Changes:
- Allow unit contracts to import and export the same signature.
- Add "invoke" contracts that will wrap the result of invoking a unit contract,
no wrapping occurs when a body contract is not specified
- Improve error messages
- Support for init-depend clauses in unit contracts.
- Fix documentation to refelct the above
- Overhaul of unit related tests
Handling init-depend clauses in unit contracts is a rather large and somewhat
non-backwards-compatible change to unit contracts. Unit contracts must now
specify at least as many initialization dependencies as the unit value being
contracted, but may include more. These new dependencies are now actually
specified in the unit wrapper so that they will be checked by compound-unit
expressions.
This commit also adds more information to the first-order-check
error messages. If a unit imports tagged signatures, previously the errror
message did not specify which tag was missing from the unit contract. Now
the tag is printed along with the signature name.
Documentation has been edited to reflect the changes to unit/c contracts
made by this commit.
Additionally this commit overhauls all tests for units and unit contracts.
Test cases now actually check that expected error messages are triggered when
checking contract, syntax, and runtime errors. Test forms now expand into uses
of rackunit's check-exn form so only test failures are reported and all tests in
a file are run on every run of the test file.
When using `compound-unit/infer` and similar, check the `link` clause
against each unit's static information for initialization dependencies.
Also, propagate dependency information in `define-compount-unit`.
