std::io::Read incorrectly has no marked required methods

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https://doc.rust-lang.org/std/io/trait.Read.html

Summary

The base read method is marked as "provided" in the current method list, which is inconsistent with the rest of the documentation:

Readers are defined by one required method, read()

@rustbot

Technically at least one of read or the unstable read_buf must be implemented, and the default implementations of those methods use each other. You can see this in the error message when you fail to implement them:

error[E0046]: not all trait items implemented, missing one of: `read_buf`, `read`
  --> src/main.rs:16:1
   |
16 | impl std::io::Read for MyStruct {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing one of `read_buf`, `read` in implementation

Because both of these methods have a default implementation, they're not considered "required" by rustdoc. It should probably parse #[rustc_must_implement_one_of(read_buf, read)] and display this somehow (no idea how to concisely represent this).

@rustbot label +T-rustdoc -needs-triage

@rustbot

@rustbot claim

@AlaskanEmily

@AlaskanEmily @asquared31415 when a trait has #[rustc_must_implement_one_of], show the
"Required Methods" entry in the sidebar (linking to the existing section).
Would you also want the declaration comment changed, or is the sidebar
enough?

This issue was already kinda solved. Opened #164266 to cover the missing bits.

Rollup merge of rust-lang#164266 - GuillaumeGomez:rustc_must_implemen…

Unrolled build for #164266 in rollup 164322

Rollup merge of #164266 - GuillaumeGomez:rustc_must_implement_one_of,…

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std::io::Read incorrectly has no marked required methods #163675

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std::io::Read incorrectly has no marked required methods #163675

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asquared31415 commented on Oct 2, 2026

integral-830 commented on Oct 4, 2026

integral-830 commented on Oct 5, 2026

GuillaumeGomez commented on Oct 13, 2026

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