{"action":"created","issue":{"url":"https://api.github.com/repos/rust-lang/rust/issues/55516","repository_url":"https://api.github.com/repos/rust-lang/rust","labels_url":"https://api.github.com/repos/rust-lang/rust/issues/55516/labels{/name}","comments_url":"https://api.github.com/repos/rust-lang/rust/issues/55516/comments","events_url":"https://api.github.com/repos/rust-lang/rust/issues/55516/events","html_url":"https://github.com/rust-lang/rust/issues/55516","id":375679526,"node_id":"MDU6SXNzdWUzNzU2Nzk1MjY=","number":55516,"title":"`write!` is somehow masking the `#[must_use]` on its result","user":{"login":"pnkfelix","id":173127,"node_id":"MDQ6VXNlcjE3MzEyNw==","avatar_url":"https://avatars0.githubusercontent.com/u/173127?v=4","gravatar_id":"","url":"https://api.github.com/users/pnkfelix","html_url":"https://github.com/pnkfelix","followers_url":"https://api.github.com/users/pnkfelix/followers","following_url":"https://api.github.com/users/pnkfelix/following{/other_user}","gists_url":"https://api.github.com/users/pnkfelix/gists{/gist_id}","starred_url":"https://api.github.com/users/pnkfelix/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/pnkfelix/subscriptions","organizations_url":"https://api.github.com/users/pnkfelix/orgs","repos_url":"https://api.github.com/users/pnkfelix/repos","events_url":"https://api.github.com/users/pnkfelix/events{/privacy}","received_events_url":"https://api.github.com/users/pnkfelix/received_events","type":"User","site_admin":false},"labels":[{"id":262252840,"node_id":"MDU6TGFiZWwyNjIyNTI4NDA=","url":"https://api.github.com/repos/rust-lang/rust/labels/regression-from-stable-to-stable","name":"regression-from-stable-to-stable","color":"e4008a","default":false}],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2018-10-30T20:29:42Z","updated_at":"2018-10-30T20:32:38Z","closed_at":null,"author_association":"MEMBER","body":"Hat tip to @shepmaster for finding this\r\n\r\n[play](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2015&gist=267a47eba842626f4cce618ad89caa47)\r\n\r\n```rust\r\nfn main() {\r\n    use std::fmt::Write;\r\n    let mut example = String::new();\r\n    write!(&mut example, \"{}\", 42);\r\n}\r\n```\r\n\r\nis not triggering the `#[must_use]` lint on `Result`."},"comment":{"url":"https://api.github.com/repos/rust-lang/rust/issues/comments/434458742","html_url":"https://github.com/rust-lang/rust/issues/55516#issuecomment-434458742","issue_url":"https://api.github.com/repos/rust-lang/rust/issues/55516","id":434458742,"node_id":"MDEyOklzc3VlQ29tbWVudDQzNDQ1ODc0Mg==","user":{"login":"shepmaster","id":174509,"node_id":"MDQ6VXNlcjE3NDUwOQ==","avatar_url":"https://avatars0.githubusercontent.com/u/174509?v=4","gravatar_id":"","url":"https://api.github.com/users/shepmaster","html_url":"https://github.com/shepmaster","followers_url":"https://api.github.com/users/shepmaster/followers","following_url":"https://api.github.com/users/shepmaster/following{/other_user}","gists_url":"https://api.github.com/users/shepmaster/gists{/gist_id}","starred_url":"https://api.github.com/users/shepmaster/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/shepmaster/subscriptions","organizations_url":"https://api.github.com/users/shepmaster/orgs","repos_url":"https://api.github.com/users/shepmaster/repos","events_url":"https://api.github.com/users/shepmaster/events{/privacy}","received_events_url":"https://api.github.com/users/shepmaster/received_events","type":"User","site_admin":false},"created_at":"2018-10-30T20:32:38Z","updated_at":"2018-10-30T20:32:38Z","author_association":"MEMBER","body":"This code compiles with warnings in Rust 1.28.0, but no warnings in Rust 1.29.0\r\n\r\n```rust\r\nfn main() {\r\n    use std::fmt::Write;\r\n    let mut example = String::new();\r\n    write!(&mut example, \"{}\", 42);\r\n}\r\n```\r\n\r\n```\r\n$ cargo +1.28.0 build\r\n   Compiling xz v0.1.0 (file:///private/tmp/xz)\r\nwarning: unused `std::result::Result` which must be used\r\n --> src/main.rs:4:5\r\n  |\r\n4 |     write!(&mut example, \"{}\", 42);\r\n  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  |\r\n  = note: #[warn(unused_must_use)] on by default\r\n  = note: this `Result` may be an `Err` variant, which should be handled\r\n  = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)\r\n\r\n    Finished dev [unoptimized + debuginfo] target(s) in 1.02s\r\n\r\n$ cargo clean\r\n$ cargo +1.29.0 build\r\n   Compiling xz v0.1.0 (file:///private/tmp/xz)\r\n    Finished dev [unoptimized + debuginfo] target(s) in 1.09s\r\n```\r\n\r\nPotentially related to #54288."}}
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