chore: [match_pattern] should enforce [expose] (#9534)

src/Init/Data/List/ToArrayImpl.lean

@@ -31,6 +31,6 @@ both `List.toArray` and `Array.mk`.
 -/
 -- This function is exported to C, where it is called by `Array.mk`
 -- (the constructor) to implement this functionality.
-@[inline, match_pattern, pp_nodot, export lean_list_to_array]
+@[inline, expose, match_pattern, pp_nodot, export lean_list_to_array]
 def List.toArrayImpl (xs : List α) : Array α :=
   xs.toArrayAux (Array.mkEmpty xs.length)

src/Lean/Elab/Tactic/Do/ProofMode/MGoal.lean

@@ -19,8 +19,8 @@ namespace Lean.Elab.Tactic.Do.ProofMode
 open Lean Elab Meta
 open Std.Do Std.Tactic.Do
 
-@[match_pattern] def nameAnnotation := `name
-@[match_pattern] def uniqAnnotation := `uniq
+@[match_pattern] private def nameAnnotation := `name
+@[match_pattern] private def uniqAnnotation := `uniq
 
 structure Hyp where
   name : Name

src/Lean/Meta/Match/MatchPatternAttr.lean

@@ -33,6 +33,10 @@ def isYellow (color : String) : Bool :=
 @[builtin_doc]
 builtin_initialize matchPatternAttr : TagAttribute ←
   registerTagAttribute `match_pattern "mark that a definition can be used in a pattern (remark: the dependent pattern matching compiler will unfold the definition)"
+    (validate := fun declName => do
+      withExporting (isExporting := !isPrivateName declName) do
+        if !(← getConstInfo declName).isDefinition then
+          throwError "invalid `@[match_pattern]` attribute, '{declName}' is not an exposed definition")
 
 @[export lean_has_match_pattern_attribute]
 def hasMatchPatternAttribute (env : Environment) (n : Name) : Bool :=