fix: condition for selecting split target

Only discriminants must not have loose bound variables

src/Lean/Meta/Match/MatcherInfo.lean

@@ -29,8 +29,12 @@ def MatcherInfo.numAlts (info : MatcherInfo) : Nat :=
 def MatcherInfo.arity (info : MatcherInfo) : Nat :=
   info.numParams + 1 + info.numDiscrs + info.numAlts
 
+def MatcherInfo.getFirstDiscrPos (info : MatcherInfo) : Nat :=
+  info.numParams + 1
+
 def MatcherInfo.getMotivePos (info : MatcherInfo) : Nat :=
   info.numParams
+
 namespace Extension
 
 structure Entry where
@@ -79,15 +83,18 @@ def isMatcherCore (env : Environment) (declName : Name) : Bool :=
 def isMatcher [Monad m] [MonadEnv m] (declName : Name) : m Bool :=
   return isMatcherCore (← getEnv) declName
 
-def isMatcherAppCore (env : Environment) (e : Expr) : Bool :=
+def isMatcherAppCore? (env : Environment) (e : Expr) : Option MatcherInfo :=
   let fn := e.getAppFn
   if fn.isConst then
     if let some matcherInfo := getMatcherInfoCore? env fn.constName! then
-      e.getAppNumArgs ≥ matcherInfo.arity
+      if e.getAppNumArgs ≥ matcherInfo.arity then some matcherInfo else none
     else
-      false
+      none
   else
-    false
+    none
+
+def isMatcherAppCore (env : Environment) (e : Expr) : Bool :=
+  isMatcherAppCore? env e |>.isSome
 
 def isMatcherApp [Monad m] [MonadEnv m] (e : Expr) : m Bool :=
   return isMatcherAppCore (← getEnv) e

src/Lean/Meta/Tactic/Split.lean

@@ -100,7 +100,7 @@ def splitMatch (mvarId : MVarId) (e : Expr) : MetaM (List MVarId) := do
 
 /-- Return an `if-then-else` or `match-expr` to split. -/
 partial def findSplit? (env : Environment) (e : Expr) : Option Expr :=
-  if let some target := e.find? fun e => !e.hasLooseBVars && (e.isIte || e.isDIte || isMatcherAppCore env e) then
+  if let some target := e.find? isCandidate then
     if e.isIte || e.isDIte then
       let cond := target.getArg! 1 5
       -- Try to find a nested `if` in `cond`
@@ -109,6 +109,18 @@ partial def findSplit? (env : Environment) (e : Expr) : Option Expr :=
       some target
   else
     none
+where
+  isCandidate (e : Expr) : Bool := do
+    if e.isIte || e.isDIte then
+      !(e.getArg! 1 5).hasLooseBVars
+    else if let some info := isMatcherAppCore? env e then
+      let args := e.getAppArgs
+      for i in [info.getFirstDiscrPos : info.getFirstDiscrPos + info.numDiscrs] do
+        if args[i].hasLooseBVars then
+          return false
+      return true
+    else
+      false
 
 end Split
 
@@ -121,6 +133,7 @@ def splitTarget? (mvarId : MVarId) : MetaM (Option (List MVarId)) := commitWhenS
     else
       splitMatch mvarId e
   else
+    trace[Meta.Tactic.split] "did not find term to split\n{MessageData.ofGoal mvarId}"
     return none
 
 def splitLocalDecl? (mvarId : MVarId) (fvarId : FVarId) : MetaM (Option (List MVarId)) := commitWhenSome? do
@@ -137,4 +150,6 @@ def splitLocalDecl? (mvarId : MVarId) (fvarId : FVarId) : MetaM (Option (List MV
     else
       return none
 
+builtin_initialize registerTraceClass `Meta.Tactic.split
+
 end Lean.Meta

src/Lean/Meta/Tactic/SplitIf.lean

@@ -63,7 +63,7 @@ def discharge? (useDecide := false) : Simp.Discharge := fun prop => do
 
 /-- Return the condition of an `if` expression to case split. -/
 partial def findIfToSplit? (e : Expr) : Option Expr :=
-  if let some iteApp := e.find? fun e => !e.hasLooseBVars && (e.isIte || e.isDIte) then
+  if let some iteApp := e.find? fun e => (e.isIte || e.isDIte) && !(e.getArg! 1 5).hasLooseBVars then
     let cond := iteApp.getArg! 1 5
     -- Try to find a nested `if` in `cond`
     findIfToSplit? cond |>.getD cond