問題描述

clickhouse 的原生 rust 客戶端目前比較好的有兩個clickhouse-rs和 clickhouse.rs。

clickhouse-rs 是 tcp 連接；clickhouse.rs 是 http 連接。

兩個庫在單獨使用時沒有任何問題，但是，在同一工程同時引用時會報錯。

Cargo.toml

# clickhouse http
clickhouse = {git = "https://github.com/loyd/clickhouse.rs", features =      ["test-util"]}


# clickhouse tcp
clickhouse-rs={git="https://github.com/suharev7/clickhouse-rs",features=["default"]}報錯如下

報錯如下：

    Blocking waiting for file lock on package cache
    Updating git repository `https://github.com/suharev7/clickhouse-rs`
    Updating crates.io index
error: failed to select a version for `clickhouse-rs-cityhash-sys`.
    ... required by package `clickhouse-rs v1.0.0-alpha.1 (https://github.  com/suharev7/clickhouse-rs#ecf28f46)`
    ... which satisfies git dependency `clickhouse-rs` of package   `conflict v0.1.0 (/Users/jiashiwen/rustproject/conflict)`
versions that meet the requirements `^0.1.2` are: 0.1.2


the package `clickhouse-rs-cityhash-sys` links to the native library   `clickhouse-rs`, but it conflicts with a previous package which links to   `clickhouse-rs` as well:
package `clickhouse-rs-cityhash-sys v0.1.2`
    ... which satisfies dependency `clickhouse-rs-cityhash-sys = "^0.1.2"`   (locked to 0.1.2) of package `clickhouse v0.11.2 (https://github.com/  loyd/clickhouse.rs#4ba31e65)`
    ... which satisfies git dependency `clickhouse` (locked to 0.11.2) of   package `conflict v0.1.0 (/Users/jiashiwen/rustproject/conflict)`
Only one package in the dependency graph may specify the same links value.   This helps ensure that only one copy of a native library is linked in the   final binary. Try to adjust your dependencies so that only one package   uses the links ='clickhouse-rs-cityhash-sys' value. For more information,   see https://doc.rust-lang.org/cargo/reference/resolver.html#links.


failed to select a version for `clickhouse-rs-cityhash-sys` which could   resolve this conflict

錯誤描述還是很清楚的，clickhouse-rs-cityhash-sys 這個庫沖突了。仔細看了一下兩個庫的源碼，引用 clickhouse-rs-cityhash-sys 庫的方式是不一樣的。clickhouse.rs 是在其 Cargo.toml 文件中使用最普遍的方式引用的：

clickhouse-rs-cityhash-sys = { version = "0.1.2", optional = true }

clickhouse-rs 是通過本地方式引用的：

[dependencies.clickhouse-rs-cityhash-sys]
path = "clickhouse-rs-cityhash-sys"
version = "0.1.2"

clickhouse-rs-cityhash-sys 的源碼直接放在 clickhouse-rs 工程目錄下面。

一開始是有個直觀的想法，如果在一個工程中通過workspace 進行隔離，是不是會解決沖突問題呢？于是，工程的目錄結構從這樣：

.
├── Cargo.lock
├── Cargo.toml
└── src
    └── main.rs

改成了這樣

.
├── Cargo.lock
├── Cargo.toml
├── ck_http
│   ├── Cargo.toml
│   └── src
├── ck_tcp
│   ├── Cargo.toml
│   └── src
└── src
    └── main.rs

新建了兩個lib

cargo new ck_http --lib
cargo new ck_tcp --lib

在 workspace 中分別應用 clickhouse-rs 和 clickhouse.rs ,刪除根下 Cargo.toml 文件中的依賴關系。很可惜，workspace 沒有解決問題，報錯沒有一點兒差別。

又仔細看了看報錯，里面有這樣一段：

 the package `clickhouse-rs-cityhash-sys` links to the native library   `clickhouse-rs`, but it conflicts with a previous package which links to   `clickhouse-rs`

難道是 clickhouse-rs 這個名字沖突了？直接把clickhouse-rs源碼拉下來作為本地庫來試試呢？于是把 clickhouse-rs clone 到本地，稍稍修改一下ck_tcp workspace 的 Cargo.toml

clickhouse-rs = { path = "../../clickhouse-rs", features = ["default"]}

編譯后沖突依舊存在。翻翻clickhouse-rs/clickhouse-rs-cityhash-sys/Cargo.toml，里面的一個配置很可疑：

[package]
...
...
links = "clickhouse-rs"

把 links 隨便改個名字比如：links = "ck-rs-cityhash-sys"，編譯就通過了。

錯誤提示中這句話很重要：

Only one package in the dependency graph may specify the same links value.

看了一下 links 字段的含義

The links field
The links field specifies the name of a native library that is being linked to. More information can be found in the links section of the build script guide.

links 指定了本地包被鏈接的名字，在這里引起了沖突，改掉本地包中的名字自然解決了沖突，在依賴圖中保證唯一性很重要。

審核編輯：劉清