chore: add deprecated function

Misleading name and docstring. The function can be applied to types
that are not propositions.

src/Lean/Meta/Tactic/Simp/Main.lean

@@ -865,28 +865,34 @@ def simpTarget (mvarId : MVarId) (ctx : Simp.Context) (simprocs : SimprocsArray
     simpTargetCore mvarId ctx simprocs discharge? mayCloseGoal stats
 
 /--
-  Apply the result `r` for `prop` (which is inhabited by `proof`). Return `none` if the goal was closed. Return `some (proof', prop')`
-  otherwise, where `proof' : prop'` and `prop'` is the simplified `prop`.
+Applies the result `r` for `type` (which is inhabited by `val`). Returns `none` if the goal was closed. Returns `some (val', type')`
+otherwise, where `val' : type'` and `type'` is the simplified `type`.
 
-  This method assumes `mvarId` is not assigned, and we are already using `mvarId`s local context. -/
-def applySimpResultToProp (mvarId : MVarId) (proof : Expr) (prop : Expr) (r : Simp.Result) (mayCloseGoal := true) : MetaM (Option (Expr × Expr)) := do
+This method assumes `mvarId` is not assigned, and we are already using `mvarId`s local context. -/
+def applySimpResult (mvarId : MVarId) (val : Expr) (type : Expr) (r : Simp.Result) (mayCloseGoal := true) : MetaM (Option (Expr × Expr)) := do
   if mayCloseGoal && r.expr.isFalse then
     match r.proof? with
-    | some eqProof => mvarId.assign (← mkFalseElim (← mvarId.getType) (← mkEqMP eqProof proof))
-    | none => mvarId.assign (← mkFalseElim (← mvarId.getType) proof)
+    | some eqProof => mvarId.assign (← mkFalseElim (← mvarId.getType) (mkApp4 (mkConst ``Eq.mp [levelZero]) type r.expr eqProof val))
+    | none => mvarId.assign (← mkFalseElim (← mvarId.getType) val)
     return none
   else
     match r.proof? with
-    | some eqProof => return some ((← mkEqMP eqProof proof), r.expr)
+    | some eqProof =>
+      let u ← getLevel type
+      return some (mkApp4 (mkConst ``Eq.mp [u]) type r.expr eqProof val, r.expr)
     | none =>
-      if r.expr != prop then
-        return some ((← mkExpectedTypeHint proof r.expr), r.expr)
+      if r.expr != type then
+        return some ((← mkExpectedTypeHint val r.expr), r.expr)
       else
-        return some (proof, r.expr)
+        return some (val, r.expr)
+
+@[deprecated applySimpResult (since := "2025-03-26")]
+def applySimpResultToProp (mvarId : MVarId) (proof : Expr) (prop : Expr) (r : Simp.Result) (mayCloseGoal := true) : MetaM (Option (Expr × Expr)) :=
+  applySimpResult mvarId proof prop r mayCloseGoal
 
 def applySimpResultToFVarId (mvarId : MVarId) (fvarId : FVarId) (r : Simp.Result) (mayCloseGoal : Bool) : MetaM (Option (Expr × Expr)) := do
   let localDecl ← fvarId.getDecl
-  applySimpResultToProp mvarId (mkFVar fvarId) localDecl.type r mayCloseGoal
+  applySimpResult mvarId (mkFVar fvarId) localDecl.type r mayCloseGoal
 
 /--
   Simplify `prop` (which is inhabited by `proof`). Return `none` if the goal was closed. Return `some (proof', prop')`
@@ -896,7 +902,7 @@ def applySimpResultToFVarId (mvarId : MVarId) (fvarId : FVarId) (r : Simp.Result
 def simpStep (mvarId : MVarId) (proof : Expr) (prop : Expr) (ctx : Simp.Context) (simprocs : SimprocsArray := #[]) (discharge? : Option Simp.Discharge := none)
     (mayCloseGoal := true) (stats : Stats := {}) : MetaM (Option (Expr × Expr) × Stats) := do
   let (r, stats) ← simp prop ctx simprocs discharge? stats
-  return (← applySimpResultToProp mvarId proof prop r (mayCloseGoal := mayCloseGoal), stats)
+  return (← applySimpResult mvarId proof prop r (mayCloseGoal := mayCloseGoal), stats)
 
 def applySimpResultToLocalDeclCore (mvarId : MVarId) (fvarId : FVarId) (r : Option (Expr × Expr)) : MetaM (Option (FVarId × MVarId)) := do
   match r with
@@ -950,7 +956,7 @@ def simpGoal (mvarId : MVarId) (ctx : Simp.Context) (simprocs : SimprocsArray :=
       let (r, stats') ← simp type ctx simprocs discharge? stats
       stats := stats'
       match r.proof? with
-      | some _ => match (← applySimpResultToProp mvarIdNew (mkFVar fvarId) type r) with
+      | some _ => match (← applySimpResult mvarIdNew (mkFVar fvarId) type r) with
         | none => return (none, stats)
         | some (value, type) => toAssert := toAssert.push { userName := localDecl.userName, type := type, value := value }
       | none =>

src/Lean/Meta/Tactic/Simp/Rewrite.lean

@@ -625,7 +625,7 @@ def dischargeDefault? (e : Expr) : SimpM (Option Expr) := do
     if let some r ← dischargeEqnThmHypothesis? e then return some r
   let r ← simp e
   if let some p ← dischargeRfl r.expr then
-    return some (← mkEqMPR (← r.getProof) p)
+    return some (mkApp4 (mkConst ``Eq.mpr [levelZero]) e r.expr (← r.getProof) p)
   else if r.expr.isTrue then
     return some (← mkOfEqTrue (← r.getProof))
   else