GODRIVER-3523 Drop support for MongoDB 4.0.

[qingyang-hu]

GODRIVER-3523

Summary

Drop support for MongoDB 4.0.

Background & Motivation

[mongodb-drivers-pr-bot]

🧪 Performance Results

Commit SHA: 0ce103e

The following benchmark tests for version 68e6e20231536c0007d047c8 had statistically significant changes (i.e., |z-score| > 1.96):

Benchmark	Measurement	% Change	Patch Value	Stable Region	H-Score	Z-Score
BenchmarkBSONDeepDocumentDecoding	ops_per_second_min	22.4338	2431.1203	Avg: 1985.6613 Med: 1996.0917 Stdev: 167.1050	0.8135	2.6657
BenchmarkBSONFullDocumentDecoding	total_bytes_allocated	16.6299	415701824.0000	Avg: 356428068.9091 Med: 360143680.0000 Stdev: 20551053.1642	0.8523	2.8842
BenchmarkBSONFlatDocumentEncoding	total_mem_allocs	14.6900	265352.0000	Avg: 231364.4690 Med: 231799.0000 Stdev: 7007.6800	0.8902	4.8500
BenchmarkBSONFlatDocumentEncoding	total_bytes_allocated	14.5871	548957360.0000	Avg: 479074249.7699 Med: 479913704.0000 Stdev: 14431557.6550	0.8900	4.8424
BenchmarkBSONFullDocumentDecoding	total_mem_allocs	14.4795	10044222.0000	Avg: 8773820.6042 Med: 8779734.5000 Stdev: 288604.3175	0.8907	4.4019
BenchmarkBSONFullDocumentEncoding	total_bytes_allocated	11.3008	270292128.0000	Avg: 242848379.7522 Med: 242696304.0000 Stdev: 4809646.2804	0.9080	5.7060
BenchmarkBSONDeepDocumentEncoding	total_mem_allocs	6.1892	235280.0000	Avg: 221566.8407 Med: 222611.0000 Stdev: 5710.6696	0.7789	2.4013
BenchmarkBSONDeepDocumentEncoding	total_bytes_allocated	6.0998	167701848.0000	Avg: 158060451.2566 Med: 158826416.0000 Stdev: 4081994.8518	0.7770	2.3619
BenchmarkBSONDeepDocumentEncoding	ns_per_op	-5.8332	15295.0000	Avg: 16242.4602 Med: 16170.0000 Stdev: 429.8394	0.7613	-2.2042
BenchmarkBSONFullDocumentEncoding	total_mem_allocs	2.7863	1561856.0000	Avg: 1519518.0000 Med: 1519518.0000 Stdev: 11602.2081	0.9031	3.6491
BenchmarkBSONFullDocumentDecoding	ns_per_op	-1.7321	73073.0000	Avg: 74361.0000 Med: 74361.0000 Stdev: 67.8823	0.9814	-18.9740
BenchmarkBSONFullDocumentEncoding	ns_per_op	-1.2220	23279.0000	Avg: 23567.0000 Med: 23567.0000 Stdev: 21.2132	0.9740	-13.5765
BenchmarkBSONFlatDocumentEncoding	allocated_bytes_per_op	-0.1070	6265.0000	Avg: 6271.7080 Med: 6272.0000 Stdev: 2.8806	0.7656	-2.3287
BenchmarkSingleRunCommand	allocated_bytes_per_op	-0.0939	12186.0000	Avg: 12197.4583 Med: 12197.0000 Stdev: 5.3154	0.7521	-2.1557
BenchmarkBSONFullDocumentDecoding	allocated_bytes_per_op	0.0253	25330.0000	Avg: 25323.6042 Med: 25324.0000 Stdev: 1.0865	0.9144	5.8868

For a comprehensive view of all microbenchmark results for this PR's commit, please check out the Evergreen perf task for this patch.

[mongodb-drivers-pr-bot]

API Change Report

No changes found!

[Copilot]

Pull Request Overview

This pull request drops support for MongoDB 4.0, updating the minimum supported MongoDB version to 4.2.

• Updated minimum wire version from 7 (MongoDB 4.0) to 8 (MongoDB 4.2)
• Removed version checks and constraints for MongoDB 4.0 throughout the codebase
• Added skip entries for pre-4.2 SDAM tests that are no longer relevant

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
x/mongo/driver/topology/topology_test.go	Updated error message to reflect new minimum wire version requirement
x/mongo/driver/topology/sdam_spec_test.go	Added CheckSkip call to skip irrelevant pre-4.2 tests
x/mongo/driver/topology/fsm.go	Updated MinSupportedMongoDBVersion constant from "4.0" to "4.2"
x/mongo/driver/integration/scram_test.go	Removed MongoDB 4.0 version check and unused import
mongo/options/listcollectionsoptions.go	Removed MongoDB 4.0 version constraint from documentation
mongo/options/changestreamoptions.go	Removed MongoDB 4.0 version constraint from documentation
internal/spectest/skip.go	Added skip entries for pre-4.2 SDAM tests
internal/integration/sdam_error_handling_test.go	Removed MongoDB 4.0 version constraints from test options
internal/integration/primary_stepdown_test.go	Simplified test cases by removing version constraints
internal/integration/change_stream_test.go	Removed MongoDB 4.0 specific test cases and helper functions
internal/driverutil/description.go	Updated MinWireVersion constant from 7 to 8
internal/docexamples/examples_test.go	Simplified causal consistency examples by removing version filtering
README.md	Updated documentation to reflect MongoDB 4.2 as minimum version
.evergreen/config.yml	Removed MongoDB 4.0 build variants from CI configuration

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