rust: introduce a workspace-hack package

Introduce a workspace-hack package, managed by hakari, in order to
reduce excessive compiling.

.config/hakari.toml

@@ -0,0 +1,31 @@
+# This file contains settings for `cargo hakari`.
+# See https://docs.rs/cargo-hakari/latest/cargo_hakari/config for a full list of options.
+
+hakari-package = "workspace-hack"
+
+# Format for `workspace-hack = ...` lines in other Cargo.tomls. Requires cargo-hakari 0.9.8 or above.
+dep-format-version = "1"
+
+# Setting workspace.resolver = "2" in the root Cargo.toml is HIGHLY recommended.
+# Hakari works much better with the new feature resolver.
+# For more about the new feature resolver, see:
+# https://blog.rust-lang.org/2021/03/25/Rust-1.51.0.html#cargos-new-feature-resolver
+resolver = "2"
+
+# Add triples corresponding to platforms commonly used by developers here.
+# https://doc.rust-lang.org/rustc/platform-support.html
+platforms = [
+    # "x86_64-unknown-linux-gnu",
+    # "x86_64-apple-darwin",
+    # "x86_64-pc-windows-msvc",
+]
+
+# Write out exact versions rather than a semver range. (Defaults to false.)
+# exact-versions = true
+
+output-single-feature = true
+
+[final-excludes]
+workspace-members = [
+    "x",
+]

.github/workflows/rust.yml

@@ -46,8 +46,16 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions-rs/toolchain@v1
       - uses: bmwill/rust-cache@v1 # Fork of 'Swatinem/rust-cache' which allows caching additional paths
+      - name: Install cargo-hakari, and cache the binary
+        uses: baptiste0928/cargo-install@v1
+        with:
+          crate: cargo-hakari
+          locked: true
       - run: scripts/license_check.sh
       - run: cargo xlint
+      - run: |
+          cargo hakari generate --diff  # workspace-hack Cargo.toml is up-to-date
+          cargo hakari manage-deps --dry-run  # all workspace crates depend on workspace-hack
 
   test:
     needs: diff
@@ -127,10 +135,19 @@ jobs:
         with:
           crate: cargo-udeps
           locked: true
+      - name: Install cargo-hakari, and cache the binary
+        uses: baptiste0928/cargo-install@v1
+        with:
+          crate: cargo-hakari
+          locked: true
       # Normally running cargo-udeps requires use of a nightly compiler
       # In order to have a more stable and less noisy experience, lets instead
       # opt to use the stable toolchain specified via the 'rust-toolchain' file
       # and instead enable nightly features via 'RUSTC_BOOTSTRAP'
       - name: run cargo-udeps
-        run: RUSTC_BOOTSTRAP=1 cargo udeps
+        run: |
+          # First we need to disable the workspace-hack package
+          cargo hakari disable
+          cargo hakari remove-deps -y
+          RUSTC_BOOTSTRAP=1 cargo udeps