Check for dead code in CI

The build-compiler job that builds the playground now runs make dead-code
after the playground build, so new dead code fails CI. It installs
reanalyze 2.27.0, the first release that analyzes the native and the
browser build trees together, from its tag until the opam-repository
package is merged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Kbf3gLDo8mBJKpNE25WAwT
Signed-off-by: Christoph Knittel <ck@cca.io>

Author: cknitt

.github/workflows/ci.yml

@@ -275,6 +275,15 @@ jobs:
         if: matrix.build_playground
         run: opam exec -- make playground
 
+      # Runs after the playground build, whose browser-profile tree it
+      # analyzes together with the native one.
+      - name: Check for dead code
+        if: matrix.build_playground
+        run: |
+          opam pin add --yes --no-action reanalyze git+https://github.com/rescript-lang/reanalyze.git#v2.27.0
+          opam install --yes reanalyze
+          opam exec -- make dead-code
+
       - name: Test playground compiler
         if: matrix.build_playground
         run: yarn workspace playground test

changes/dead-code-ci.internal.md

@@ -0,0 +1 @@
+- Check in CI that reanalyze reports no dead code in the OCaml sources.

scripts/dead_code.sh

@@ -4,8 +4,8 @@
 # anything.
 #
 # Usage: REANALYZE=/path/to/reanalyze.exe ./scripts/dead_code.sh
-# (defaults to reanalyze.exe on PATH; needs a reanalyze that analyzes several
-# build trees together, rescript-lang/reanalyze#224)
+# (defaults to reanalyze.exe on PATH; needs reanalyze 2.27.0 or later, which
+# analyzes several build trees together: opam install reanalyze)
 
 set -euo pipefail
 cd "$(dirname "$0")/.."