feat: Add QuotedLevelDefEq to match QuotedDefEq

Qq/MetaM.lean

@@ -85,3 +85,26 @@ def assertDefEqQ {α : Q(Sort $u)} (a b : Q($α)) : MetaM (PLift (QuotedDefEq a
   match ← isDefEqQ a b with
   | .defEq witness => return ⟨witness⟩
   | .notDefEq => throwError "{a} is not definitionally equal to{indentExpr b}"
+
+/-- The result of `Qq.isLevelDefEqQ`; `MaybeLevelDefEq u v` is an optional version of `$u =QL $v`. -/
+inductive MaybeLevelDefEq (u v : Level) where
+  | defEq : QuotedLevelDefEq u v → MaybeLevelDefEq u v
+  | notDefEq : MaybeLevelDefEq u v
+
+instance : Repr (MaybeLevelDefEq u v) where
+  reprPrec := fun
+    | .defEq _, prec => Repr.addAppParen "defEq _" prec
+    | .notDefEq, _ => "notDefEq"
+
+/-- A version of `Lean.Meta.isLevelDefEq` which returns a strongly-typed witness rather than a bool. -/
+def isLevelDefEqQ (u v : Level) : MetaM (MaybeLevelDefEq u v) := do
+  if ← isLevelDefEq u v then
+    return .defEq ⟨⟩
+  else
+    return .notDefEq
+
+/-- Like `Qq.isLevelDefEqQ`, but throws an error if not defeq. -/
+def assertLevelDefEqQ (u v : Level) : MetaM (PLift (QuotedLevelDefEq u v)) := do
+  match ← isLevelDefEqQ u v with
+  | .defEq witness => return ⟨witness⟩
+  | .notDefEq => throwError "{u} and {v} are not definitionally equal"

Qq/Typ.lean

@@ -38,6 +38,7 @@ protected abbrev Quoted.ty (t : Quoted α) : Expr := α
 You should usually write this using the notation `$lhs =Q $rhs`.
 -/
 structure QuotedDefEq {α : Quoted (.sort u)} (lhs rhs : Quoted α) : Prop where
+  /-- For a safer constructor, see `Qq.assertDefEqQ`. -/
   unsafeIntro ::
 
 /--
@@ -46,6 +47,7 @@ structure QuotedDefEq {α : Quoted (.sort u)} (lhs rhs : Quoted α) : Prop where
 You should usually write this using the notation `$u =QL $v`.
 -/
 structure QuotedLevelDefEq (u v : Level) : Prop where
+  /-- For a safer constructor, see `Qq.assertLevelDefEqQ`. -/
   unsafeIntro ::
 
 open Meta in