I'm beginning to realise why I didn't do the `toString` overriding way
back when. Thankfully, now that all of our tests are in the same place,
this is actually not a terrible ordeal.
This commit renames the files relating to the diagnostic query that produces information on the number of files extracted. The files have been renamed from "SuccessfullExtractedFiles.*" to "ExtractedFiles.*". All related tests and test files have been renamed too.
The `@tags` and `@id` attributes of the queries have been left untouched, consistent with the `@tags` and `@id` for similar queries in other languages.
Or, more generally, any copy step, as these presumably do not preserve
object identity.
(Arguably, `copy` could still be susceptible to interior mutability, but
I think that's outside the scope of this query anyway.)
There are two issues with `deepcopy` here. Firstly, the `deepcopy` function itself
has a mutable default value in its parameter `_nil` (set to the empty list by default).
Now, this value is never actually returned from `deepcopy`, as it is only used as a
sentinel, but our analysis is not clever enough to see this. Thus, it thinks that this
mutable default is returned, and hence the result of any call to `deepcopy` is a
potential source.
To remedy this, I opted to simply exclude all sources that originate from within the
standard library. It is very unlikely for any of the sources in the standard library
to be legit.
Secondly, `deepcopy` -- by virtue of being a function that we model as preserving
values -- admits data-flow through its calls, but this is not correct for the mutable
default query, as it is here the _identity_ of the default value in question that is
important. Thus, we get spurious flow through `deepcopy` for this specific query.
Moves the existing tests into the `ModificationOfParameterWithDefault` subdirectory
which already contained a bunch more tests. In the process, I also removed some
duplicated test cases.
