Check for executable bits that disagree with shebangs

.github/workflows/ci.yml

@@ -359,6 +359,14 @@ jobs:
       - name: gix-pack with all features (including wasm)
         run: cd gix-pack && cargo build --all-features --target "$TARGET"
 
+  check-mode:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Find scripts with mode/shebang mismatch
+        run: etc/check-mode.sh
+
   check-packetline:
     strategy:
       fail-fast: false
@@ -441,6 +449,7 @@ jobs:
       - test-32bit-cross
       - lint
       - cargo-deny
+      - check-mode
       - check-packetline
       - check-blocking
 

etc/check-mode.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+
+set -eu -o pipefail
+
+# Go to the worktree's root. (Even if the dir name ends in a newline.)
+root_padded="$(git rev-parse --show-toplevel && echo -n .)"
+root="${root_padded%$'\n.'}"
+cd -- "$root"
+
+symbolic_shebang="$(printf '#!' | od -An -ta)"
+status=0
+
+function check () {
+  local mode="$1" oid="$2" path="$3" symbolic_magic
+
+  # Extract the first two bytes (or less if shorter) and put in symbolic form.
+  symbolic_magic="$(git cat-file blob "$oid" | od -N2 -An -ta)"
+
+  # Check for inconsistency between the mode and whether `#!` is present.
+  if [ "$mode" = 100644 ] && [ "$symbolic_magic" = "$symbolic_shebang" ]; then
+    printf 'mode -x but has shebang: %q\n' "$path"
+  elif [ "$mode" = 100755 ] && [ "$symbolic_magic" != "$symbolic_shebang" ]; then
+    printf 'mode +x but no shebang: %q\n' "$path"
+  else
+    return 0
+  fi
+
+  status=1
+}
+
+# Check regular files named with a `.sh` suffix.
+while read -rd '' mode oid _stage_number path; do
+  case "$mode" in
+  100644 | 100755)
+    check "$mode" "$oid" "$path"
+    ;;
+  esac
+done < <(git ls-files -sz -- '*.sh')
+
+exit "$status"

justfile

@@ -255,6 +255,10 @@ fmt:
 find-yanked:
     cargo install --debug --locked --no-default-features --features max-pure --path .
 
+# Find shell scripts whose +x/-x bits and magic bytes (e.g. `#!`) disagree
+check-mode:
+    ./etc/check-mode.sh
+
 # Delete gix-packetline-blocking/src and regenerate from gix-packetline/src
 copy-packetline:
     ./etc/copy-packetline.sh