Add EOL linter action.

.github/lint_matchers.json

@@ -0,0 +1,14 @@
+{
+  "problemMatcher": [
+    {
+      "owner": "lint",
+      "pattern": [
+        {
+          "regexp": "^'([^']+)'\\s+(eol mismatch\\s-\\s.+)$",
+          "file": 1,
+          "message": 2
+        }
+      ]
+    }
+  ]
+}

.github/workflows/lint.yml

@@ -0,0 +1,20 @@
+name: Lint
+on: [push, pull_request]
+
+jobs:
+  check-eol:
+    name: Check Line Endings
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Setup Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.8'
+
+      - name: Check EOL
+        run: |
+          echo "::add-matcher::.github/lint_matchers.json"
+          python eol.py

eol.py

@@ -0,0 +1,61 @@
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License as published by
+#    the Free Software Foundation, either version 3 of the License, or
+#    (at your option) any later version.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import argparse
+import re
+import subprocess
+import sys
+
+parser = argparse.ArgumentParser()
+parser.add_argument("-f", "--fail-fast", action="store_true")
+parser.add_argument("-v", "--verbose", action="store_true")
+
+exitcode = 0
+
+if __name__ == "__main__":
+    args = parser.parse_args()
+
+    regex = re.compile(r"i\/(?P<index>\S+)\s+w\/(?P<working>\S+)\s+attr\/(?P<attribute>\S+)?(?:\s+eol=(?P<eol>\S+))?\s+(?P<path>\S+)")
+    result = subprocess.Popen(
+        ["git", "ls-files", "--eol"],
+        stdout=subprocess.PIPE,
+        text=True
+    )
+
+    # Iterate over lines returned from git... Trying to buffer the entire
+    # result of git lfs-files in a Python stream is SLOW.
+    for line in result.stdout:
+        result = regex.match(line)
+        if result is None:
+            raise RuntimeError(line)
+
+        path = result.group("path")
+        if result.group("attribute") == "-text":
+            if args.verbose:
+                print(f"'{path}'\tnot a text file")
+            continue
+
+        if eol := result.group("eol"):
+            indexEol = result.group("index")
+            workingEol = result.group("working")
+            if (eol, eol) != (indexEol, workingEol):
+                print(f"'{path}'\teol mismatch - expected: '{eol}', git index: '{indexEol}', working copy: '{workingEol}'")
+                exitcode = 1
+                if args.fail_fast:
+                    sys.exit(exitcode)
+            elif args.verbose:
+                print(f"'{path}'\tgood eols")
+        elif args.verbose:
+            print(f"'{path}'\tno defined eols")
+
+    sys.exit(exitcode)