Rank keys so far could be of any type as long as it was
yaml-serializable, however this would introduce problems down the
line if a Location contained for example array or mapping.
This commit restricts the type of keys to only scalars and enums,
to limit the chance that a key serializes in an invalid location.
A step's artifacts now include singleTargetFilename, which gives a
suggested filename to use when a single element is extracted from the
underlying container.
This commit introduces some changes to how the revng pipeline handles
serializing to disk. Specificaly:
* Pipeline globals (specifically model.yml) are better handled if they
are in a subdirectory. They are now saved in the "context"
subdirectory.
* In python:revng.api the pipeline is serialized whenever there is a
non-reproducible change to the state (e.g. binary upload or model
change).
In the case of analyses this is done conservatively by checking that
the diff produced is not empty.
* The logic for computing a step's subdirectory has been moved to the
pipeline runner, consequently if a step is asked to serialize it
will not create any subdirectories.
* Functionality for saving a single step/context has been exposed in
Pipeline C.
* Finally, all path concatenations are now handled by
llvm::sys::path::append, for extra os-agnosticism.
We need to prevent stub kinds used just to represent dead elements to be
displayed in the GUI and CL.
We do so by introducing a DeadKind which expands their targets to the
empty list.
Add a new key to a Step, named Artifacts. If present, it indicates that
the step has a "default" Kind and Container that can be easily retrieved
without explicitly specifying either when producing an artifact.
Add additional field MIMEType to Container.
This allows API consumers to know at runtime how to treat the data
within a container without any prior knowledge.
Adds missing API functions to PipelineC that will be needed by the
GraphQL API:
* Kinds enumeration
* Get Rank and parent of a Kind
* Enumerate and inspect Ranks
* Get a Step's parent
Included are some docstring fixes
Alessandro Di Federico