查看编译文件

我们用go list来查看在当前平台下 os/exec包里有哪些文件将会被编译

看当前项目下，有哪些文件会被编译，命令如下：

这里的 {{.GoFiles}} 是text/template里的模板代码

go list 命令的信息如下：
查看包名、路径、依赖项等等信息。
参数:
-json: 使用 json 格式输出包的相关信息，包括下面的依赖和导⼊。
-f{{.Deps}}: 查看依赖包，包括直接或间接依赖。
-f{{.Imports}}: 查看导入的包。

D:mycodesgolangsrcitbucket.orgkardianososext>go list -f
flag needs an argument: -f
usage: list [-e] [-f format] [-json] [build flags] [packages]

List lists the packages named by the import paths, one per line.

The default output shows the package import path:

    code.google.com/p/google-api-go-client/books/v1
    code.google.com/p/goauth2/oauth
    code.google.com/p/sqlite

The -f flag specifies an alternate format for the list, using the
syntax of package template. The default output is equivalent to -f
'{{.ImportPath}}'. The struct being passed to the template is:

    type Package struct {
        Dir           string // directory containing package sources
        ImportPath    string // import path of package in dir
        ImportComment string // path in import comment on package statement
        Name          string // package name
        Doc           string // package documentation string
        Target        string // install path
        Goroot        bool   // is this package in the Go root?
        Standard      bool   // is this package part of the standard Go library?

Stale bool // would 'go install' do anything for this package?

Root string // Go root or Go path dir containing this package

        // Source files
        GoFiles        []string // .go source files (excluding CgoFiles, TestGoF
iles, XTestGoFiles)
        CgoFiles       []string // .go sources files that import "C"
        IgnoredGoFiles []string // .go sources ignored due to build constraints
        CFiles         []string // .c source files
        CXXFiles       []string // .cc, .cxx and .cpp source files
        MFiles         []string // .m source files
        HFiles         []string // .h, .hh, .hpp and .hxx source files
        SFiles         []string // .s source files
        SwigFiles      []string // .swig files
        SwigCXXFiles   []string // .swigcxx files
        SysoFiles      []string // .syso object files to add to archive

        // Cgo directives
        CgoCFLAGS    []string // cgo: flags for C compiler
        CgoCPPFLAGS []string // cgo: flags for C preprocessor
        CgoCXXFLAGS []string // cgo: flags for C++ compiler
        CgoLDFLAGS   []string // cgo: flags for linker
        CgoPkgConfig []string // cgo: pkg-config names

        // Dependency information
        Imports []string // import paths used by this package
        Deps    []string // all (recursively) imported dependencies

        // Error information
        Incomplete bool            // this package or a dependency has an error
        Error      *PackageError   // error loading package
        DepsErrors []*PackageError // errors loading dependencies

        TestGoFiles []string // _test.go files in package
        TestImports []string // imports from TestGoFiles
        XTestGoFiles []string // _test.go files outside package
        XTestImports []string // imports from XTestGoFiles
    }

The template function "join" calls strings.Join.

The template function "context" returns the build context, defined as:

        type Context struct {
                GOARCH        string   // target architecture
                GOOS          string   // target operating system
                GOROOT        string   // Go root
                GOPATH        string   // Go path
                CgoEnabled    bool     // whether cgo can be used
                UseAllFiles   bool     // use files regardless of +build lines,
file names
                Compiler      string   // compiler to assume when computing targ
et paths
                BuildTags     []string // build constraints to match in +build l
ines
                ReleaseTags   []string // releases the current release is compat
ible with
                InstallSuffix string   // suffix to use in the name of the insta
ll dir
        }

For more information about the meaning of these fields see the documentation
for the go/build package's Context type.

The -json flag causes the package data to be printed in JSON format
instead of using the template format.

The -e flag changes the handling of erroneous packages, those that
cannot be found or are malformed. By default, the list command
prints an error to standard error for each erroneous package and
omits the packages from consideration during the usual printing.
With the -e flag, the list command never prints errors to standard
error and instead processes the erroneous packages with the usual
printing. Erroneous packages will have a non-empty ImportPath and
a non-nil Error field; other information may or may not be missing
(zeroed).

For more about build flags, see 'go help build'.

For more about specifying packages, see 'go help packages'.

编译标签

在源代码里添加标注，通常称之为编译标签( build tag) ，编译标签是在尽量靠近源代码文件顶部的地方用注释的方式添加
go build在构建一个包的时候会读取这个包里的每个源文件并且分析编译便签，这些标签决定了这个源文件是否参与本次编译

编译标签添加的规则（附上原文）：

a build tag is evaluated as the OR of space-separated options
each option evaluates as the AND of its comma-separated terms
each term is an alphanumeric word or, preceded by !, its negation

编译标签由空格分隔的编译选项(options)以"或"的逻辑关系组成
每个编译选项由逗号分隔的条件项以逻辑"与"的关系组成
每个条件项的名字用字母+数字表示，在前面加!表示否定的意思

比如 https://bitbucket.org/kardianos/osext/src 这里的 osext_procfs.go 文件头上的 +build 部分就是。

这里标示 linux netbsd openbsd solaris 这些操作系统下会编译这个文件。

更复杂的编译标签可以参考： http://blog.csdn.net/varding/article/details/12675971

文件后缀

这个方法通过改变文件名的后缀来提供条件编译，这种方案比编译标签要简单，go/build可以在不读取源文件的情况下就可以决定哪些文件不需要参与编译

文件命名约定可以在go/build 包里找到详细的说明，简单来说如果你的源文件包含后缀：_$GOOS.go，那么这个源文件只会在这个平台下编译，_$GOARCH.go也是如此。这两个后缀可以结合在一起使用，但是要注意顺序：_$GOOS_$GOARCH.go，不能反过来用：_$GOARCH_$GOOS.go

比如 https://bitbucket.org/kardianos/osext/src 这里的文件就是这个规则

osext_plan9.go 只会在 plan9 中编译。

osext_windows.go 只会在windows下编译。

参考资料：

使用go build 进行条件编译
http://blog.csdn.net/varding/article/details/12675971