Bug report

The handling of whitespace around the argument in literal string interpolation (f-string) is unexpected when a conversion specifier (e.g. !r) is applied.

Consider

f"{None}"  # OK
f"{ None }"  # OK
f"{None!r}"  # OK
f"{ None!r }"  # SyntaxError

# details
f"{ None!r}  # OK
f"{None !r}  # OK
f"{None!r }  # SyntaxError

PEP-498 states:

Leading and trailing whitespace in expressions is ignored
For ease of readability, leading and trailing whitespace in expressions is ignored. This is a by-product of enclosing the expression in parentheses before evaluation.

I suppose that the text above may be technically accurate, but is misleading to common folk:
In the example above, None is enclosed in parentheses (None) but not None!r.

There are no mentions of whitespace in the rest of the PEP.

Formal reproducer:

> python3.11 -c 'print(f"{ None!r }")'
  File "<string>", line 1
    print(f"{ None!r }")
                       ^
SyntaxError: f-string: expecting '}'

Your environment

• CPython versions tested on: 3.8, 3.9, 3.10, 3.11a2, 3.11a7
• Operating system and architecture: Linux, MacOS