symbolic: Remove redundant unwrapping/rewrapping of register struct

There was a lot of redundant unwrapping and re-wrapping of the
assignment of `TypeRepr`s to the architecture register context into and
out of a `StructRepr`. Remove this.

Also, add an hlint configuration file to help avoid this in the future,
and a Github Actions workflow to enforce this in CI.

.github/workflows/lint.yml

@@ -0,0 +1,23 @@
+name: lint
+on:
+  push:
+    branches: [master, "release-**"]
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  lint:
+    runs-on: ubuntu-24.04
+    name: lint
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: false
+
+      - shell: bash
+        run: |
+          curl --location -o hlint.tar.gz \
+            https://github.com/ndmitchell/hlint/releases/download/v3.8/hlint-3.8-x86_64-linux.tar.gz
+          tar xvf hlint.tar.gz
+
+          (cd symbolic/; ../hlint-3.8/hlint src test)

symbolic/.hlint.yaml

@@ -0,0 +1,9 @@
+# HLint's default suggestions are opinionated, so we disable all of them by
+# default and enable just a small subset we can agree on.
+
+- ignore: {}  # ignore all
+
+- error:
+    name: Use crucGenRegStructType
+    lhs: "Lang.Crucible.Types.StructRepr (Data.Macaw.Symbolic.CrucGen.crucArchRegTypes x)"
+    rhs: 'Data.Macaw.Symbolic.CrucGen.crucGenRegStructType x'

symbolic/src/Data/Macaw/Symbolic.hs

@@ -333,8 +333,7 @@ mkCrucRegCFG :: forall arch ids
                 -- ^ Action to run
             -> IO (CR.SomeCFG (MacawExt arch) (EmptyCtx ::> ArchRegStruct arch) (ArchRegStruct arch))
 mkCrucRegCFG archFns halloc nm action = do
-  let crucRegTypes = crucArchRegTypes archFns
-  let macawStructRepr = C.StructRepr crucRegTypes
+  let macawStructRepr = CG.crucGenRegStructType archFns
   let argTypes = Empty :> macawStructRepr
   h <- C.mkHandle' halloc nm argTypes macawStructRepr
   Some (ng :: NonceGenerator IO s) <- newIONonceGenerator
@@ -496,7 +495,7 @@ mkParsedBlockRegCFG archFns halloc posFn b = crucGenArchConstraints archFns $ do
     let entryAddr = M.pblockAddr strippedBlock
 
     -- Get type for representing Machine registers
-    let regType = C.StructRepr (crucArchRegTypes archFns)
+    let regType = CG.crucGenRegStructType archFns
     let entryPos = posFn entryAddr
     -- Create Crucible "register" (i.e. a mutable variable) for
     -- current value of Macaw machine registers.
@@ -683,7 +682,7 @@ mkBlockSliceRegCFG archFns sliceFns halloc posFn entry body0 terms retEdges_ = c
   where
     entryAddr = M.pblockAddr entry
     entryPos = posFn entryAddr
-    archRegTy = C.StructRepr (crucArchRegTypes archFns)
+    archRegTy = CG.crucGenRegStructType archFns
     -- Addresses of blocks marked as terminators
     termAddrs = S.fromList (fmap M.pblockAddr terms)
     retEdges = Map.fromListWith S.union [(src, S.singleton tgt) | (src, tgt) <- retEdges_]
@@ -809,7 +808,7 @@ mkBlockPathRegCFG arch_fns halloc pos_fn blocks =
     let block_path = first_blocks ++ [last_block]
 
     -- Get type for representing Machine registers
-    let arch_reg_struct_type = C.StructRepr $ crucArchRegTypes arch_fns
+    let arch_reg_struct_type = CG.crucGenRegStructType arch_fns
     let entry_pos = pos_fn entry_addr
     -- Create Crucible "register" (i.e. a mutable variable) for
     -- current value of Macaw machine registers.
@@ -908,7 +907,7 @@ mkFunRegCFG archFns halloc nm posFn fn = crucGenArchConstraints archFns $ do
     -- Get list of blocks
     let blockList = Map.elems (fn^.M.parsedBlocks)
     -- Get type for representing Machine registers
-    let regType = C.StructRepr (crucArchRegTypes archFns)
+    let regType = CG.crucGenRegStructType archFns
     let entryPos = posFn entryAddr
     -- Create Crucible "register" (i.e. a mutable variable) for
     -- current value of Macaw machine registers.
@@ -1360,8 +1359,7 @@ runCodeBlock
           (C.RegEntry sym (ArchRegStruct arch)))
 runCodeBlock bak archFns archEval halloc initMem mmConf g regStruct = do
   mvar <- MM.mkMemVar "macaw:codeblock_llvm_memory" halloc
-  let crucRegTypes = crucArchRegTypes archFns
-  let macawStructRepr = C.StructRepr crucRegTypes
+  let macawStructRepr = CG.crucGenRegStructType archFns
 
   let ctx :: C.SimContext (MacawSimulatorState sym) sym (MacawExt arch)
       ctx = let fnBindings = C.insertHandleMap (C.cfgHandle g)