From 2e3587872c3d2a5a88b8b8d9331c0d72a10e240a Mon Sep 17 00:00:00 2001
From: Leonardo de Moura <leonardo@microsoft.com>
Date: Wed, 12 Aug 2020 16:18:22 -0700
Subject: [PATCH] feat: add `withSynthesize`

---
 src/Lean/Elab/Match.lean          |  9 +++++----
 src/Lean/Elab/SyntheticMVars.lean | 13 +++++++++----
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/src/Lean/Elab/Match.lean b/src/Lean/Elab/Match.lean
index 1b4f2b192e..f4145f3ab3 100644
--- a/src/Lean/Elab/Match.lean
+++ b/src/Lean/Elab/Match.lean
@@ -3,9 +3,9 @@ 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.Elab.Term
 import Lean.Meta.EqnCompiler.MatchPattern
 import Lean.Meta.EqnCompiler.DepElim
+import Lean.Elab.SyntheticMVars
 
 namespace Lean
 namespace Elab
@@ -365,8 +365,9 @@ private partial def elabPatternsAux (ref : Syntax) (patternStxs : Array Syntax)
   else
     pure patterns
 
-private def elabPatterns (ref : Syntax) (patternStxs : Array Syntax) (matchType : Expr) : TermElabM (Array Expr) := do
-patterns ← elabPatternsAux ref patternStxs 0 matchType #[];
+private def elabPatterns (ref : Syntax) (patternVars : Array Expr) (patternStxs : Array Syntax) (matchType : Expr) : TermElabM (Array Expr) := do
+patterns ← withSynthesize $ elabPatternsAux ref patternStxs 0 matchType #[];
+patterns ← patterns.mapM $ instantiateMVars ref;
 trace `Elab.match ref fun _ => "patterns: " ++ patterns;
 pure patterns
 
@@ -375,7 +376,7 @@ def elabMatchAltView (alt : MatchAltView) (matchType : Expr) : TermElabM (Meta.D
 trace `Elab.match alt.ref fun _ => "patternVars: " ++ toString patternVars;
 withPatternVars alt.ref patternVars fun xs => do
   trace `Elab.match alt.ref fun _ => "xs: " ++ xs;
-  ps ← elabPatterns alt.ref alt.patterns matchType;
+  ps ← elabPatterns alt.ref xs alt.patterns matchType;
   -- TODO
   pure (⟨[], []⟩, arbitrary _)
 
diff --git a/src/Lean/Elab/SyntheticMVars.lean b/src/Lean/Elab/SyntheticMVars.lean
index ce1e427066..71d20ba3c4 100644
--- a/src/Lean/Elab/SyntheticMVars.lean
+++ b/src/Lean/Elab/SyntheticMVars.lean
@@ -210,18 +210,23 @@ private partial def synthesizeSyntheticMVarsAux (mayPostpone := true) : Unit →
 def synthesizeSyntheticMVars (mayPostpone := true) : TermElabM Unit :=
 synthesizeSyntheticMVarsAux mayPostpone ()
 
-/-- Elaborate `stx`, and make sure all pending synthetic metavariables created while elaborating `stx` are solved. -/
-def elabTermAndSynthesize (stx : Syntax) (expectedType? : Option Expr) : TermElabM Expr := do
+/-- Execute `k`, and make sure all pending synthetic metavariables created while executing `k` are solved. -/
+def withSynthesize {α} (k : TermElabM α) : TermElabM α := do
 s ← get;
 let syntheticMVars := s.syntheticMVars;
 modify $ fun s => { s with syntheticMVars := [] };
 finally
   (do
-     v ← elabTerm stx expectedType?;
+     a ← k;
      synthesizeSyntheticMVars false;
-     instantiateMVars stx v)
+     pure a)
   (modify $ fun s => { s with syntheticMVars := s.syntheticMVars ++ syntheticMVars })
 
+/-- Elaborate `stx`, and make sure all pending synthetic metavariables created while elaborating `stx` are solved. -/
+def elabTermAndSynthesize (stx : Syntax) (expectedType? : Option Expr) : TermElabM Expr := do
+v ← withSynthesize $ elabTerm stx expectedType?;
+instantiateMVars stx v
+
 end Term
 end Elab
 end Lean