Fix pow and unary operators order

[krepysh]

Change order of evaluating expressions with pow by Parser.

• fixes Negative number raised to even power gives negative result if exponent is a variable #1720
• fixes Bug with right-left associativity of exponent #1722

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[davidism]

The changelog entry should be much clearer on what is changing since this affects how these expressions are evaluated.

[bart-nouveau]

There is still one bug pointed out in #1720 that would not be fixed by this pull request:

expression: '(-1) ** x'
jinja_output: '-1'
python_output: 1

minimal reproducible example

from jinja2 import Environment
env = Environment()
expression = '(-1) ** x'
env.globals = {"x": 2}
jinja_output = env.from_string(f"{{{{ {expression} }}}}").render()
python_output = str(eval(f"{expression}",env.globals))
assert python_output == jinja_output

suggested fix

One possible fix could be to modify the _make_binop function here as follows:

            self.write("(")
            self.visit(node.left, frame)
            self.write(f" {op} ")
            self.visit(node.right, frame)

changed into:

            self.write("((")
            self.visit(node.left, frame)
            self.write(")")
            self.write(f" {op} ")
            self.visit(node.right, frame)

[bart-nouveau]

In order to verify if issue #1720 is fixed, I would add the following tests:

    def test_pow_negative_base(self, env):
        tmpl = env.from_string("{{ (- 1) ** 2 }}")
        assert tmpl.render() == "1"

    def test_pow_negative_base_variable_exponent(self, env):
        tmpl = env.from_string("{{ (- 1) ** x }}", {"x": 2})
        assert tmpl.render() == "1"

    def test_negative_pow_variable_exponent(self, env):
        tmpl = env.from_string("{{ - 1 ** x }}", {"x": 2})
        assert tmpl.render() == "-1"

All the tests seems to pass adding the change suggested here

[krepysh]

@davidism, should I remove this outdated explanation? Or it will be better to leave it here in order to keep history in docs?

[bart-nouveau]

It's ok for me, it fixes issues :issue:1720 :issue:`1722