feat: check given constructor resulting type

src/Lean/Elab/Inductive.lean

@@ -203,7 +203,11 @@ r.view.ctors.toList.mapM fun ctorView => Term.elabBinders ctorView.binders.getAr
       pure indFVar
     | some ctorType => do {
       type ← Term.elabTerm ctorType none;
-      -- TODO: check whether resulting type is indFVar
+      resultingType ← getResultingType ref type;
+      unless (resultingType.getAppFn == indFVar) $
+        Term.throwError ref ("unexpected constructor resulting type" ++ indentExpr resultingType);
+      unlessM (Term.isType ref resultingType) $
+        Term.throwError ref ("unexpected constructor resulting type, type expected" ++ indentExpr resultingType);
       pure type
     };
   type ← Term.mkForall ref ctorParams type;

tests/lean/inductive1.lean

@@ -98,3 +98,11 @@ end
 inductive T1 : Nat → Type
 | z1 : T1 0
 | z2 -- constructor resulting type must be specified in inductive family declaration
+
+
+-- Test12
+inductive T1 : Nat → Type
+| z1 : T1 -- unexpected constructor resulting type
+
+inductive T1 : Nat → Type
+| z1 : Nat -- unexpected constructor resulting type

tests/lean/inductive1.lean.expected.out

@@ -22,3 +22,7 @@ inductive1.lean:82:10: error: invalid use of attributes in inductive declaration
 inductive1.lean:85:0: error: invalid 'private' constructor in a 'private' inductive datatype
 inductive1.lean:93:7: error: invalid inductive type, cannot mix unsafe and safe declarations in a mutually inductive datatypes
 inductive1.lean:100:0: error: constructor resulting type must be specified in inductive family declaration
+inductive1.lean:105:0: error: unexpected constructor resulting type, type expected
+  T1
+inductive1.lean:108:0: error: unexpected constructor resulting type
+  Nat