The assertion documents that PathBuf::join discards its base when handed an
absolute path — which is why confinement has to happen after the join, not
instead of it. clippy::join_absolute_paths flags that shape, correctly for
production code, so the lint is allowed here rather than the test weakened.
Worth recording: this lint would not have caught the original defect. The real
join sites pass a variable, and it only fires on a literal.
dtourolle
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