Parse bare words with hyphens inside containers as strings

[LeSingh1]

Summary

Fixes #561.

A bare word containing a hyphen, such as foo-bar, parses as an AST BinOp (Name - Name). When such a word appeared inside a container like a tuple or list, _LiteralEval only rewrote bare ast.Name nodes into strings. The BinOp survived, ast.literal_eval failed on it, and the whole input collapsed back to a raw string.

DefaultParseValue('(foo-bar, baz)')  ->  '(foo-bar, baz)'   # whole thing a string

Expected: ('foo-bar', 'baz').

Fix

When walking the AST, also detect a bare-word BinOp (a BinOp whose leaves are all ast.Name) and replace it with its original source text as a string, using ast.get_source_segment. BinOps that contain numbers are deliberately left untouched so existing behavior is preserved.

After the change:

'(foo-bar, baz)'  ->  ('foo-bar', 'baz')
'[a-b-c, d]'      ->  ['a-b-c', 'd']
'{a: foo-bar}'    ->  {'a': 'foo-bar'}
'1+1'             ->  '1+1'        (unchanged)
'[1+1]'           ->  '[1+1]'      (unchanged)
'2017-10-10'      ->  '2017-10-10' (unchanged)

ast.get_source_segment is available on Python 3.8+, consistent with the existing 3.8 version guard in this file.

Tests

Added testDefaultParseValueBareWordsWithHyphens to fire/parser_test.py. It fails before the change and passes after. Full suite:

$ python -m pytest fire/parser_test.py -q
21 passed

core_test.py and fire_test.py also pass.

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Developed with AI assistance and verified locally as described above.