SERVER-25535 Remove injectExpressionContext().

These methods were formally used to propagate a new ExpressionContext to
stages, accumulators, or expressions which potentially needed to
comparisons. Originally, this was necessary since Pipeline parsing
happened outside of the collection lock and thus could not determine if
there was a default collation on the collection. This meant that the
collation could change after parsing and any operators that might
compare strings would need to know about it.

We have since moved parsing within the lock, so the collation can be
known at parse time and the ExpressionContext should not change. This
patch requires an ExpressionContext at construction time, and disallows
changing the collation on an ExpressionContext.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/document_source_replace_root.h b/src/mongo/db/pipeline/document_source_replace_root.h
index f3313ec5f7a..4656a6cdc2d 100644
--- a/src/mongo/db/pipeline/document_source_replace_root.h
+++ b/src/mongo/db/pipeline/document_source_replace_root.h
@@ -48,6 +48,8 @@ public:
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
 private:
+    // It is illegal to construct a DocumentSourceReplaceRoot directly, use createFromBson()
+    // instead.
     DocumentSourceReplaceRoot() = default;
 };