ci: keep the rust caches lean and stop rebuilding for the example

.github/workflows/python-test.yml

@@ -17,7 +17,7 @@ concurrency:
 
 env:
   CARGO_TERM_COLOR: always
-  RUSTFLAGS: "-C debuginfo=1"
+  RUSTFLAGS: "-C debuginfo=line-tables-only"
   CARGO_INCREMENTAL: "0"
 
 jobs:
@@ -31,8 +31,12 @@ jobs:
       - uses: actions/checkout@v4
       - name: Setup Rust
         uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          # The rust-cache step below caches the bindings crate.
+          cache: false
       - uses: Swatinem/rust-cache@v2
         with:
+          save-if: ${{ github.ref == 'refs/heads/main' }}
           shared-key: "lance-csr-python"
           # maturin builds the bindings crate, which sits outside the workspace.
           workspaces: crates/lance-csr-python

.github/workflows/rust-test.yml

@@ -16,7 +16,7 @@ concurrency:
 
 env:
   CARGO_TERM_COLOR: always
-  RUSTFLAGS: "-C debuginfo=1"
+  RUSTFLAGS: "-C debuginfo=line-tables-only"
   RUST_BACKTRACE: "1"
   CARGO_INCREMENTAL: "0"
 
@@ -30,6 +30,8 @@ jobs:
       - uses: Swatinem/rust-cache@v2
         with:
           shared-key: "lance-csr-deps"
+          # Pull requests restore main's cache but don't save copies that crowd it out.
+          save-if: ${{ github.ref == 'refs/heads/main' }}
       - name: Install dependencies
         run: |
           sudo apt update
@@ -39,7 +41,9 @@ jobs:
       - name: Run tests
         run: cargo test --workspace
       # The Rust guide includes this example; run it so the documented code works.
+      # Run the binary the workspace test build made: `cargo run -p lance-csr` selects
+      # different features and would recompile lance-csr.
       - name: Run embedded example
-        run: cargo run -p lance-csr --example embedded_query
+        run: target/debug/examples/embedded_query
       - name: Check benchmarks
         run: cargo check -p lance-csr-benches --benches

.github/workflows/style.yml

@@ -27,6 +27,8 @@ jobs:
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           components: rustfmt
+          # Formatting compiles nothing, so there is nothing to cache.
+          cache: false
       - name: Check formatting
         run: cargo fmt --all --check
 
@@ -38,6 +40,7 @@ jobs:
       - uses: Swatinem/rust-cache@v2
         with:
           shared-key: "lance-csr-deps"
+          save-if: ${{ github.ref == 'refs/heads/main' }}
       - name: Install dependencies
         run: |
           sudo apt update