getattr() should work whenever hasattr() is True

[mboes]

Description of the problem

hasattr() returns True even when for the given attribute getattr() always throws an exception. This has the unfortunate side effect that one cannot safely getattr() the value of an attribute, even when guarding it with hasattr() beforehand.

I would expect the following intuitive property to hold:

getattr(x, "foo") returns a value (does not raise an exception) if and only if hasattr(x, "foo") == True.

But since at least e5e3e91, this
does not hold.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

x = struct(a = 1)
print(dir(x))
for f in dir(x):
  if hasattr(x, "a"):
    print(getattr(x, "a", "method"))

raises an exception because hasattr(x, "to_json") is True but getattr(x, "to_json") doesn't work, even when a default value ("method") is provided.

What's the output of bazel info release?

v0.13.0

Have you found anything relevant by searching the web?

Nothing in GitHub issues.

[laurentlb]

@c-parsons, with your recent changes related to method calls, this might be easier to do.

[brandjon]

From inspection of the code, it looks like this is fixed by Alan's refactoring. hasattr checks for both annotated methods/fields and Structure fields. And getattr has supported accessing builtin methods for quite a while now.