133 lines
4.8 KiB
Python
Executable file
133 lines
4.8 KiB
Python
Executable file
#!/usr/bin/env python3
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import argparse
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import json
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import re
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import sys
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# whitespace is constrained to a single space char to prevent model "running away" in
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# whitespace. Also maybe improves generation quality?
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SPACE_RULE = '" "?'
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PRIMITIVE_RULES = {
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'boolean': '("true" | "false") space',
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'number': '("-"? ([0-9] | [1-9] [0-9]*)) ("." [0-9]+)? ([eE] [-+]? [0-9]+)? space',
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'integer': '("-"? ([0-9] | [1-9] [0-9]*)) space',
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'string': r''' "\"" (
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[^"\\] |
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"\\" (["\\/bfnrt] | "u" [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F])
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)* "\"" space ''',
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'null': '"null" space',
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}
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INVALID_RULE_CHARS_RE = re.compile(r'[^a-zA-Z0-9-]+')
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GRAMMAR_LITERAL_ESCAPE_RE = re.compile(r'[\r\n"]')
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GRAMMAR_LITERAL_ESCAPES = {'\r': '\\r', '\n': '\\n', '"': '\\"'}
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class SchemaConverter:
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def __init__(self, prop_order):
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self._prop_order = prop_order
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self._rules = {'space': SPACE_RULE}
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def _format_literal(self, literal):
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escaped = GRAMMAR_LITERAL_ESCAPE_RE.sub(
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lambda m: GRAMMAR_LITERAL_ESCAPES.get(m.group(0)), json.dumps(literal)
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)
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return f'"{escaped}"'
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def _add_rule(self, name, rule):
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esc_name = INVALID_RULE_CHARS_RE.sub('-', name)
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if esc_name not in self._rules or self._rules[esc_name] == rule:
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key = esc_name
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else:
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i = 0
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while f'{esc_name}{i}' in self._rules:
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i += 1
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key = f'{esc_name}{i}'
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self._rules[key] = rule
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return key
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def visit(self, schema, name):
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schema_type = schema.get('type')
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rule_name = name or 'root'
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if 'oneOf' in schema or 'anyOf' in schema:
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rule = ' | '.join((
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self.visit(alt_schema, f'{name}{"-" if name else ""}{i}')
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for i, alt_schema in enumerate(schema.get('oneOf') or schema['anyOf'])
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))
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return self._add_rule(rule_name, rule)
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elif 'const' in schema:
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return self._add_rule(rule_name, self._format_literal(schema['const']))
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elif 'enum' in schema:
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rule = ' | '.join((self._format_literal(v) for v in schema['enum']))
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return self._add_rule(rule_name, rule)
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elif schema_type == 'object' and 'properties' in schema:
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# TODO: `required` keyword
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prop_order = self._prop_order
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prop_pairs = sorted(
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schema['properties'].items(),
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# sort by position in prop_order (if specified) then by key
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key=lambda kv: (prop_order.get(kv[0], len(prop_order)), kv[0]),
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)
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rule = '"{" space'
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for i, (prop_name, prop_schema) in enumerate(prop_pairs):
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prop_rule_name = self.visit(prop_schema, f'{name}{"-" if name else ""}{prop_name}')
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if i > 0:
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rule += ' "," space'
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rule += fr' {self._format_literal(prop_name)} space ":" space {prop_rule_name}'
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rule += ' "}" space'
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return self._add_rule(rule_name, rule)
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elif schema_type == 'array' and 'items' in schema:
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# TODO `prefixItems` keyword
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item_rule_name = self.visit(schema['items'], f'{name}{"-" if name else ""}item')
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rule = f'"[" space ({item_rule_name} ("," space {item_rule_name})*)? "]" space'
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return self._add_rule(rule_name, rule)
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else:
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assert schema_type in PRIMITIVE_RULES, f'Unrecognized schema: {schema}'
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return self._add_rule(
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'root' if rule_name == 'root' else schema_type,
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PRIMITIVE_RULES[schema_type]
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)
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def format_grammar(self):
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return '\n'.join((f'{name} ::= {rule}' for name, rule in self._rules.items()))
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def main(args_in = None):
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parser = argparse.ArgumentParser(
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description='''
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Generates a grammar (suitable for use in ./main) that produces JSON conforming to a
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given JSON schema. Only a subset of JSON schema features are supported; more may be
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added in the future.
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''',
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)
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parser.add_argument(
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'--prop-order',
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default=[],
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type=lambda s: s.split(','),
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help='''
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comma-separated property names defining the order of precedence for object properties;
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properties not specified here are given lower precedence than those that are, and are
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sorted alphabetically
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'''
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)
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parser.add_argument('schema', help='file containing JSON schema ("-" for stdin)')
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args = parser.parse_args(args_in)
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schema = json.load(sys.stdin if args.schema == '-' else open(args.schema))
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prop_order = {name: idx for idx, name in enumerate(args.prop_order)}
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converter = SchemaConverter(prop_order)
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converter.visit(schema, '')
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print(converter.format_grammar())
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if __name__ == '__main__':
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main()
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