Fix bug: source_from_ast should consider the garbage at the end

lambdex/utils/ast.py

@@ -119,7 +119,19 @@ def ast_from_source(source, keyword: str):
  source_lines = ['\n'] * lnum + inspect.getblock(lines[lnum:])
  source = ''.join(source_lines)
 
- return ast.parse(source).body[0]
+ # Some garbage may still remain at the end, we alternatively try compiling
+ # and popping the last character until the source is valid.
+ exc = None
+ original_source = source
+ while source:
+ try:
+ return ast.parse(source).body[0]
+ except SyntaxError as e:
+ source = source[:-1]
+ exc = e
+ else:
+ # This should never happen
+ raise RuntimeError('cannot parse the snippet into AST:\n{}'.format(original_source)) from exc
 
 
 def recursively_set_attr(node: ast.AST, attrname: str, value):