CI: lint policy belongs on one toolchain

The MSRV bump got the floor building, and the job then failed on clippy 1.85
demanding `.and_then(seg_pos)` where clippy 1.95 is silent -- the exact mirror
of the failure fixed one commit ago, where 1.97 rejected a bare `2.0` that
1.95 accepts. Two clippy versions are not a stricter gate than one. They are a
different gate, whose contents are the union of two lint sets that can point in
opposite directions, and which no developer can reproduce without installing
every toolchain in the matrix.

So lints run once, on the pinned stable, over the whole workspace including the
GUI crate. The MSRV job proves the floor compiles and passes its tests, which
is the only claim an MSRV makes. Nothing is lost by not linting at 1.85:
clippy::incompatible_msrv runs in the lint job against the declared
rust-version and is the check that actually catches "you used an API newer than
you promised" -- it reads the floor rather than standing on it.

The borrow is dropped anyway, since it is correct under both versions;
rustfmt then pulled the expression onto one line.

Also fixed by this restructure, though it never got the chance to fail: the
MSRV job had been running `cargo fmt --check` too, and rustfmt output drifts
across versions in the same way.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -28,50 +28,18 @@ env:
   PINNED_STABLE: "1.95.0"
 
 jobs:
-  check:
-    name: fmt / clippy / test
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Install Rust (pinned MSRV)
-        uses: dtolnay/rust-toolchain@stable
-        with:
-          toolchain: "1.85"
-          components: rustfmt, clippy
-
-      - name: Cache cargo
-        uses: Swatinem/rust-cache@v2
-
-      - name: Formatting
-        run: cargo fmt --all -- --check
-
-      # The demo GUI crate (eframe/resvg) needs a newer toolchain than the pinned
-      # MSRV, so it is excluded from these MSRV-pinned workspace commands and
-      # checked on current stable in the `editor-gui` job below.
-      - name: Clippy (all targets)
-        run: cargo clippy --workspace --exclude epiphany-editor-gui --all-targets -- -D warnings
-
-      - name: Test (workspace)
-        run: cargo test --workspace --exclude epiphany-editor-gui --all-targets
-
-      - name: Doc tests
-        run: cargo test --workspace --exclude epiphany-editor-gui --doc
-
-      # Deny rustdoc warnings (broken/private intra-doc links, etc.) across the
-      # whole workspace. `RUSTFLAGS` does not cover rustdoc, so `RUSTDOCFLAGS` is
-      # set explicitly.
-      - name: Doc warnings (workspace)
-        env:
-          RUSTDOCFLAGS: -D warnings
-        run: cargo doc --workspace --exclude epiphany-editor-gui --no-deps
-
-  # The demo GUI crate, on the pinned stable rather than the MSRV: its
-  # eframe/resvg tree pulls `image`, which declares 1.88 — three releases above
-  # the workspace floor. Separate so a GUI build break is its own attributable
-  # signal, not a regression in the core crates.
-  editor-gui:
-    name: editor GUI (pinned stable)
+  # Style and lint policy runs on exactly ONE toolchain, the pinned stable.
+  #
+  # It used to run on the MSRV toolchain as well, and that is not a stricter
+  # gate — it is a different one. Two clippy versions have two lint sets, and
+  # they can disagree in opposite directions: clippy 1.85 demands
+  # `.and_then(seg_pos)` where 1.95 is silent, while 1.97 rejects a bare `2.0`
+  # that 1.95 accepts. Satisfying the union is not a quality bar, it is a
+  # coincidence, and no developer can reproduce it locally without installing
+  # every toolchain in the matrix. Lints here; the MSRV job proves the floor
+  # compiles and passes its tests, which is the only thing an MSRV can mean.
+  lint:
+    name: fmt / clippy / doc (pinned stable)
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
@@ -80,7 +48,7 @@ jobs:
         uses: dtolnay/rust-toolchain@stable
         with:
           toolchain: ${{ env.PINNED_STABLE }}
-          components: clippy
+          components: rustfmt, clippy
 
       - name: Install GUI build dependencies
         run: |
@@ -92,8 +60,72 @@ jobs:
       - name: Cache cargo
         uses: Swatinem/rust-cache@v2
 
-      - name: Clippy (GUI)
-        run: cargo clippy -p epiphany-editor-gui --all-targets -- -D warnings
+      - name: Formatting
+        run: cargo fmt --all -- --check
+
+      # The whole workspace, GUI crate included: on the pinned stable there is
+      # no toolchain reason to split it out.
+      - name: Clippy (all targets)
+        run: cargo clippy --workspace --all-targets -- -D warnings
+
+      # Deny rustdoc warnings (broken/private intra-doc links, etc.). `RUSTFLAGS`
+      # does not cover rustdoc, so `RUSTDOCFLAGS` is set explicitly.
+      - name: Doc warnings (workspace)
+        env:
+          RUSTDOCFLAGS: -D warnings
+        run: cargo doc --workspace --no-deps
+
+  # The floor, and only the floor: does the code this repository claims to
+  # support on 1.85 actually build and pass its tests there? No lints — see the
+  # `lint` job's comment.
+  check:
+    name: MSRV build + test (1.85)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust (pinned MSRV)
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: "1.85"
+
+      - name: Cache cargo
+        uses: Swatinem/rust-cache@v2
+
+      # The demo GUI crate (eframe/resvg) pulls `image`, which declares 1.88, so
+      # it cannot build at the floor and is excluded here. It is linted in
+      # `lint` and tested in `editor-gui`, both on the pinned stable.
+      - name: Test (workspace)
+        run: cargo test --workspace --exclude epiphany-editor-gui --all-targets
+
+      - name: Doc tests
+        run: cargo test --workspace --exclude epiphany-editor-gui --doc
+
+  # The demo GUI crate's tests, kept as their own job so a GUI break is its own
+  # attributable signal rather than a regression buried in the core crates. Its
+  # eframe/resvg tree pulls `image`, which declares 1.88 — three releases above
+  # the workspace floor — so it cannot run in the MSRV job. Linting for this
+  # crate lives in `lint` with the rest of the workspace.
+  editor-gui:
+    name: editor GUI tests (pinned stable)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust (pinned stable)
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: ${{ env.PINNED_STABLE }}
+
+      - name: Install GUI build dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            libxcb-render0-dev libxcb-shape0-dev libxcb-xfixes0-dev \
+            libxkbcommon-dev libssl-dev
+
+      - name: Cache cargo
+        uses: Swatinem/rust-cache@v2
 
       - name: Test (GUI)
         run: cargo test -p epiphany-editor-gui

crates/epiphany-core/src/invariants.rs

@@ -1351,11 +1351,7 @@ impl<'a> GraphIndex<'a> {
                         "tempo segments overlap in musical time".to_string(),
                     );
                 }
-                prev_end = seg
-                    .end
-                    .as_ref()
-                    .and_then(&seg_pos)
-                    .or_else(|| start.clone());
+                prev_end = seg.end.as_ref().and_then(seg_pos).or_else(|| start.clone());
                 prev_start = start;
             }
         }