Collect build timings on GitHub CI

This will help to investigate slow builds on GitHub.

.github/workflows/linux.yml

@@ -78,6 +78,14 @@ jobs:
       - name: Unit tests
         if: ${{ inputs.unit-tests }}
         run: python3 ./mach test-unit --release --with-${{ env.LAYOUT }}
+      - name: Rename build timing
+        run: cp -r target/cargo-timings target/cargo-timings-linux-${{ env.LAYOUT }}
+      - name: Archive build timing
+        uses: actions/upload-artifact@v3
+        with:
+          name: cargo-timings
+          # Using a wildcard here ensures that the archive includes the path.
+          path: target/cargo-timings-*-${{ env.LAYOUT }}
       - name: Lockfile check
         run: ./etc/ci/lockfile_changed.sh
       - name: Package

.github/workflows/mac.yml

@@ -70,6 +70,14 @@ jobs:
         run: python3 ./mach package --release
       - name: Package smoketest
         run: ./etc/ci/macos_package_smoketest.sh target/release/servo-tech-demo.dmg
+      - name: Rename build timing
+        run: cp -r target/cargo-timings target/cargo-timings-macos-${{ env.LAYOUT }}
+      - name: Archive build timing
+        uses: actions/upload-artifact@v3
+        with:
+          name: cargo-timings
+          # Using a wildcard here ensures that the archive includes the path.
+          path: target/cargo-timings-*-${{ env.LAYOUT }}
       - name: Upload package
         uses: actions/upload-artifact@v3
         with:

.github/workflows/windows.yml

@@ -72,6 +72,14 @@ jobs:
       - name: Unit tests
         if: ${{ inputs.unit-tests }}
         run: python mach test-unit --release --with-${{ env.LAYOUT }}
+      - name: Rename build timing
+        run: cp C:\a\servo\servo\target\cargo-timings C:\a\servo\servo\target\cargo-timings-windows-${{ env.LAYOUT }} -Recurse
+      - name: Archive build timing
+        uses: actions/upload-artifact@v3
+        with:
+          name: cargo-timings
+          # Using a wildcard here ensures that the archive includes the path.
+          path: target/cargo-timings-*-${{ env.LAYOUT }}
       - name: Package
         run: python mach package --release
       - name: Upload Package

python/servo/build_commands.py

@@ -393,9 +393,7 @@ class MachCommands(CommandBase):
                         expr = "s#libdir=.*#libdir=%s#g" % gst_lib_path
                         subprocess.call(["perl", "-i", "-pe", expr, pc])
 
-        # https://internals.rust-lang.org/t/exploring-crate-graph-build-times-with-cargo-build-ztimings/10975
-        # Prepend so that e.g. `-Ztimings` (which means `-Ztimings=info,html`)
-        # given on the command line can override it
+        # Gather Cargo build timings (https://doc.rust-lang.org/cargo/reference/timings.html).
         opts = ["--timings"] + opts
 
         if very_verbose:

python/servo/testing_commands.py

@@ -245,8 +245,12 @@ class MachCommands(CommandBase):
 
         packages.discard('stylo')
 
-        if len(packages) > 0 or len(in_crate_packages) > 0:
-            args = []
+        # Return if there is nothing to do.
+        if len(packages) == 0 and len(in_crate_packages) == 0:
+            return 0
+
+        # Gather Cargo build timings (https://doc.rust-lang.org/cargo/reference/timings.html).
+        args = ["--timings"]
         for crate in packages:
             args += ["-p", "%s_tests" % crate]
         for crate in in_crate_packages:
@@ -256,13 +260,12 @@ class MachCommands(CommandBase):
         if nocapture:
             args += ["--", "--nocapture"]
 
-            err = self.run_cargo_build_like_command("bench" if bench else "test",
+        return self.run_cargo_build_like_command(
+            "bench" if bench else "test",
             args,
             env=self.build_env(test_unit=True),
             with_layout_2020=with_layout_2020,
             **kwargs)
-            if err:
-                return err
 
     @Command('test-content',
              description='Run the content tests',