Go Modules - Part 1

-   Go 1.13及以后版本GO111MODULE=auto的行为变化。
    
    GO111MODULE的默认值依然为auto。但无论repo是否在GOPATH，只要目录有go.mod，go编译器都会使用go module来管理依赖

-   如何创建模块

    新建工作区和项目文件夹
    ```
    $ mkdir -p $HOME/Desktop/go/hello
    $ cd $HOME/Desktop/go/hello
    $
    ```

    init mod init $path  
    一是作为模块标识，二是作为模块的import path 
    此时会生成go.mod文件
    当其他项目引用这个模块下的 package 时都会以该 import $path 作为共同的前缀  
    ```
    $ go mod init example.com/hello
    go: creating new go.mod: module example.com/hello
    $ cat go.mod
    module example.com/hello

    go 1.15
    $
    ```

    新建go文件`hello.go`
    ```
    package hello

    func Hello() string {
        return "Hello, world."
    }
    ```

    新建测试文件`hello_test.go`，测试是否能正常调用Hello方法
    ```
    package hello

    import "testing"

    func TestHello(t *testing.T) {
        want := "Hello, world."
        if got := Hello(); got != want {
            t.Errorf("Hello() = %q, want %q", got, want)
        }
    }
    ```

    运行测试文件
    ```
    $ go test
    PASS
    ok      example.com/hello       1.221s
    $
    ```

-   如何添加依赖项

    修改hello.go。用rsc.io/quote来实现Hello
    ```
    package hello

    import "rsc.io/quote"

    func Hello() string {
        return quote.Hello()
    }
    ```

    再次运行测试。看来Hello()方法实现了国际化功能，需要修改一下测试用例。
    ```
    ...
    func TestHello(t *testing.T) {
        want := "你好，世界。"
        if got := Hello(); got != want {
            t.Errorf("Hello() = %q, want %q", got, want)
        }
    }
    ```

    测试通过了，证明Hello功能正常
    ```
    $ go test
    PASS
    ok      example.com/hello       0.377s
    $
    ```

    此时会把直接依赖写到go.mod中
    ```
    $ cat go.mod
    module example.com/hello

    go 1.15

    require rsc.io/quote v1.5.2
    $
    ```

    尝试列出目前的所有依赖。当前模块(主模块)始终是第一行，随后的才是真正的依赖关系
    ```
    $ go list -m all
    example.com/hello
    golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c
    rsc.io/quote v1.5.2
    rsc.io/sampler v1.3.0
    ```

    尝试列出所有的依赖关系。清晰明了，这个功能大赞
    ```
    $ go mod graph
    example.com/hello rsc.io/quote@v1.5.2
    rsc.io/quote@v1.5.2 rsc.io/sampler@v1.3.0
    rsc.io/sampler@v1.3.0 golang.org/x/text@v0.0.0-20170915032832-14c0d48ead0c
    ```

    所有真正的依赖和哈希值会记录到go.sum中。哈希值的作用是确保所有依赖项不会被恶意修改。
    ```
    $ cat go.sum
    golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c h1:qgOY6WgZOaTkIIMiVjBQcw93ERBE4m30iBm00nkL0i8=
    golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
    rsc.io/quote v1.5.2 h1:w5fcysjrx7yqtD/aO+QwRjYZOKnaM9Uh2b40tElTs3Y=
    rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPXsUe+TKr0=
    rsc.io/sampler v1.3.0 h1:7uVkIFmeBqHfdjD+gZwtXXI+RODJ2Wc4O7MPEh/QiW4=
    rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
    ```

-   如何更新依赖项。版本号最好带着语义信息，v0.1.2。主要版本是0，次要版本是1，补丁版本是2

    尝试升级一下golang.org/x/text
    ```
    $ go get golang.org/x/text
    go: golang.org/x/text upgrade => v0.3.3
    go: downloading golang.org/x/text v0.3.3
    $
    ```

    执行go list -m all并且看看go.mod和go.sum情况。  
    golang.org/x/text已经升级到v0.3.3版本，go.mod也改成了`golang.org/x/text v0.3.3 // indirect`。  
    `indirect`表示该依赖不是由当前项目直接依赖，而是由其他依赖包间接依赖的。  
    ```
    $ go list -m all
    example.com/hello
    golang.org/x/text v0.3.3
    golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e
    rsc.io/quote v1.5.2
    rsc.io/sampler v1.3.0
    $ cat go.mod
    module example.com/hello

    go 1.15

    require (
            golang.org/x/text v0.3.3 // indirect
            rsc.io/quote v1.5.2
    )
    $ cat go.sum
    golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c h1:qgOY6WgZOaTkIIMiVjBQcw93ERBE4m30iBm00nkL0i8=
    golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
    golang.org/x/text v0.3.3 h1:cokOdA+Jmi5PJGXLlLllQSgYigAEfHXJAERHVMaCc2k=
    golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
    golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
    rsc.io/quote v1.5.2 h1:w5fcysjrx7yqtD/aO+QwRjYZOKnaM9Uh2b40tElTs3Y=
    rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPXsUe+TKr0=
    rsc.io/sampler v1.3.0 h1:7uVkIFmeBqHfdjD+gZwtXXI+RODJ2Wc4O7MPEh/QiW4=
    rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
    ```

