Provide optional Read/Write methods for stdio

[thaliaarchi]

Override more of the default methods for io::Read and io::Write for stdio types, when efficient to do so, and deduplicate unsupported types.

Tracked in #136756.

[rustbot]

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[thaliaarchi]

@joboet Looks like you wrote #136780 to have minimum conflicts to this. Thanks for that. I don't mind rebasing onto that, if yours is merged first.

[Noratrieb]

r? joboet

[thaliaarchi]

I dropped a few commits from this PR:

• 5da7fbe (Fix unsafe_op_in_unsafe_fn for TEEOS), because Apply unsafe_op_in_unsafe_fn to the standard library #136986 is in the merge queue
• 1a08321 (Deduplicate unsupported fs.rs for UEFI) per Nora's note
• 1b05019 (Remove unused methods on Hermit FileDesc), because that would be a better fit for a file-focused PR.

[thaliaarchi]

Since this touches a lot of targets, I'm going to split this into multiple PRs for more target-focused review, once #136780 goes through the merge queue.

[joboet]

Since this touches a lot of targets, I'm going to split this into multiple PRs for more target-focused review, once #136780 goes through the merge queue.

That'd be great, thank you! Especially the SGX stuff would be much simpler to review as a dedicated PR.

[thaliaarchi]

@joboet Would you mind rebasing #136780 onto master so it can be merged and we can move forward with this?

[thaliaarchi]

Now that #136780 has merged, we're ready for review again!

I've moved anything platform-specific out of this PR. #137355 is for SGX, #138301 is for Hermit, and I will open one for Xous after this merges. Everything else that was split out of this PR has already been merged.

@rustbot review

[thaliaarchi]

That being said, I copy the optional I/O methods to std::sys::stdio::unsupported which I add to std::io::Empty in #137051, which means any feedback from there will apply here. But, since this hasn't been reviewed in a while or without all the more platform-specific parts, a review here would still be helpful.

[thaliaarchi]

@rustbot label -O-hermit -O-SGX -O-solid -O-unix -O-wasi -O-wasm -O-windows

[joboet]

Just some cosmetic suggestions:

[joboet]

I think making Stderr an alias to Stdin in some of the other modules is a clever idea. Perhaps you could do the same here?

[thaliaarchi]

Sure, I can do that. I think the only downside to these aliases is that Stderr is then misnamed as Stdout in stack traces.

[thaliaarchi]

Thanks for the review! I've updated to address your feedback.

@rustbot blocked (on #137051)