ast.parse(mode='single') exception for block statements without trailing newline

[tom-pytel]

Bug report

Bug description:

I deliberated on whether to post this as its so inconsequential, but the fix (in ast.py at least, dunno about compile) is super trivial so might as well. It goes back to 3.10 at least.

>>> ast.parse('pass', mode='exec')
Module(body=[Pass()], type_ignores=[])

>>> ast.parse('pass', mode='single')
Interactive(body=[Pass()])

>>> ast.parse('if 1: pass', mode='exec')
Module(body=[If(test=Constant(value=1, kind=None), body=[Pass()], orelse=[])], type_ignores=[])

>>> ast.parse('if 1: pass', mode='single')
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    ast.parse('if 1: pass', mode='single')
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tom/work/cpython/main/cp/Lib/ast.py", line 46, in parse
    return compile(source, filename, mode, flags,
                   _feature_version=feature_version, optimize=optimize)
  File "<unknown>", line 1
    if 1: pass
SyntaxError: invalid syntax

>>> ast.parse('if 1: pass\n', mode='single')
Interactive(body=[If(test=Constant(value=1, kind=None), body=[Pass()], orelse=[])])

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

[brianschubert]

This appears to be consistent with the documented behavior. When mode="single", the docs say that source is parsed as an interactive input, which requires a trailing newline:

Input in interactive mode is parsed using the following grammar:

interactive_input ::= [stmt_list] NEWLINE | compound_stmt NEWLINE

Note that a (top-level) compound statement must be followed by a blank line in interactive mode; this is needed to help the parser detect the end of the input.

[tom-pytel]

This appears to be consistent with the documented behavior. When mode="single", the docs say that source is parsed as an interactive input, which requires a trailing newline:

A little counterintuitive that pass and x = 1; y = 2 parse without newline, but if its in the docs... What say you @picnixz, close it?

[picnixz]

Well, strictly speaking pass is not a compound statement but a simple one, but ast.parse('pass', mode='single') works. So I'm not really sure about that. I'm fine with leaving as is or rejecting ast.parse('pass', mode="single") (but I wouldn't want that honestly if it's only for consistency's sake).

WDYT @JelleZijlstra

[JelleZijlstra]

No opinion here, feels like more of a question for the parser maintainers.