[ fix ] case spliting under implicit/auto parameter

src/TTImp/Interactive/CaseSplit.idr

@@ -197,7 +197,7 @@ newLHS : {auto c : Ref Ctxt Defs} ->
 newLHS fc envlen allvars var con tm
     = do let (f, args) = getFnArgs tm []
          let keep = map (const (Explicit fc (Implicit fc True)))
-                        (take envlen args)
+                        (mapMaybe isExplicit $ take envlen args)
          let ups = drop envlen args
          ups' <- traverse (update allvars var con) ups
          pure $ apply f (keep ++ ups')

tests/Main.idr

@@ -132,7 +132,7 @@ idrisTests = MkTestPool "Misc" [] Nothing
        -- Namespace blocks
        "namespace001", "namespace002", "namespace003", "namespace004", "namespace005",
        -- Parameters blocks
-       "params001", "params002", "params003",
+       "params001", "params002", "params003", "params004",
        -- Larger programs arising from real usage. Typically things with
        -- interesting interactions between features
        "real001", "real002",

tests/idris2/misc/params004/Issue2331.idr

@@ -0,0 +1,5 @@
+parameters {auto _ : ()}
+
+  f : Nat -> Nat
+  f m = ?a
+

tests/idris2/misc/params004/expected

@@ -0,0 +1,4 @@
+1/1: Building Issue2331 (Issue2331.idr)
+Main>   f 0 = ?a_0
+  f (S k) = ?a_1
+Main> Bye for now!

tests/idris2/misc/params004/input

@@ -0,0 +1,2 @@
+:cs 4 5 m
+:q

tests/idris2/misc/params004/run

@@ -0,0 +1,3 @@
+. ../../../testutils.sh
+
+idris2 Issue2331.idr < input