CollectMVars.lean

/-
Copyright (c) 2020 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Leonardo de Moura
-/
import Lean.Util.CollectMVars
import Lean.Meta.Basic

namespace Lean.Meta

/--
  Collect unassigned metavariables occurring in the given expression.

  Remark: if `e` contains `?m` and there is a `t` assigned to `?m`, we
  collect unassigned metavariables occurring in `t`.

  Remark: if `e` contains `?m` and `?m` is delayed assigned to some term `t`,
  we collect `?m` and unassigned metavariables occurring in `t`.
  We collect `?m` because it has not been assigned yet. -/
partial def collectMVars (e : Expr) : StateRefT CollectMVars.State MetaM Unit := do
  let e ← instantiateMVars e
  let s ← get
  let resultSavedSize := s.result.size
  let s := e.collectMVars s
  set s
  for mvarId in s.result[resultSavedSize:] do
    match (← getDelayedMVarAssignment? mvarId) with
    | none   => pure ()
    | some d => collectMVars (mkMVar d.mvarIdPending)

/-- Return metavariables occurring in the given expression. See `collectMVars` -/
def getMVars (e : Expr) : MetaM (Array MVarId) := do
  let (_, s) ← (collectMVars e).run {}
  pure s.result

/-- Similar to `getMVars`, but removes delayed assignments. -/
def getMVarsNoDelayed (e : Expr) : MetaM (Array MVarId) := do
  let mvarIds ← getMVars e
  mvarIds.filterM fun mvarId => not <$> mvarId.isDelayedAssigned

def collectMVarsAtDecl (d : Declaration) : StateRefT CollectMVars.State MetaM Unit :=
  d.forExprM collectMVars

def getMVarsAtDecl (d : Declaration) : MetaM (Array MVarId) := do
  let (_, s) ← (collectMVarsAtDecl d).run {}
  pure s.result

end Lean.Meta