Jacob Pratt
3f19aa5672
docs: clarify path search behavior in std::process::Command::new the existing docs mentioned that `PATH` is searched in an "os defined way" and that it could be controlled by setting PATH on the command but never explained which `PATH` is actually used. on unix the key thing to understand is that when you modify the childs environment (via `env()`, `env_remove()`, or `env_clear()`), the `PATH` search uses whatever `PATH` ends up in the child's environment not the parents. so if you call `env_clear()` and forget to set `PATH`, you don't get the parents `PATH` as a fallback; you get the OS default (typically `/bin:/usr/bin`) which often won't find what you need. the three cases are now documented: - unmodified env: child inherits parents `PATH`, that gets searched - `PATH` explicitly set `via env()`: the new value is searched - `PATH` removed (`env_clear` or `env_remove`): falls back to OS default, not the parents `PATH` on windows rust resolves the executable before spawning rather than letting `CreateProcessW` do it. the search order is: childs `PATH` (if explicitly set) first then system-defined directories then the parents `PATH`. the existing note about issue rust-lang/rust#37519 is preserved. limitations in this doc: - the unix fallback path behavior ("typically `/bin:/usr/bin`") is verified for linux/glibc. behavior on macOS, BSD, and musl is similar in practice but not fully confirmed here. - the windows search order is summarized as "system-defined directories" which actually includes the application directory (the directory of the calling process's executable) as a distinct step before the system dirs that detail is omitted for brevity. - `posix_spawnp` `PATH` source (calling process environ vs envp argument) is ambiguous in the `POSIX` spec; the behavior here is inferred from the guard in `unix.rs` that bypasses `posix_spawn` when `PATH` has been modified. closes rust-lang/rust#137286 (hopefully)
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