view tests/test-manifest.t @ 33807:b70029f355a3

tests: verify that peer instances only expose interface members

Our abstract interfaces are more useful if we guarantee that
implementations conform to certain rules. Namely, we want to ensure
that objects implementing interfaces don't expose new public
attributes that aren't part of the interface. That way, as long as
consumers don't access "internal" attributes (those beginning with
"_") then (in theory) objects implementing interfaces can be swapped
out and everything will "just work."

We add a test that enforces our "no public attributes not part
of the abstract interface" rule.

We /could/ implement "interface compliance detection" at run-time.
However, that is littered with problems.

The obvious solutions are custom __new__ and __init__ methods.
These rely on derived types actually calling the parent's
implementation, which is no sure bet. Furthermore, __new__ and
__init__ will likely be called before instance-specific attributes
are assigned. In other words, they won't detect public attributes
set on self.__dict__. This means public attribute detection won't
be robust.

We could work around lack of robust self.__dict__ public attribute
detection by having our interfaces implement a custom __getattribute__,
__getattr__, and/or __setattr__. However, this incurs an undesirable
run-time penalty. And, subclasses could override our custom
method, bypassing the check.

The most robust solution is a non-runtime test. So that's what this
commit implements. We have a generic function for validating that an
object only has public attributes defined by abstract classes. Then,
we instantiate some peers and verify a newly constructed object
plays by the rules.

Differential Revision: https://phab.mercurial-scm.org/D339

Source bundle was generated with the following script:

# hg init
# echo a > a
# ln -s a l
# hg ci -Ama -d'0 0'
# mkdir b
# echo a > b/a
# chmod +x b/a
# hg ci -Amb -d'1 0'

  $ hg init
  $ hg -q pull "$TESTDIR/bundles/test-manifest.hg"

The next call is expected to return nothing:

  $ hg manifest

  $ hg co
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg manifest
  a
  b/a
  l

  $ hg files -vr .
           2   a
           2 x b/a (glob)
           1 l l
  $ hg files -r . -X b
  a
  l

  $ hg manifest -v
  644   a
  755 * b/a
  644 @ l

  $ hg manifest --debug
  b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644   a
  b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 755 * b/a
  047b75c6d7a3ef6a2243bd0e99f94f6ea6683597 644 @ l

  $ hg manifest -r 0
  a
  l

  $ hg manifest -r 1
  a
  b/a
  l

  $ hg manifest -r tip
  a
  b/a
  l

  $ hg manifest tip
  a
  b/a
  l

  $ hg manifest --all
  a
  b/a
  l

The next two calls are expected to abort:

  $ hg manifest -r 2
  abort: unknown revision '2'!
  [255]

  $ hg manifest -r tip tip
  abort: please specify just one revision
  [255]