CMAKE: Add rule for generating options file for doc.

cmake-scripts/docgen.cmake

@@ -100,3 +100,13 @@ foreach(ASY_DOC_FILE_PREFIX ${ASY_DOC_FILE_PREFIXES})
     )
     list(APPEND ASY_DOC_PDF_FILES ${ASY_DOC_FILE_OUTPUT})
 endforeach()
+
+
+# options file
+add_custom_command(
+        OUTPUT ${ASY_TEX_BUILD_ROOT}/options
+        DEPENDS asy ${ASY_DOC_ROOT}/gen-asy-options-file.py
+        COMMAND ${PY3_INTERPRETER} ${ASY_DOC_ROOT}/gen-asy-options-file.py
+            --asy-executable=$<TARGET_FILE:asy>
+            --output-file=${ASY_TEX_BUILD_ROOT}/options
+)

doc/gen-asy-options-file.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+import argparse
+import subprocess
+import subprocess as sp
+
+
+def parse_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--asy-executable", type=str, default="asy")
+    parser.add_argument("--output-file", type=str, required=True)
+    return parser.parse_args()
+
+
+def main():
+    args = parse_args()
+    asy_output = sp.run(
+        [args.asy_executable, "-h"],
+        check=True,
+        stderr=subprocess.STDOUT,
+        stdout=subprocess.PIPE,
+        text=True,
+    )
+
+    with open(args.output_file, "w", encoding="utf-8") as f:
+        for line in asy_output.stdout.splitlines():
+            stripped_lines = line.strip()
+            if (
+                stripped_lines.startswith("Asymptote")
+                or stripped_lines.startswith("http")
+                or stripped_lines.startswith("Usage:")
+            ):
+                continue
+            f.write(line)
+            f.write("\n")
+
+
+if __name__ == "__main__":
+    main()