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Type:
Bug
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Resolution: Fixed
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: Internal Code
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None
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Fully Compatible
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ALL
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v4.4
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Service arch 2020-04-20
`fmt::formatter::format` writes into and advances an output iterator obtained by `ctx.out()`. It has to return the advanced output iterator. But we return the `ctx.out()`, not the copy we advanced.
This yielded UB in a toolchain validation build against mongo 4.2 on
“Amazon Linux 1 2018.03" the build image.
[https://logkeeper.mongodb.org/lobster/build/24a6f9b5ad70e8fbfc9bed6e0ccf388e/test/5e8a1e02be07c446740c1d7f#bookmarks=0%2C19%2C67
]
[cpp_unit_test:network_test] 2020-04-05T18:05:54.634+0000 2020-04-05T18:05:54.634+0000 E - [main] Throwing exception: Expected fmt::format("{}", hp) == hps (1.2.3.4:2\0\0\0\0 == 1.2.3.4:27017) @src/mongo/util/net/hostandport_test.cpp:139
[cpp_unit_test:network_test] 2020-04-05T18:05:54.634+0000 2020-04-05T18:05:54.634+0000 I - [main] FAIL: Fmt Expected fmt::format("{}", hp) == hps (1.2.3.4:2\0\0\0\0 == 1.2.3.4:27017) @src/mongo/util/net/hostandport_test.cpp:139 in test Fmt