SERVER-41750 refactor renamed paths API.

1 files changed, 102 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/semantic_analysis.h b/src/mongo/db/pipeline/semantic_analysis.h
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+++ b/src/mongo/db/pipeline/semantic_analysis.h
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+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <boost/optional.hpp>
+#include <set>
+#include <string>
+
+#include "mongo/db/pipeline/document_source.h"
+#include "mongo/db/pipeline/pipeline.h"
+
+namespace mongo::semantic_analysis {
+
+enum class Direction { kForward, kBackward };
+
+/**
+ * Takes in a set of paths the caller is interested in, a pipeline stage, and a direction.  If the
+ * direction is "forward", the paths given must exist before the stage is executed in the pipeline.
+ * If the direction is "backward," the paths must exist after the stage is executed in the pipeline.
+ * Returns boost::none if any of the pathsOfInterest are modified by the current stage. If all of
+ * the pathsOfInterest are preserved (but possibly renamed), we return a mapping from
+ * [pathOfInterest] --> [newName], where "newName" is the name of "pathOfInterest" on the "other
+ * side" of the stage with respect to the given direction.
+ *
+ * For example, say pathsOfInterest contains "a", a path name that exists before nextStage is run in
+ * the pipeline, and direction is forward. Say nextStage preserves all the paths but renames "a" to
+ * "b"; we would return a mapping a-->b.
+ *
+ * Conversely, say pathsOfInterest contains "b", a path name that exists after nextStage is run in
+ * the pipeline, and direction is backward. Say nextStage preserves all the paths but renamed "a" to
+ * "b"; we would return a mapping b-->a.
+ */
+boost::optional<StringMap<std::string>> renamedPaths(const std::set<std::string>& pathsOfInterest,
+                                                     const DocumentSource& stage,
+                                                     const Direction& traversalDir);
+/**
+ * Tracks renames by walking a pipeline forwards. Takes two forward iterators that represent two
+ * stages in an aggregation pipeline, with 'start' coming before 'end,' as well as a set of path
+ * names the caller is interested in. Returns boost::none if any of these paths are modified by the
+ * pipeline from stages ['start' - 'end'); otherwise returns a mapping for each path in
+ * 'pathsOfInterest' from its name before stage 'start' to its name before stage 'end'. To track
+ * renames through an entire pipeline, 'start' should refer to the first stage in the pipeline while
+ * 'end' should be an iterator referring to the past-the-end stage.
+ */
+boost::optional<StringMap<std::string>> renamedPaths(
+    const Pipeline::SourceContainer::const_iterator start,
+    const Pipeline::SourceContainer::const_iterator end,
+    const std::set<std::string>& pathsOfInterest);
+
+/**
+ * Tracks renames by walking a pipeline backwards. Takes two reverse iterators that represent two
+ * stages in an aggregation pipeline, with 'start' coming after 'end,' as well as a set of path
+ * names the caller is interested in. Returns boost::none if any of these paths were modified by the
+ * pipeline from stages ('end' - 'start']; otherwise returns a mapping for each path in
+ * 'pathsOfInterest' from its name after stage 'start' to its name as it was after stage 'end'. To
+ * track renames through an entire pipeline, 'start' should refer to the last stage in the pipeline
+ * while 'end' should refer to the (hypothetical) stage preceeding the first stage in the pipeline
+ * (the 'reverse end').
+ */
+boost::optional<StringMap<std::string>> renamedPaths(
+    const Pipeline::SourceContainer::const_reverse_iterator start,
+    const Pipeline::SourceContainer::const_reverse_iterator end,
+    const std::set<std::string>& pathsOfInterest);
+
+/**
+ * Given a set of paths 'dependencies', determines which of those paths will be modified if all
+ * paths except those in 'preservedPaths' are modified.
+ *
+ * For example, extractModifiedDependencies({'a', 'b', 'c.d', 'e'}, {'a', 'b.c', c'}) returns
+ * {'b', 'e'}, since 'b' and 'e' are not preserved (only 'b.c' is preserved).
+ */
+std::set<std::string> extractModifiedDependencies(const std::set<std::string>& dependencies,
+                                                  const std::set<std::string>& preservedPaths);
+
+}  // namespace mongo::semantic_analysis