From 265c4da7b3a9b97d40054e9d4da8ad75c4aca8a0 Mon Sep 17 00:00:00 2001
From: James Wahlin <james@mongodb.com>
Date: Fri, 1 May 2020 13:54:53 -0400
Subject: SERVER-47765 Make variables declared above DocumentSourceGraphLookup
 available within

---
 jstests/aggregation/sources/graphLookup/filter.js  | 24 ++++++++++++++++++++++
 .../db/pipeline/document_source_graph_lookup.cpp   |  4 ++++
 2 files changed, 28 insertions(+)

diff --git a/jstests/aggregation/sources/graphLookup/filter.js b/jstests/aggregation/sources/graphLookup/filter.js
index 69027500aae..ce1af67bd08 100644
--- a/jstests/aggregation/sources/graphLookup/filter.js
+++ b/jstests/aggregation/sources/graphLookup/filter.js
@@ -91,4 +91,28 @@
               .toArray()[0];
 
     assert.eq(res.results.length, 1);
+
+    // $expr within `restrictSearchWithMatch` has access to variables declared at a higher level.
+    res = local
+              .aggregate([{
+                  $lookup: {
+                      from: "local",
+                      let : {foo: true},
+                      pipeline: [{
+                          $graphLookup: {
+                              from: "foreign",
+                              startWith: "$starting",
+                              connectFromField: "to",
+                              connectToField: "from",
+                              as: "results",
+                              restrictSearchWithMatch:
+                                  {$expr: {$eq: ["$shouldBeIncluded", "$$foo"]}}
+                          }
+                      }],
+                      as: "array"
+                  }
+              }])
+              .toArray()[0];
+
+    assert.eq(res.array[0].results.length, 1);
 })();
diff --git a/src/mongo/db/pipeline/document_source_graph_lookup.cpp b/src/mongo/db/pipeline/document_source_graph_lookup.cpp
index 6e9c4776df4..bc055a679e3 100644
--- a/src/mongo/db/pipeline/document_source_graph_lookup.cpp
+++ b/src/mongo/db/pipeline/document_source_graph_lookup.cpp
@@ -482,6 +482,10 @@ DocumentSourceGraphLookUp::DocumentSourceGraphLookUp(
                          boost::none,
                          expCtx->getCollator() ? expCtx->getCollator()->clone() : nullptr);
 
+    _fromExpCtx->variables = expCtx->variables;
+    _fromExpCtx->variablesParseState =
+        expCtx->variablesParseState.copyWith(expCtx->variables.useIdGenerator());
+
     // We append an additional BSONObj to '_fromPipeline' as a placeholder for the $match stage
     // we'll eventually construct from the input document.
     _fromPipeline = resolvedNamespace.pipeline;
-- 
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