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Note when trait bound may be satisfied for a different version of a crate #78552

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Aaron1011 opened this issue Oct 30, 2020 · 2 comments
Open

Note when trait bound may be satisfied for a different version of a crate #78552

Aaron1011 opened this issue Oct 30, 2020 · 2 comments
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A-diagnostics Area: Messages for errors, warnings, and lints A-traits Area: Trait system D-confusing Diagnostics: Confusing error or lint that should be reworked. D-crate-version-mismatch Diagnostics: Errors or lints caused be the use of two different crate versions. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@Aaron1011
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On the playground, the following code:

use bytes::Bytes;
use http::Response;
use hyper::Body;

pub fn build(data: Bytes) -> Response<Body> {
    Response::new(data.into())
}

fn main() {
}

currently produces the following error:

error[E0277]: the trait bound `hyper::Body: std::convert::From<bytes::Bytes>` is not satisfied
 --> src/main.rs:6:19
  |
6 |     Response::new(data.into())
  |                   ^^^^^^^^^^^ the trait `std::convert::From<bytes::Bytes>` is not implemented for `hyper::Body`
  |
  = help: the following implementations were found:
            <hyper::Body as std::convert::From<&'static [u8]>>
            <hyper::Body as std::convert::From<&'static str>>
            <hyper::Body as std::convert::From<hyper::body::Bytes>>
            <hyper::Body as std::convert::From<std::borrow::Cow<'static, [u8]>>>
          and 4 others
  = note: required because of the requirements on the impl of `std::convert::Into<hyper::Body>` for `bytes::Bytes`

Note that hyper::body::Bytes is an alias for bytes::Bytes. We should detect when an unment trait bound's substs match the fully-qualified names of our desired trait bound, and note that multiple versions of the same crate may be in use.
@Aaron1011 Aaron1011 added A-traits Area: Trait system T-community D-confusing Diagnostics: Confusing error or lint that should be reworked. D-crate-version-mismatch Diagnostics: Errors or lints caused be the use of two different crate versions. labels Oct 30, 2020
@Aaron1011
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This is similar to #73560, but it occurs in a different part of the compiler.

@jyn514
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jyn514 commented Oct 30, 2020

A similar error:

error[E0277]: a value of type `HashMap<std::string::String, cargo_metadata::Package>` cannot be built from an iterator over elements of type `(std::string::String, cargo_metadata::Package)`
  --> src/utils/cargo_metadata.rs:46:18
   |
46 |                 .collect(),
   |                  ^^^^^^^ value of type `HashMap<std::string::String, cargo_metadata::Package>` cannot be built from `std::iter::Iterator<Item=(std::string::String, cargo_metadata::Package)>`
   |
   = help: the trait `FromIterator<(std::string::String, cargo_metadata::Package)>` is not implemented for `HashMap<std::string::String, cargo_metadata::Package>`

The first cargo_metadata is a module, the second is a crate.

@Aaron1011 Aaron1011 added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. and removed T-community labels Oct 30, 2020
@camelid camelid added the A-diagnostics Area: Messages for errors, warnings, and lints label Oct 30, 2020
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A-diagnostics Area: Messages for errors, warnings, and lints A-traits Area: Trait system D-confusing Diagnostics: Confusing error or lint that should be reworked. D-crate-version-mismatch Diagnostics: Errors or lints caused be the use of two different crate versions. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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