For Python before 3.6, `path.resolve()` could not take the `strict`
keyword argument.  Linting on such Python versions will raise an unnecessary
issue given the check present.  As such, quieten that lint.  Unfortunately
this ends up making the line quite long (though not too long).

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

The correct file path was computed but never returned.  This was
never caught because of a test missing consumption of one of its
parameters.  This commit resolves the bug mentioned in #722 leaving
the test to be amended by a future commit.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

This braino would mean that we'd fail to raise the right exception
if we failed to find the right project object when unpickling the
yaml cache.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

The imports of _cachekey and utils were unused.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

Unfortunately elements don't override `__init__` in general, so
we have to quieten pylint here.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

Where we have conditions of the form `var == foo or var == bar` it
can be simplified to `var in (foo, bar)` which pylint prefers.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

Unfortunately pylint can't understand that we'll always use subclasses
of Element and as such complains of a no-return function (`assemble()`)
having its return value used.  This quietens that warning.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

Pylint recommends the use of dict.get() rather than a multi-line if
statement for handling optional keyword arguments.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

A number of times, abstract methods are called which pylint cannot
possibly understand will only ever happen in subclasses which implement
the abstract methods.  This silences those specific warnings

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

Remove `source_kind` as it was unused.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

Remove the `context` variable which was unused.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

We use `preexec_fn` in our use of Popen.  Since there are threads
in the codebase, this is not necessarily safe.  However we go to
great lengths to ensure that the main process doesn't spawn threads
(they're used in gRPC a lot) and so it should be safe for our use.
As such, we disable the lint here.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

The imports of `stat` and `S_ISDIR` from `stat` should be grouped to
satisfy pylint.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

The pylint report dislikes the superfluous parens which used to
be here in this assert.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

The pylint tool is unable to understand that the abstract methods
in the artifact cache will only be called when there's concrete
implementations behind them.  Silence the lint errors for these
specific calls.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>