SERVER-66548 Add support for dependency tracking to $redact

(cherry picked from commit cc4968771221658d66ff42ed2fb861656c5683ca)

2 files changed, 31 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/document_source_redact.h b/src/mongo/db/pipeline/document_source_redact.h
index 10fcfc14f63..b566f2c7adf 100644
--- a/src/mongo/db/pipeline/document_source_redact.h
+++ b/src/mongo/db/pipeline/document_source_redact.h
@@ -72,6 +72,16 @@ public:
         return _expression;
     }
 
+    DepsTracker::State getDependencies(DepsTracker* deps) const final {
+        // Add the dependencies of the expression but all we really care about is variable
+        // references for correlation analysis. The field references may get populated but we'll
+        // still require the full document since the $redact may descend arbitrary levels of nested
+        // documents that is only known at runtime.
+        _expression->addDependencies(deps);
+        deps->needWholeDocument = true;
+        return DepsTracker::State::SEE_NEXT;
+    }
+
 private:
     DocumentSourceRedact(const boost::intrusive_ptr<ExpressionContext>& expCtx,
                          const boost::intrusive_ptr<Expression>& previsit);
diff --git a/src/mongo/db/pipeline/document_source_redact_test.cpp b/src/mongo/db/pipeline/document_source_redact_test.cpp
index 95d001e4dac..6605796138b 100644
--- a/src/mongo/db/pipeline/document_source_redact_test.cpp
+++ b/src/mongo/db/pipeline/document_source_redact_test.cpp
@@ -81,5 +81,26 @@ TEST_F(DocumentSourceRedactTest, ShouldPropagatePauses) {
     ASSERT_TRUE(redact->getNext().isEOF());
     ASSERT_TRUE(redact->getNext().isEOF());
 }
+
+TEST_F(DocumentSourceRedactTest, ReportsVariableDependencies) {
+    auto varId = getExpCtx()->variablesParseState.defineVariable("var");
+    auto redactSpec = fromjson(R"({
+        "$redact" : {
+            "$cond" : {
+                "if" : "$$var",
+                "then" : "$$PRUNE",
+                "else" : "$$DESCEND"
+            }
+        }
+    })");
+    auto redact = DocumentSourceRedact::createFromBson(redactSpec.firstElement(), getExpCtx());
+
+    DepsTracker deps;
+    ASSERT_EQ(redact->getDependencies(&deps), DepsTracker::State::SEE_NEXT);
+    ASSERT_EQ(deps.needWholeDocument, true);
+    ASSERT_TRUE(deps.fields.empty());
+    ASSERT_EQ(deps.vars.count(varId), 1);
+}
+
 }  // namespace
 }  // namespace mongo