Improve canister_tests caching (#832)

This makes the canister_tests job faster by improving caching. On main,
tests can take up to 40minutes to run, and are now down to 5 or 10mn
depdending on the cache state.

In particular, this adds more file to be cached (including files
recently introduced by cargo which most likely broke the caching) and
splits some steps into more steps for better visibility re. where time
is spent.

.github/workflows/canister-tests.yml

@@ -157,27 +157,32 @@ jobs:
   # (note: this runs _all_ cargo tests)
   canister-tests:
     runs-on: ${{ matrix.os }}
-    needs:
-      - docker-build
+    needs: docker-build
     strategy:
       matrix:
         os: [ ubuntu-latest, macos-latest ]
     steps:
       - uses: actions/checkout@v2
 
+      - uses: ./.github/actions/bootstrap
+
+      # Rustup only installs cargo on the first call, so we use a dedicated step to get a good idea of how
+      # time is spent in each step separately
+      - run: cargo check --help
+
         # NOTE: the top-level crate "canister_tests" still gets recompiled (~4mn)
         # due to the mtime changing on the checkout. Can be worked around by storing
         # the original mtime in the cache and by hashing all of src/canister_tests
         # (and then restoring the mtime).
       - uses: actions/cache@v2
         with:
+          # note on paths: we include the whole ~/.cargo/. (as opposed to juse .cargo/git, etc) because cargo stores crate
+          # data as .crates(2?).{json,toml} without which the whole cache is invalidated. We may accumulate unnecessary
+          # stuff but the cache is anyway invalidated on every toolchain update.
           path: |
-            ~/.cargo/registry
-            ~/.cargo/git
+            ~/.cargo
             target
-          key: ${{ runner.os }}-cargo-${{ hashFiles('src/**/Cargo.lock', 'rust-toolchain.toml') }}
-
-      - uses: ./.github/actions/bootstrap
+          key: ${{ runner.os }}-cargo-${{ hashFiles('src/**/Cargo.lock', 'rust-toolchain.toml') }}-2
 
       - name: Create fake assets
         run : |
@@ -195,6 +200,11 @@ jobs:
           name: internet_identity_test.wasm
           path: .
 
+      # We split the test build and run so that it's clear from the GHA steps how long each took
+      - name: Build Tests
+        shell: bash
+        run: cargo build --tests --release --package canister_tests
+
       - name: Run Tests
         shell: bash
         run: |
@@ -203,8 +213,7 @@ jobs:
           # PRs that used to be green may become red (if the new release broke something). While this is not CI best practice, it's
           # a relatively small price to pay to make sure PRs are always tested against the latest release.
           curl -sSL https://github.com/dfinity/internet-identity/releases/latest/download/internet_identity_test.wasm -o internet_identity_previous.wasm
-          # the "rand" features are needed for the captcha crate to compile
-          cargo test --release --all-targets --features 'rand/std,rand/std_rng'
+          cargo test --release --package canister_tests
         env:
           RUST_BACKTRACE: 1