[mypyc] Raise "non-trait base must be first..." error less frequently #14468
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ichard26
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This is a draft now because I'd like to also add a check for traits subclassing concrete classes (raising an error if so). It's almost ready to be pushed, but I need to finish the commandline tests and write a good commit message. |
It would raise even if there were only non-trait bases, leading to this
slightly confusing situation:
class A: pass
class B: pass
class C(A, B): pass # E: Non-trait bases must appear first in parent list
# E: Multiple inheritance is not supported (except for traits)
Now the bases must include a non-trait *and* the first base must be a
trait to error. This leads to some false-negative when there's more
than one non-trait base, but in that case, it's better to only tell the
user multiple inheritance is not supported.
ichard26
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Turns out that traits are allowed to subclass concrete classes as long as the MRO is linear (ie. no multiple inheritance just like for regular native classes). |
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It would raise even if there were only non-trait bases, leading to this slightly confusing situation:
Now the bases must include a non-trait and the first base must be a trait to error. This leads to some false-negatives when there's more than one non-trait base, but in that case, it's better to only tell the user that multiple inheritance is not supported.
See also: mypyc/mypyc#826 (comment)