Positional-only argument containing = is considered named argument if keyword accepts **named

[pekkaklarck]

If a keyword accepts a positional only argument like

def example(arg, /):
    print(arg)

using it like

Example    foo=bar
Example    arg=xxx

works fine and the keyword gets foo=bar and arg=xxx as an argument, respectively. The argument is positional-only so = has no special meaning.

If the keyword also accepts free named arguments like

def example(arg, /, **named):
    print(arg, named)

using it like

Example    foo=bar

fails like

Keyword 'example.Example' expected 1 non-named argument, got 0.

This is due to a bug in argument resolving logic where all arguments containing = are considered named if the keyword accepts free named arguments. This needs to be fixed so that positional-only arguments are excluded.

After the fix we can fix #4821 by changing the signature of the Format String keyword to template, /, *positional, **named. We also should check are there other keywords accepting **named that could get the same treatment.

[pekkaklarck]

It seems that the following change is enough to fix this, but the this needs to be tested more thoroughly:

--- a/src/robot/running/arguments/argumentresolver.py
+++ b/src/robot/running/arguments/argumentresolver.py
@@ -56,9 +56,10 @@ class NamedArgumentResolver:
 
     def resolve(self, arguments, variables=None):
         spec = self.spec
-        positional = list(arguments[:len(spec.embedded)])
+        positional_count = max(len(spec.positional_only), len(spec.embedded))
+        positional = list(arguments[:positional_count])
         named = []
-        for arg in arguments[len(spec.embedded):]:
+        for arg in arguments[positional_count:]:
             if is_dict_variable(arg):
                 named.append(arg)
             else: