fix: check type mismatch at dependent pattern matching compiler

see issue #1057

src/Lean/Meta/Match/Match.lean

@@ -51,7 +51,13 @@ where
         loop lhss alts minors
 
 def assignGoalOf (p : Problem) (e : Expr) : MetaM Unit :=
-  withGoalOf p (assignExprMVar p.mvarId e)
+  withGoalOf p do
+    let mvar := mkMVar p.mvarId
+    let mvarType ← inferType mvar
+    let eType ← inferType e
+    unless (← isDefEq mvarType eType) do
+      throwError "dependent elimination failed, type mismatch when solving alternative with type{indentExpr eType}\nbut expected{indentExpr mvarType}"
+    assignExprMVar p.mvarId e
 
 structure State where
   used            : Std.HashSet Nat := {} -- used alternatives

tests/lean/1057.lean

@@ -0,0 +1,9 @@
+inductive T
+  | t : T
+
+@[reducible] def T.eval : T → Type
+  | T.t => Int
+
+def T.default (τ : T) : τ.eval :=
+  match τ, τ.eval with
+  | T.t, .(Int) => (0 : Int)

tests/lean/1057.lean.expected.out

@@ -0,0 +1,4 @@
+1057.lean:8:2-9:28: error: dependent elimination failed, type mismatch when solving alternative with type
+  motive t Int
+but expected
+  motive t x✝