Look through annotations in tyfam solving (#2677)

1. Annotations are implemented as type synonyms.
2. GHC looks through type synonyms when matching type families
3. So Clash should do the same.

Fixes #2593

(cherry picked from commit da6ee06)

Co-authored-by: Christiaan Baaij <[email protected]>

changelog/2024-02-16T16_42_52+01_00_fix2593

@@ -0,0 +1 @@
+FIXED: HDL generation fails when using multiple-hidden feature in combination with synthesis attributes [#2593](https://github.com/clash-lang/clash-compiler/issues/2593)

clash-lib/src/Clash/Core/Type.hs

@@ -2,7 +2,7 @@
   Copyright   :  (C) 2012-2016, University of Twente,
                      2016     , Myrtle Software Ltd,
                      2017     , Google Inc.
-                     2021     , QBayLogic B.V.
+                     2021-2024, QBayLogic B.V.
   License     :  BSD2 (see the file LICENSE)
   Maintainer  :  QBayLogic B.V. <[email protected]>
 
@@ -452,6 +452,10 @@ funSubst
 funSubst _   Nothing  = const Nothing
 funSubst tcm (Just s) = uncurry go
   where
+    -- AnnType cannot be matched in type-families within regular GHC (as they
+    -- are type synonyms) so it is fine to skip over them here.
+    go (AnnType _ t1) t2 = go t1 t2
+
     go (VarTy nmF) ty = case lookup nmF s of
       Nothing -> Just ((nmF,ty):s)
       -- Given, for example, the type family definition:
@@ -470,6 +474,10 @@ funSubst tcm (Just s) = uncurry go
       Just ty' | ty' `aeqType` ty -> Just s
       _ -> Nothing
 
+    -- Only look through annotations in RHS after the VarTy case, so we can
+    -- preserve annotations in the substitution created by the VarTy case above
+    go t1 (AnnType _ t2) = go t1 t2
+
     -- [Note] funSubst FunTy
     --
     -- Whenever type classes have associated types whose instances 'map' to
@@ -495,13 +503,11 @@ funSubst tcm (Just s) = uncurry go
                    , argView tcm r2 -- See [Note: Eager type families]
                    )
 
-    go ty1@(ConstTy _) ty2 =
-      -- Looks through AnnType
-      if ty1 `aeqType` ty2 then Just s else Nothing
+    go (ConstTy c1) (ConstTy c2)
+      | c1 == c2 = Just s
 
-    go ty1@(LitTy _) ty2 =
-      -- Looks through AnnType
-      if ty1 `aeqType` ty2 then Just s else Nothing
+    go (LitTy l1) (LitTy l2)
+      | l1 == l2 = Just s
 
     go _ _ = Nothing
 

tests/Main.hs

@@ -788,6 +788,7 @@ runClashTest = defaultMain $ clashTestRoot
         , outputTest "T2510" def{hdlTargets=[VHDL], clashFlags=["-DNOINLINE=OPAQUE"]}
 #endif
         , outputTest "T2542" def{hdlTargets=[VHDL]}
+        , runTest "T2593" def{hdlSim=[]}
         ] <>
         if compiledWith == Cabal then
           -- This tests fails without environment files present, which are only

tests/shouldwork/Issues/T2593.hs

@@ -0,0 +1,14 @@
+module T2593 where
+
+import Clash.Prelude
+import Clash.Annotations.SynthesisAttributes
+
+topEntity ::
+  Signal System Bit ->
+  Signal System Bit `Annotate` 'StringAttr "breaka" "me"
+topEntity dIn =
+  exposeClockResetEnable (register 0) clk rst en dIn
+ where
+   clk = clockGen
+   rst = resetGen
+   en = enableGen