Move pal::env to std::sys::env_consts

[thaliaarchi]

Combine the std::env::consts platform implementations as a single file. Use the Unix file as the base, since it has 28 entries, and fold the 8 singleton platforms into it. The Unix file was roughly grouped into Linux, Apple, BSD, and everything else, roughly in alphabetical order. Alphabetically order them to make it easier to maintain and discard the Unix-specific groups to generalize it to all platforms.

I'd prefer to have no fallback implementation, as I consider it a bug; however TEEOS, Trusty, and Xous have no definitions here. Since they otherwise have pal abstractions, that indicates that there are several platforms without pal abstractions which are also missing here. To support unsupported, create a little macro to handle the fallback case and not introduce ordering between the cfgs like cfg_if!.

I've named the module std::sys::env_consts, because they are used in std::env::consts and I intend to use the name std::sys::env for the combination of Args and Vars.

cc @joboet @ChrisDenton

Tracked in #117276.

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[thaliaarchi]

Commit 87339da is an earlier version which used cfg_if!. I don't like the ordering between the cfgs that it introduces.

[thaliaarchi]

WALI presents a complication, because it's both Linux and Wasm, but it's probably just as simple as #[cfg(all(target_family = "wasm", not(target_os = "linux")))]. The only others which don't gate on target_os are #[cfg(all(target_vendor = "fortanix", target_env = "sgx"))] and #[windows]. SGX is easy to verify, since there's only one target. For Windows, I've expanded #[windows] to #[cfg(target_family = "windows")], since that's what it's a shorthand for, though #[cfg(target_os = "windows")] would be more clear. According to @ChrisDenton, there's probably not any cases where they differ.

[joboet]

Sound and looks good to me!
@bors r+

[bors]

📌 Commit cac458c has been approved by joboet

It is now in the queue for this repository.

[matthiaskrgr]

@bors r-
#140012 (comment)

2025-04-18T20:16:55.6950825Z
2025-04-18T20:16:55.8638464Z error[E0428]: the name `os` is defined multiple times
2025-04-18T20:16:55.8639221Z    --> library/std/src/sys/env_consts.rs:362:1
2025-04-18T20:16:55.8639750Z     |
2025-04-18T20:16:55.8640277Z 65  | pub mod os {
2025-04-18T20:16:55.8641094Z     | ---------- previous definition of the module `os` here
2025-04-18T20:16:55.8641700Z ...
2025-04-18T20:16:55.8642184Z 362 | pub mod os {
2025-04-18T20:16:55.8642884Z     | ^^^^^^^^^^ `os` redefined here
2025-04-18T20:16:55.8643648Z     |
2025-04-18T20:16:55.8644365Z     = note: `os` must be defined only once in the type namespace of this module
2025-04-18T20:16:55.8644825Z
2025-04-18T20:16:58.4808620Z For more information about this error, try `rustc --explain E0428`.
2025-04-18T20:16:58.5006460Z [RUSTC-TIMING] std test:false 2.826
2025-04-18T20:16:58.5009351Z warning: `std` (lib) generated 1 warning
2025-04-18T20:16:58.5010054Z error: could not compile `std` (lib) due to 1 previous error; 1 warning emitted
2025-04-18T20:16:58.5068975Z Build completed unsuccessfully in 0:00:34
2025-04-18T20:16:58.5157722Z   local time: Fri Apr 18 20:16:58 UTC 2025
2025-04-18T20:16:58.5715563Z   network time: Fri, 18 Apr 2025 20:16:58 GMT
``

[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

[thaliaarchi]

I've fixed Emscripten (which failed CI).

Also, I confirmed that target_os = "emscripten" always implies target_arch = "wasm32" and that target_family = "windows" iff target_os = "windows, so I switched those two to just target_os to make them more clear. Now, only Wasm and SGX aren't gated using target_os and I've similarly verified that they're mutually exclusive with the others.

$ rustc +nightly -Z unstable-options --print all-target-specs-json > targets.json
$ jq 'to_entries[] | select(.value | .os == "emscripten" and .arch != "wasm32")' targets.json
$ jq 'to_entries[] | select(.value | (."target-family" // [] | contains(["windows"])) != (.os == "windows"))' targets.json
$ jq 'map(select(."target-family" // [] | contains(["wasm"])).os) | unique[]' targets.json
null
"emscripten"
"linux"
"unknown"
"wasi"
$ jq '.[] | select(.vendor == "fortanix" or .env == "sgx").os' targets.json
"unknown"

In the process of this exploration, I found two tiny code simplifications in rustc_targets to match the style of other targets.

[thaliaarchi]

The macro is now much simpler, while doing the same thing.

@rustbot ready

[joboet]

Neat!
@bors r+

[bors]

📌 Commit 93fa96c has been approved by joboet

It is now in the queue for this repository.