Updating pre-parser for pipeline and local usage

.gitea/preparse.sh

@@ -1,15 +1,37 @@
 #!/usr/bin/env bash
 # Reproduces the CI "Preparse .sage files" step locally, so `ruff check` sees
 # the same generated *.sage.py files that the pipeline lints. Run this before
-# `sage --python -m ruff check --no-respect-gitignore .` to catch issues that
-# only show up in the generated output (e.g. missing trailing newlines).
+# `ruff check --no-respect-gitignore .` to catch issues that only show up in
+# the generated output.
+#
+# Uses the sage.repl.preparse.preparse_file() Python API directly rather than
+# the `sage --preparse` CLI flag: the conda-forge `sage` binary used in CI is
+# a cut-down entry point that doesn't support `--preparse` (or `--python`) at
+# all, unlike the official sagemath CLI. Whichever `python` on PATH can
+# actually `import sage.repl` is used to run it -- in CI that's the conda
+# env's own `python`; locally (official sage install) it's `sage --python`.
 #
 # The generated files are gitignored; clean them up afterwards with:
 #   git clean -x sage/ playground/
 
 set -e
 
+if command -v python >/dev/null 2>&1 && python -c "import sage.repl" >/dev/null 2>&1; then
+  run_python() { python "$@"; }
+else
+  run_python() { sage --python "$@"; }
+fi
+
 for f in $(find . -name "*.sage" -not -path "./playground/*"); do
-  sage --preparse "$f"
-  printf 'from sage.all import *  # noqa: F401,F403\n%s\n' "$(cat "${f}.py")" > "${f}.py"
+  run_python -c "
+import sys
+from sage.repl.preparse import preparse_file
+
+path = sys.argv[1]
+with open(path) as fh:
+    src = fh.read()
+with open(path + '.py', 'w') as fh:
+    fh.write('from sage.all import *  # noqa: F401,F403\n')
+    fh.write(preparse_file(src))
+" "$f"
 done