Smarter HsType pretty-print for promoted datacons

Fix Trac #15898, by being smarter about when to print
a space before a promoted data constructor, in a HsType.
I had to implement a mildly tiresome function
    HsType.lhsTypeHasLeadingPromotionQuote
It has multiple cases, of course, but it's very simple.

The patch improves the error-message output in a bunch of
cases, and (to my surprise) actually fixes a bug in the
output of T14343 (Trac #14343), thus

  -  In the expression: _ :: Proxy '('( 'True,  'False),  'False)
  +  In the expression: _ :: Proxy '( '( 'True, 'False), 'False)

I discovered that there were two copies of the PromotionFlag
type (a boolean, with helpfully named data cons), one in
IfaceType and one in HsType.  So I combined into one,
PromotionFlag, and moved it to BasicTypes.  That's why
quite a few files are touched, but it's all routine.

1 files changed, 11 insertions, 0 deletions

diff --git a/compiler/utils/Binary.hs b/compiler/utils/Binary.hs
index a38af74efe..63efd14a5b 100644
--- a/compiler/utils/Binary.hs
+++ b/compiler/utils/Binary.hs
@@ -945,6 +945,17 @@ instance Binary LeftOrRight where
                    0 -> return CLeft
                    _ -> return CRight }
 
+instance Binary PromotionFlag where
+   put_ bh NotPromoted = putByte bh 0
+   put_ bh IsPromoted  = putByte bh 1
+
+   get bh = do
+       n <- getByte bh
+       case n of
+         0 -> return NotPromoted
+         1 -> return IsPromoted
+         _ -> fail "Binary(IsPromoted): fail)"
+
 instance Binary Fingerprint where
   put_ h (Fingerprint w1 w2) = do put_ h w1; put_ h w2
   get  h = do w1 <- get h; w2 <- get h; return (Fingerprint w1 w2)