From 712013ffd49d76c699a5a0128f5605a10b497967 Mon Sep 17 00:00:00 2001
From: David Storch <david.storch@mongodb.com>
Date: Wed, 9 Sep 2020 18:27:22 -0400
Subject: SERVER-50884 Change order of SBE traverse 'from' and 'in' branches in
 debug output

---
 src/mongo/db/exec/sbe/parser/parser.cpp   | 14 +++++++-------
 src/mongo/db/exec/sbe/stages/traverse.cpp |  8 ++++----
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/mongo/db/exec/sbe/parser/parser.cpp b/src/mongo/db/exec/sbe/parser/parser.cpp
index acbb6b983fd..3d61b5966e2 100644
--- a/src/mongo/db/exec/sbe/parser/parser.cpp
+++ b/src/mongo/db/exec/sbe/parser/parser.cpp
@@ -130,8 +130,8 @@ static constexpr auto kSyntax = R"(
                                        IDENT # input of traverse
                                        ('{' EXPR '}')? # optional fold expression
                                        ('{' EXPR '}')? # optional final expression
-                                       'in' OPERATOR
                                        'from' OPERATOR
+                                       'in' OPERATOR
                 EXCHANGE <- 'exchange' IDENT_LIST NUMBER IDENT OPERATOR
                 SORT <- 'sort' IDENT_LIST IDENT_LIST OPERATOR
                 UNWIND <- 'unwind' IDENT IDENT IDENT UNWIND_FLAG OPERATOR
@@ -926,17 +926,17 @@ void Parser::walkTraverse(AstQuery& ast) {
     size_t finalPos = 0;
 
     if (ast.nodes.size() == 5) {
-        inPos = 3;
-        fromPos = 4;
+        fromPos = 3;
+        inPos = 4;
     } else if (ast.nodes.size() == 6) {
         foldPos = 3;
-        inPos = 4;
-        fromPos = 5;
+        fromPos = 4;
+        inPos = 5;
     } else {
         foldPos = 3;
         finalPos = 4;
-        inPos = 5;
-        fromPos = 6;
+        fromPos = 5;
+        inPos = 6;
     }
     ast.stage = makeS<TraverseStage>(std::move(ast.nodes[fromPos]->stage),
                                      std::move(ast.nodes[inPos]->stage),
diff --git a/src/mongo/db/exec/sbe/stages/traverse.cpp b/src/mongo/db/exec/sbe/stages/traverse.cpp
index d1438883141..a764c4c6698 100644
--- a/src/mongo/db/exec/sbe/stages/traverse.cpp
+++ b/src/mongo/db/exec/sbe/stages/traverse.cpp
@@ -300,14 +300,14 @@ std::vector<DebugPrinter::Block> TraverseStage::debugPrint() const {
     }
 
     DebugPrinter::addNewLine(ret);
-    DebugPrinter::addIdentifier(ret, "in");
+    DebugPrinter::addIdentifier(ret, "from");
     ret.emplace_back(DebugPrinter::Block::cmdIncIndent);
-    DebugPrinter::addBlocks(ret, _children[1]->debugPrint());
+    DebugPrinter::addBlocks(ret, _children[0]->debugPrint());
     ret.emplace_back(DebugPrinter::Block::cmdDecIndent);
 
-    DebugPrinter::addIdentifier(ret, "from");
+    DebugPrinter::addIdentifier(ret, "in");
     ret.emplace_back(DebugPrinter::Block::cmdIncIndent);
-    DebugPrinter::addBlocks(ret, _children[0]->debugPrint());
+    DebugPrinter::addBlocks(ret, _children[1]->debugPrint());
     ret.emplace_back(DebugPrinter::Block::cmdDecIndent);
 
     return ret;
-- 
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