Make CI Clippy static analysis checks more robust

I have identified two potential improvements for how we perform static analysis
on our code in our CI pipeline:

- The `giraffate/clippy-action` we currently use has not been updated to Node
  20, and GitHub has repeatedly indicated that they will phase out actions that
  do not support the latest Node versions. Despite my efforts to help with the
  update by submitting a pull request upstream, it has been ignored for months
  despite its perceived ease of review, raising concerns about the ongoing
  maintenance of the action. This situation suggests we should explore
  alternative methods for integrating Clippy with GitHub's UI.
- As evidenced by PR 632, thoroughly testing Rust crates for every possible
  feature combination is often overlooked due to the tedious nature of the task.
  Our current CI setup only checks two feature combinations, which is far from
  comprehensive.

To address the first improvement, these changes drop `clippy-action` entirely in
favor of utilizing GitHub's native CodeQL SARIF (Static Analysis Results
Interchange Format) file integration. Since Clippy cannot directly output lints
in SARIF, `clippy-sarif` is used to convert Clippy's JSON output to SARIF.
Additionally, `sarif-fmt` is added to turn SARIF into a human-friendly display
format in the workflow run logs.

For the second improvement, let's use `cargo hack` with the `--feature-powerset`
flag to run Clippy for every possible feature combination. This approach strikes
a good balance between CI runtime and thoroughness, as the number of feature
combinations grows superlinearly with the number of features: running `cargo
nextest` for every powerset element would lead to excessively long CI times.

.github/workflows/oxipng.yml

@@ -102,25 +102,33 @@ jobs:
       - name: Install nextest
         uses: taiki-e/install-action@nextest
 
+      - name: Install cargo-hack
+        if: matrix.target == 'x86_64-unknown-linux-gnu'
+        uses: taiki-e/install-action@cargo-hack
+
+      - name: Install clippy-sarif
+        if: matrix.target == 'x86_64-unknown-linux-gnu'
+        uses: taiki-e/install-action@v2
+        with:
+          tool: clippy-sarif
+
+      - name: Install sarif-fmt
+        if: matrix.target == 'x86_64-unknown-linux-gnu'
+        uses: taiki-e/install-action@v2
+        with:
+          tool: sarif-fmt
+
       - name: Run rustfmt
         if: matrix.target == 'x86_64-unknown-linux-gnu'
         run: cargo fmt --check
 
-      - name: Run Clippy (no default features)
+      - name: Run Clippy for all feature combinations
         if: matrix.target == 'x86_64-unknown-linux-gnu'
-        uses: giraffate/clippy-action@v1
-        with:
-          clippy_flags: --no-deps --all-targets --no-default-features -- -D warnings
-          reporter: github-check
-          fail_on_error: true
-
-      - name: Run Clippy (all features)
-        if: matrix.target == 'x86_64-unknown-linux-gnu'
-        uses: giraffate/clippy-action@v1
-        with:
-          clippy_flags: --no-deps --all-targets --all-features -- -D warnings
-          reporter: github-check
-          fail_on_error: true
+        run: >
+          cargo hack clippy --no-deps --all-targets --feature-powerset --exclude-features sanity-checks --message-format=json -- -D warnings
+          | clippy-sarif
+          | tee clippy-results.sarif
+          | sarif-fmt
 
       - name: Run tests
         run: |
@@ -145,6 +153,13 @@ jobs:
             target/${{ env.CARGO_BUILD_TARGET }}/release/oxipng
             target/${{ env.CARGO_BUILD_TARGET }}/release/oxipng.exe
 
+      - name: Upload analysis results to GitHub
+        uses: github/codeql-action/upload-sarif@v3
+        if: always() && matrix.target == 'x86_64-unknown-linux-gnu'
+        with:
+          sarif_file: clippy-results.sarif
+          category: clippy
+
   msrv-check:
     name: MSRV check
 

src/main.rs

@@ -329,10 +329,10 @@ fn parse_opts_into_struct(
         if let Some(iterations) = NonZeroU8::new(15) {
             opts.deflate = Deflaters::Zopfli { iterations };
         }
-    } else if let Deflaters::Libdeflater { compression } = &mut opts.deflate {
-        if let Some(x) = matches.get_one::<i64>("compression") {
-            *compression = *x as u8;
-        }
+    } else if let (Deflaters::Libdeflater { compression }, Some(x)) =
+        (&mut opts.deflate, matches.get_one::<i64>("compression"))
+    {
+        *compression = *x as u8;
     }
 
     #[cfg(feature = "parallel")]

src/rayon.rs

@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 pub mod prelude {
     pub use super::*;
 }