Helps catch missing dependencies in dune files.

Signed-off-by: Edwin Török <[email protected]>

This will be a new library that will provide a more type-safe interface to file descriptor operations.
Useful on its own, but also for testing stdext.

Minimal dependencies, only Unix (and Alcotest for testing).

Signed-off-by: Edwin Török <[email protected]>

This will be a test framework providing QCheck generators and properties for
testing file descriptor operations.
It will try to generate:
* different kinds of file descriptors
* actual data written/read on the other end of pipes and socket pairs
* different speeds and delays on the other end to find buffering bugs
* file descriptors that are >1024 to find bugs with select

Signed-off-by: Edwin Török <[email protected]>

We are going to use type-level constraints a lot.
Try to future proof it by using the recommended compiler flag.
`ocamlc` says this about `-principal`:
> When using labelled arguments and/or polymorphic methods, this flag is required to
> ensure future versions of the compiler will be able to infer types correctly, even if internal algorithms change

Signed-off-by: Edwin Török <[email protected]>

This is not enabled by default (but bisect-ppx is nevertheless a build-time dependency)
Usage: `make coverage`

Signed-off-by: Edwin Török <[email protected]>

Lightweight wrapper using polymorphic variants to track read, write, and file kind properties on file descriptors.
We only track the property at the time the file descriptor was opened.

This prevents bugs like accidentally swapping the read and write ends of a pipe,
or attempting to run an operation on a file descriptor that would alway s fail (e.g. setting a socket timeout on a pipe)

Write tests using cram-style expect tests that the operations we expect to be forbidden by this type system
are actually forbidden.
The error messages may be compiler version dependent, so only run them on OCaml 4.14.1 for now.

Signed-off-by: Edwin Török <[email protected]>

Use the capabilities module to wrap most Unix operations needed in testing Unixext

Add a testsuite that checks that whenever the type says "never" the underlying file descriptor operation
would indeed raise an exception. This ensures that the type constraints we declare are actually correct.
The checks use unsafe operations that bypass the type layer.

Similarly check that operations that are accepted by the type system and marked as "always" in the type succeed.

Signed-off-by: Edwin Török <[email protected]>

Signed-off-by: Edwin Török <[email protected]>

Signed-off-by: Edwin Török <[email protected]>

It can be used to wrap read or write operations andobserve the data that is transferred,
and elapsed time.

It also provides 2 functions that create a file of a given kind.

We only test UNIX sockets, because socketpair doesn't support TCP sockets on Linux.

Signed-off-by: Edwin Török <[email protected]>

Signed-off-by: Edwin Török <[email protected]>