    尝试升级rsc.io/sampler。发现版本太先进，兼容不了旧版本
    ```
    $ go get rsc.io/sampler
    go: rsc.io/sampler upgrade => v1.99.99
    go: downloading rsc.io/sampler v1.99.99
    $ go test
    --- FAIL: TestHello (0.00s)
    hello_test.go:8: Hello() = "99 bottles of beer on the wall, 99 bottles of beer, ...", want "Hello, world."
    FAIL
    exit status 1
    FAIL	example.com/hello	0.014s
    $
    ```

    尝试列出可用的版本以及挑选一个补丁版本。go get默认是获取@latest版本
    ```
    $ go list -m -versions rsc.io/sampler    
    rsc.io/sampler v1.0.0 v1.2.0 v1.2.1 v1.3.0 v1.3.1 v1.99.99
    $ go get rsc.io/sampler@v1.3.1
    ```

    此时。$GOPATH/pkg/mod/rsc.io存在rsc.io/sampler的多个版本
    ```
    $ cd $HOME/go/pkg/mod/rsc.io
    $ ls
    quote@v1.5.2     sampler@v1.3.0   sampler@v1.3.1   sampler@v1.99.99
    $
    ```

-   如何引用同一个依赖的不同主版本

    修改hello.go。引用rsc.io/quote/v3
    ```
    package hello

    import (
        "rsc.io/quote"
        quoteV3 "rsc.io/quote/v3"
    )

    func Hello() string {
        return quote.Hello()
    }

    func Proverb() string {
        return quoteV3.Concurrency()
    }
    ```

    给测试文件添加以下行
    ```
    ...
    func TestProverb(t *testing.T) {
        want := "Concurrency is not parallelism."
        if got := Proverb(); got != want {
            t.Errorf("Proverb() = %q, want %q", got, want)
        }
    }
    ```

    再次测试一下
    ```
    $ go test
    PASS
    ok      example.com/hello       0.377s
    $
    ```

    此时项目同时依赖rsc.io/quote和rsc.io/quote/v3
    ```
    $ go list -m rsc.io/q... 
    rsc.io/quote v1.5.2
    rsc.io/quote/v3 v3.1.0
    ```

    总结:
    -   主要版本不相同时要发布不同的模块，模块必须以版本号结尾
    -   相同主要版本之间要兼容
    -   像rsc.io/quote如果有多个主要版本。需要发布rsc.io/quote，rsc.io/quote/v2和rsc.io/quote/v3等模块

-   引用同一个依赖的不同版本毕竟不是什么好事。尝试将旧的api升级到新的api，然后将旧的依赖删除。

    查看rsc.io/quote/v3版本有什么api。像是Hello升级到了HelloV3
    ```
    $ go doc rsc.io/quote/v3
    package quote // import "rsc.io/quote/v3"

    Package quote collects pithy sayings.

    func Concurrency() string
    func GlassV3() string
    func GoV3() string
    func HelloV3() string
    func OptV3() string
    $ 
    ```

    修改hello.go，更换一下api
    ```
    package hello

    import quoteV3 "rsc.io/quote/v3"

    func Hello() string {
        return quoteV3.HelloV3()
    }

    func Proverb() string {
        return quoteV3.Concurrency()
    }
    ```

    既然没有了多个版本，可以不用alias
    ```
    package hello

    import "rsc.io/quote/v3"

    func Hello() string {
        return quote.HelloV3()
    }

    func Proverb() string {
        return quote.Concurrency()
    }
    ```

    重新运行test。一切正常
    ```
    $ go test 
    PASS
    ok      example.com/hello       1.626s
    ```

-   如何删除已下载但未引用的依赖。例如`rsc.io/quote`

    ```
    $ go list -m all
    example.com/hello
    golang.org/x/text v0.3.3
    golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e
    rsc.io/quote v1.5.2
    rsc.io/quote/v3 v3.1.0
    rsc.io/sampler v1.3.1
    
    $ cat go.mod
    module example.com/hello

    go 1.15

    require (
            golang.org/x/text v0.3.3 // indirect
            rsc.io/quote v1.5.2
            rsc.io/quote/v3 v3.1.0
            rsc.io/sampler v1.3.1 // indirect
    )
    ```
    
    利用tidy命令删除未使用的依赖项
    ```
    $ go mod tidy
    $ go list -m all
    example.com/hello
    golang.org/x/text v0.3.3
    golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e
    rsc.io/quote/v3 v3.1.0
    rsc.io/sampler v1.3.1
    $ cat go.mod
    module example.com/hello

    go 1.15

    require (
            golang.org/x/text v0.3.3 // indirect
            rsc.io/quote/v3 v3.1.0
            rsc.io/sampler v1.3.1 // indirect
    )
    ```

    重新测试
    ```
    $ go test
    PASS
    ok      example.com/hello       3.088s
    ```


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Go Modules - Part 1 #5

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Go Modules - Part 1 #5

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