Fix hash calculation

This was resetting the current hash value so not calculating an
interface hash correctly, so sometimes not rebuilding when necessary.

src/Core/Hash.idr

@@ -62,7 +62,7 @@ Hashable String where
 export
 Hashable Name where
   hashWithSalt h (MN s _) = hashWithSalt h s
-  hashWithSalt h (Resolved i) = i
+  hashWithSalt h (Resolved i) = hashWithSalt h i
   hashWithSalt h n = hashWithSalt h (show n)
 
 export

src/Idris/ProcessIdr.idr

@@ -70,8 +70,6 @@ readModule top loc vis reexp imp as
          extendAs imp as syn
 
          defs <- get Ctxt
-         when top $ put Ctxt (record { importHashes $= ((as, hash) ::) } defs)
-
          modNS <- getNS
          when vis $ setVisible imp
          traverse_ (\ mimp =>
@@ -241,6 +239,12 @@ processMod srcf ttcf msg mod sourcecode
                         setNS ns
                         errs <- logTime "Processing decls" $
                                     processDecls (decls mod)
+
+                        -- Save the import hashes for the imports we just read.
+                        -- If they haven't changed next time, and the source
+                        -- file hasn't changed, no need to rebuild.
+                        defs <- get Ctxt
+                        put Ctxt (record { importHashes = hs } defs)
                         pure (Just errs))
           (\err => pure (Just [err]))