From 911de7b98c828ddf18fc6a1db227593faee7aad3 Mon Sep 17 00:00:00 2001 From: Guillaume Gomez Date: Mon, 28 Feb 2022 14:23:11 +0100 Subject: [PATCH 1/2] Add explanation for E0726 --- compiler/rustc_error_codes/src/error_codes.rs | 2 +- .../src/error_codes/E0726.md | 46 +++++++++++++++++++ 2 files changed, 47 insertions(+), 1 deletion(-) create mode 100644 compiler/rustc_error_codes/src/error_codes/E0726.md diff --git a/compiler/rustc_error_codes/src/error_codes.rs b/compiler/rustc_error_codes/src/error_codes.rs index a72681dbf4e7e..a185902123d8a 100644 --- a/compiler/rustc_error_codes/src/error_codes.rs +++ b/compiler/rustc_error_codes/src/error_codes.rs @@ -429,6 +429,7 @@ E0720: include_str!("./error_codes/E0720.md"), E0722: include_str!("./error_codes/E0722.md"), E0724: include_str!("./error_codes/E0724.md"), E0725: include_str!("./error_codes/E0725.md"), +E0726: include_str!("./error_codes/E0726.md"), E0727: include_str!("./error_codes/E0727.md"), E0728: include_str!("./error_codes/E0728.md"), E0729: include_str!("./error_codes/E0729.md"), @@ -641,6 +642,5 @@ E0787: include_str!("./error_codes/E0787.md"), E0717, // rustc_promotable without stability attribute // E0721, // `await` keyword // E0723, // unstable feature in `const` context - E0726, // non-explicit (not `'_`) elided lifetime in unsupported position // E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`. } diff --git a/compiler/rustc_error_codes/src/error_codes/E0726.md b/compiler/rustc_error_codes/src/error_codes/E0726.md new file mode 100644 index 0000000000000..e3794327f2d4d --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0726.md @@ -0,0 +1,46 @@ +An argument lifetime was elided in an async function. + +Erroneous code example: + +When a struct or a type is bound/declared with a lifetime it is important for +the Rust compiler to know, on usage, the lifespan of the type. When the +lifetime is not explicitly mentioned and the Rust Compiler cannot determine +the lifetime of your type, the following error occurs. + +```compile_fail,E0726 +use futures::executor::block_on; +struct Content<'a> { + title: &'a str, + body: &'a str, +} +async fn create(content: Content) { // error: implicit elided + // lifetime not allowed here + println!("title: {}", content.title); + println!("body: {}", content.body); +} +let content = Content { title: "Rust", body: "is great!" }; +let future = create(content); +block_on(future); +``` + +Specify desired lifetime of parameter `content` or indicate the anonymous +lifetime like `content: Content<'_>`. The anonymous lifetime tells the Rust +compiler that `content` is only needed until create function is done with +it's execution. + +The `implicit elision` meaning the omission of suggested lifetime that is +`pub async fn create<'a>(content: Content<'a>) {}` is not allowed here as +lifetime of the `content` can differ from current context: + +```ignore (needs futures dependency) +async fn create(content: Content<'_>) { // ok! + println!("title: {}", content.title); + println!("body: {}", content.body); +} +``` + +Know more about lifetime elision in this [chapter][lifetime-elision] and a +chapter on lifetimes can be found [here][lifetimes]. + +[lifetime-elision]: https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html#lifetime-elision +[lifetimes]: https://doc.rust-lang.org/rust-by-example/scope/lifetime.html From 8f36d4a536fd194a3f412e957e176cf2944d9c0a Mon Sep 17 00:00:00 2001 From: Guillaume Gomez Date: Mon, 28 Feb 2022 14:37:27 +0100 Subject: [PATCH 2/2] Update ui test with the add of E0726 explanation --- src/test/ui/async-await/async-fn-path-elision.stderr | 1 + src/test/ui/impl-header-lifetime-elision/path-elided.stderr | 1 + src/test/ui/impl-header-lifetime-elision/trait-elided.stderr | 1 + src/test/ui/issues/issue-10412.stderr | 3 ++- src/test/ui/wf/wf-in-foreign-fn-decls-issue-80468.stderr | 1 + 5 files changed, 6 insertions(+), 1 deletion(-) diff --git a/src/test/ui/async-await/async-fn-path-elision.stderr b/src/test/ui/async-await/async-fn-path-elision.stderr index 36fb73a8dde24..3d18d9c412596 100644 --- a/src/test/ui/async-await/async-fn-path-elision.stderr +++ b/src/test/ui/async-await/async-fn-path-elision.stderr @@ -8,3 +8,4 @@ LL | async fn error(lt: HasLifetime) { error: aborting due to previous error +For more information about this error, try `rustc --explain E0726`. diff --git a/src/test/ui/impl-header-lifetime-elision/path-elided.stderr b/src/test/ui/impl-header-lifetime-elision/path-elided.stderr index 1c81c69620165..90522a885ab90 100644 --- a/src/test/ui/impl-header-lifetime-elision/path-elided.stderr +++ b/src/test/ui/impl-header-lifetime-elision/path-elided.stderr @@ -8,3 +8,4 @@ LL | impl MyTrait for Foo { error: aborting due to previous error +For more information about this error, try `rustc --explain E0726`. diff --git a/src/test/ui/impl-header-lifetime-elision/trait-elided.stderr b/src/test/ui/impl-header-lifetime-elision/trait-elided.stderr index 735f01379f09f..15bc3f106b9c4 100644 --- a/src/test/ui/impl-header-lifetime-elision/trait-elided.stderr +++ b/src/test/ui/impl-header-lifetime-elision/trait-elided.stderr @@ -8,3 +8,4 @@ LL | impl MyTrait for u32 { error: aborting due to previous error +For more information about this error, try `rustc --explain E0726`. diff --git a/src/test/ui/issues/issue-10412.stderr b/src/test/ui/issues/issue-10412.stderr index 053a93e6cd8c7..a91b3c90ebb25 100644 --- a/src/test/ui/issues/issue-10412.stderr +++ b/src/test/ui/issues/issue-10412.stderr @@ -67,4 +67,5 @@ LL | trait Serializable<'self, T: ?Sized> { error: aborting due to 9 previous errors -For more information about this error, try `rustc --explain E0277`. +Some errors have detailed explanations: E0277, E0726. +For more information about an error, try `rustc --explain E0277`. diff --git a/src/test/ui/wf/wf-in-foreign-fn-decls-issue-80468.stderr b/src/test/ui/wf/wf-in-foreign-fn-decls-issue-80468.stderr index d3593d8c1eb67..ba624507c21f0 100644 --- a/src/test/ui/wf/wf-in-foreign-fn-decls-issue-80468.stderr +++ b/src/test/ui/wf/wf-in-foreign-fn-decls-issue-80468.stderr @@ -30,3 +30,4 @@ LL | impl Trait for Ref {} error: aborting due to 2 previous errors +For more information about this error, try `rustc --explain E0726`.