Make derived names deterministic

The names of auxiliary bindings end up in the interface file, and since uniques
are nondeterministic, we end up with nondeterministic interface files.

This uses the package and module name in the generated name, so I believe it
should avoid problems from #7947 and be deterministic as well.

The generated names look like this now:

  `$cLrlbmVwI3gpI8G2E6Hg3mO`

and with `-ppr-debug`:

  `$c$aeson_70dylHtv1FFGeai1IoxcQr$Data.Aeson.Types.Internal$String`.

Reviewed By: simonmar, austin, ezyang

Differential Revision: https://phabricator.haskell.org/D1133

GHC Trac Issues: #4012

1 files changed, 50 insertions, 1 deletions

diff --git a/compiler/utils/Encoding.hs b/compiler/utils/Encoding.hs
index c8dcea24a7..712de6ca82 100644
--- a/compiler/utils/Encoding.hs
+++ b/compiler/utils/Encoding.hs
@@ -25,11 +25,16 @@ module Encoding (
 
         -- * Z-encoding
         zEncodeString,
-        zDecodeString
+        zDecodeString,
+
+        -- * Base62-encoding
+        toBase62,
+        toBase62Padded
   ) where
 
 import Foreign
 import Data.Char
+import qualified Data.Char as Char
 import Numeric
 import GHC.Exts
 
@@ -385,3 +390,47 @@ maybe_tuple _                = Nothing
 count_commas :: Int -> String -> (Int, String)
 count_commas n (',' : cs) = count_commas (n+1) cs
 count_commas n cs         = (n,cs)
+
+
+{-
+************************************************************************
+*                                                                      *
+                        Base 62
+*                                                                      *
+************************************************************************
+
+Note [Base 62 encoding 128-bit integers]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Instead of base-62 encoding a single 128-bit integer
+(ceil(21.49) characters), we'll base-62 a pair of 64-bit integers
+(2 * ceil(10.75) characters).  Luckily for us, it's the same number of
+characters!
+-}
+
+--------------------------------------------------------------------------
+-- Base 62
+
+-- The base-62 code is based off of 'locators'
+-- ((c) Operational Dynamics Consulting, BSD3 licensed)
+
+-- | Size of a 64-bit word when written as a base-62 string
+word64Base62Len :: Int
+word64Base62Len = 11
+
+-- | Converts a 64-bit word into a base-62 string
+toBase62Padded :: Word64 -> String
+toBase62Padded w = pad ++ str
+  where
+    pad = replicate len '0'
+    len = word64Base62Len - length str -- 11 == ceil(64 / lg 62)
+    str = toBase62 w
+
+toBase62 :: Word64 -> String
+toBase62 w = showIntAtBase 62 represent w ""
+  where
+    represent :: Int -> Char
+    represent x
+        | x < 10 = Char.chr (48 + x)
+        | x < 36 = Char.chr (65 + x - 10)
+        | x < 62 = Char.chr (97 + x - 36)
+        | otherwise = error "represent (base 62): impossible!"