os }}-cargo-${{ inputs.rust-version }}
+          # Hash over Cargo.toml and Cargo.lock, as this might be copied to
+          # projects that do not have a Cargo.lock in their repository tree!
+          key: ${{ runner.os }}-rust-${{ inputs.rust-version }}-cargo-${{ hashFiles('**/Cargo.toml', '**/Cargo.lock') }}
       - run: cargo version
       - name: Build (library)
         run: cargo build --target ${{ inputs.rust-target }} --features ${{ inputs.features }}

.gitignore

@@ -1,3 +1,2 @@
 target
-Cargo.lock
 *.swp