Add debugPprType

We pretty-print a type by converting it to an IfaceType and
pretty-printing that.  But
 (a) that's a bit indirect, and
 (b) delibrately loses information about (e.g.) the kind
      on the /occurrences/ of a type variable

So this patch implements debugPprType, which pretty prints
the type directly, with no fancy formatting.  It's just used
for debugging.

I took the opportunity to refactor the debug-pretty-printing
machinery a little.  In particular, define these functions
and use them:

  ifPprDeubug :: SDoc -> SDOc -> SDoc
    -- Says what to do with and without -dppr-debug
  whenPprDebug :: SDoc -> SDoc
    -- Says what to do with  -dppr-debug; without is empty
  getPprDebug :: (Bool -> SDoc) -> SDoc

getPprDebug used to be called sdocPprDebugWith
whenPprDebug used to be called ifPprDebug

So a lot of files get touched in a very mechanical way

1 files changed, 3 insertions, 4 deletions

diff --git a/compiler/coreSyn/CoreLint.hs b/compiler/coreSyn/CoreLint.hs
index 7878e62c5d..92c14bc871 100644
--- a/compiler/coreSyn/CoreLint.hs
+++ b/compiler/coreSyn/CoreLint.hs
@@ -2021,10 +2021,9 @@ addMsg env msgs msg
    locs = le_loc env
    (loc, cxt1) = dumpLoc (head locs)
    cxts        = [snd (dumpLoc loc) | loc <- locs]
-   context     = sdocWithPprDebug $ \dbg -> if dbg
-                  then vcat (reverse cxts) $$ cxt1 $$
-                         text "Substitution:" <+> ppr (le_subst env)
-                  else cxt1
+   context     = ifPprDebug (vcat (reverse cxts) $$ cxt1 $$
+                             text "Substitution:" <+> ppr (le_subst env))
+                            cxt1
 
    mk_msg msg = mkLocMessage SevWarning (mkSrcSpan loc loc) (context $$ msg)