Fix 7807 (#7820)

Commit a8c7947 removed the old parser after the new one had taken
over, but the ability to use `mypy.parse` as a script for dumping
parse trees was also removed, perhaps by accident. This commit adds
that functionality back as a script under `misc/`.

This is work towards #7807. What remains is editing the wiki accordingly.

Author: goodmami

misc/dump-ast.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+
+"""
+Parse source files and print the abstract syntax trees.
+"""
+
+from typing import Tuple
+import sys
+import argparse
+
+from mypy.errors import CompileError
+from mypy.options import Options
+from mypy import defaults
+from mypy.parse import parse
+
+
+def dump(fname: str,
+         python_version: Tuple[int, int],
+         quiet: bool = False) -> None:
+    options = Options()
+    options.python_version = python_version
+    with open(fname, 'rb') as f:
+        s = f.read()
+        tree = parse(s, fname, None, errors=None, options=options)
+        if not quiet:
+            print(tree)
+
+
+def main() -> None:
+    # Parse a file and dump the AST (or display errors).
+    parser = argparse.ArgumentParser(
+        description="Parse source files and print the abstract syntax tree (AST).",
+    )
+    parser.add_argument('--py2', action='store_true', help='parse FILEs as Python 2')
+    parser.add_argument('--quiet', action='store_true', help='do not print AST')
+    parser.add_argument('FILE', nargs='*', help='files to parse')
+    args = parser.parse_args()
+
+    if args.py2:
+        pyversion = defaults.PYTHON2_VERSION
+    else:
+        pyversion = defaults.PYTHON3_VERSION
+
+    status = 0
+    for fname in args.FILE:
+        try:
+            dump(fname, pyversion, args.quiet)
+        except CompileError as e:
+            for msg in e.messages:
+                sys.stderr.write('%s\n' % msg)
+            status = 1
+    sys.exit(status)
+
+
+if __name__ == '__main__':
+    main()