Question

我的代码曾经在夜间工作 - 2016-11-15。当我升级到1.15.1稳定版时，我开始收到一些关于未找到类型实现的错误。这是一个例子：

error[E0277]: the trait bound `errors::Error: core::convert::From<r2d2_postgres::<unnamed>::error::Error>` is not satisfied
  --> src/pg/datastore.rs:79:23
   |
79 |         let results = conn.query("DELETE FROM accounts WHERE id=$1 RETURNING 1", &[&account_id])?;
   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `core::convert::From<r2d2_postgres::<unnamed>::error::Error>` is not implemented for `errors::Error`
   |
   = help: the following implementations were found:
   = help:   <errors::Error as core::convert::From<r2d2_postgres::Error>>
   = help:   <errors::Error as core::convert::From<postgres::error::Error>>
   = help:   <errors::Error as core::convert::From<r2d2::GetTimeout>>
   = help:   <errors::Error as core::convert::From<rocksdb::Error>>
   = help: and 3 others
   = note: required by `core::convert::From::from`

......即使有相关的From实施。这是一个缩短版本：

use std::error::Error as StdError;
use r2d2::GetTimeout;
use postgres::error::Error as PostgresError;
use r2d2_postgres::Error as R2D2PostgresError;
use super::fmt;

#[derive(Eq, PartialEq, Clone, Debug)]
pub enum Error {
    Unexpected(String),
    ...
}

impl StdError for Error {
    fn description(&self) -> &str {
        ...
    }

    fn cause(&self) -> Option<&StdError> {
        None
    }
}

impl From<R2D2PostgresError> for Error {
    fn from(err: R2D2PostgresError) -> Error {
        Error::Unexpected(format!("{}", err))
    }
}

impl From<PostgresError> for Error {
    fn from(err: PostgresError) -> Error {
        Error::Unexpected(pg_error_to_description(err))
    }
}

impl From<GetTimeout> for Error {
    fn from(err: GetTimeout) -> Error {
        Error::Unexpected(format!("Could not fetch connection: {}", err))
    }
}

我认为这与使用相关类型有关，因为它似乎不会在其他环境中发生。此外，命名空间r2d2_postgres::<unnamed>::error::Error没有意义 - 什么是<unnamed>？这是the relevant type association。

Answer 1

原来这是由于版本冲突造成的。我已切换到postgres的主分支以修复单独的版本冲突，但r2d2_postgres引用了不同版本的postgres。

幸运的是，正如this issue中所述，Cargo.toml有一个[replace]部分，可让您像这样处理它：

[replace]
"postgres:0.13.6" = { git = "https://github.com/sfackler/rust-postgres" }

无法找到关联类型的特征实现

1 个答案: