为什么用git哈希替换依赖项的版本和路径属性会导致编译错误？

Question

我有一个奇怪的依赖问题。以下是重现的步骤：

❯ rustc -V
rustc 1.35.0-nightly (82e2f3ec2 2019-03-20)

❯ git clone https://github.com/google/tarpc.git
❯ cd tarpc/example-service

❯ cargo build
    Finished dev [unoptimized + debuginfo] target(s) in 0.13s

❯ git rev-parse HEAD
06544faa5a0872d4be989451afc0a2b1e1278df4

现在我替换Cargo.toml中的一行

bincode-transport = { package = "tarpc-bincode-transport", version = "0.3", path = "../bincode-transport" }

至

bincode-transport = { package = "tarpc-bincode-transport", git="https://github.com/google/tarpc.git", rev="06544faa5a0872d4be989451afc0a2b1e1278df4" }

代表相同的代码库（我认为version = 0.3毫无意义），

然后我有一个构建错误

❯ cargo build
    Blocking waiting for file lock on the git checkouts
    Updating git repository `https://github.com/google/tarpc.git`
   Compiling tarpc-example-service v0.2.0 (tarpc/example-service)
error[E0277]: the trait bound `tarpc_bincode_transport::Transport<tokio_tcp::stream::TcpStream, _, _>: tarpc_lib::transport::Transport` is not satisfied
  --> example-service/src/server.rs:45:4
   |
45 |         .incoming(transport)
   |          ^^^^^^^^ the trait `tarpc_lib::transport::Transport` is not implemented for `tarpc_bincode_transport::Transport<tokio_tcp::stream::TcpStream, _, _>`

error[E0277]: the trait bound `tarpc_bincode_transport::Transport<tokio_tcp::stream::TcpStream, _, _>: tarpc_lib::transport::Transport` is not satisfied
  --> example-service/src/client.rs:20:29
   |
20 |     let mut client = await!(service::new_stub(client::Config::default(), transport))?;
   |                             ^^^^^^^^^^^^^^^^^ the trait `tarpc_lib::transport::Transport` is not implemented for `tarpc_bincode_transport::Transport<tokio_tcp::stream::TcpStream, _, _>`
   |
   = note: required by `service::new_stub`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
error: Could not compile `tarpc-example-service`.
warning: build failed, waiting for other jobs to finish...
error[E0599]: no method named `respond_with` found for type `impl futures_core::stream::Stream` in the current scope
  --> example-service/src/server.rs:48:4
   |
48 |         .respond_with(service::serve(HelloServer));
   |          ^^^^^^^^^^^^
   |
   = note: the method `respond_with` exists but the following trait bounds were not satisfied:
           `&impl futures_core::stream::Stream : tarpc_lib::server::Handler<_, _, _>`
           `&mut impl futures_core::stream::Stream : tarpc_lib::server::Handler<_, _, _>`
           `impl futures_core::stream::Stream : tarpc_lib::server::Handler<_, _, _>`

error: aborting due to 2 previous errors

Some errors occurred: E0277, E0599.
For more information about an error, try `rustc --explain E0277`.
error: Could not compile `tarpc-example-service`.

cargo clean没有帮助。这怎么可能？

Answer 1

这是与Why is a trait not implemented for a type that clearly has it implemented?相同的问题 - 通过拉入代码的git版本和代码的本地版本（通过tarpc = { path = "../tarpc" }），你正在编译tarpc箱子两次不同。每个特征彼此不同，它们实际上是同一个箱子的不同版本。

这可以使用cargo tree -d -i验证：

tarpc-lib v0.2.0 (https://github.com/google/tarpc.git?rev=06544faa5a0872d4be989451afc0a2b1e1278df4#06544faa)
└── tarpc-bincode-transport v0.3.0 (https://github.com/google/tarpc.git?rev=06544faa5a0872d4be989451afc0a2b1e1278df4#06544faa)
    └── tarpc-example-service v0.2.0 (/private/tmp/tarpc/example-service)

tarpc-lib v0.2.0 (/private/tmp/tarpc/rpc)
└── tarpc v0.14.1 (/private/tmp/tarpc/tarpc)
    └── tarpc-example-service v0.2.0 (/private/tmp/tarpc/example-service)

tarpc-trace v0.1.0 (https://github.com/google/tarpc.git?rev=06544faa5a0872d4be989451afc0a2b1e1278df4#06544faa)
└── tarpc-lib v0.2.0 (https://github.com/google/tarpc.git?rev=06544faa5a0872d4be989451afc0a2b1e1278df4#06544faa)
    └── tarpc-bincode-transport v0.3.0 (https://github.com/google/tarpc.git?rev=06544faa5a0872d4be989451afc0a2b1e1278df4#06544faa)
        └── tarpc-example-service v0.2.0 (/private/tmp/tarpc/example-service)

tarpc-trace v0.1.0 (/private/tmp/tarpc/trace)
└── tarpc-lib v0.2.0 (/private/tmp/tarpc/rpc)
    └── tarpc v0.14.1 (/private/tmp/tarpc/tarpc)
        └── tarpc-example-service v0.2.0 (/private/tmp/tarpc/example-service)

如果你一直使用git中的版本，它将工作：

tarpc = { git = "https://github.com/google/tarpc.git", rev = "06544faa5a0872d4be989451afc0a2b1e1278df4", features = ["serde1"] }