If "deriving (C)" fails, it will now, if possible, indicate which
particular field of which constructor has caused the failure. (This
fixes #8576)

When doing non-standalone deriving, annotate each individual
unsimplified constraint with its own CtOrigin. This is just the
refactoring, so the CtOrigin is still CtDeriv in each case.

This note is a summary of an explanation by SPJ to me.

That’s where all its users are...

This commit is just a refactoring, intended to make the use of
rejigConRes (which sorts out the return types of GADT-like constructors)
less delicate. The idea is that, if we perform role checking in a
second top-level pass, we can use checkValidDataCon to check for
valid return types. Previously, checking roles would force the
rejigConRes thunk before we knew that rejigConRes was safe to call!

It now reads

   Could not coerce from ‛S a’ to ‛S (NT a)’

and does not mention Coercible any more (as discussed in #8567).

just like other type errors occurring during deriving.

in comments and function names, to use less names for the same thing.

This commit was accidentally pushed.

This reverts commit 574ccfa2.

Thanks to aavogt

This is a kludge to workaround Clang's CPP lacking traditional-mode CPP

(This was reported by Kazu Yamamoto)

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

This fixes Trac #8570

This fixes #8540 (again), and simplifies matters a bit more. In
particular, I got rid of ic_sys_vars altogether.  Mostly they can just
go in ic_tythings, apart from dfuns, which are readily gettable from
the instances anyway.

See documentation in Note [Initialising the type environment for GHCi]
in TcEnv.

The runtime debugger (which has not received any love from anyone
for many years) looks wrong to me; it was failing to instantiate the
outer foralls of a variable when called from :force, which calls
cvObtainTermFromId, which calls cvObtainTerm

I simplified the code too.  But I'm flaky on how this debugger stuff
is really supposed to work, so I'm partly guessing.  Tests pass though.

I liked the idea of combining traceRunStatus and handleRunStatus, but
I think we lost a bit of clarity where traceRunStatus wants to fall
back to handleRunStatus when the breakpoint is enabled.  So I
refactored it a bit more.

as the coercions for type literals are of that role.

using deferTcSForAllEq, just like for ~ types, during canonicalization