Go language file naming convention: special processing of files starting with an underscore or dot

The go build command of the Go language ignores source files whose file names begin with an underscore or dot. This behavior is defined by the standard library go/build package and is intended to exclude temporary or editor-related files. Therefore, developers should avoid using such naming methods to define the valid source code of the package, otherwise the functions and types defined in it will not be imported and used, affecting the normal construction and operation of the program.

File identification mechanism for Go build tools

In the development practice of Go language, file names usually follow certain conventions. However, the go build command will take a special treatment for Go source files whose file names begin with an underscore (_) or a period (.): they will be completely ignored and will not participate in compilation as a valid part of the package. This means that even if exported functions or types are defined in these files, they cannot be accessed by other files within the same package or by other code that imports the package.

This behavior is not an arbitrary decision of the go toolchain, but is clearly defined by the go/build package in the Go standard library. The go/build package is responsible for parsing the structure and dependencies of Go packages. Its internal logic clearly states that when scanning a package directory, the following types of files will be excluded:

• .go files in the package documentation.
• Files whose file names begin with _ or . (generally considered editor temporary files or auxiliary files that should not participate in the build).
• Files that do not meet the build constraints of the current build environment (e.g. operating system, architecture, etc.).

The original intention of this design choice is to facilitate developers to manage auxiliary files in the project, such as:

• Temporary files generated by the editor (such as _temp.go, .vscode.go).
• Draft files or configure scripts that the user wishes to exclude from the build process.

Practical impact and examples

When a Go package contains source files starting with an underscore or dot, their contents will not be compiled into the final executable or library. For example, consider the following project structure:

 mypkg/
  _internal_helper.go // This file will be ignored by go build .config_data.go // This file will also be ignored by go build api.go // This file will be included in the build utils.go // This file will be included in the build

If a function InternalFunc() is defined in _internal_helper.go, then trying to call mypkg.InternalFunc() in api.go or utils.go will result in a compilation error because the compiler cannot find the function.

Distinguish special purpose documents

It should be noted that there are some file name conventions in the Go language that also contain underscores, but they are handled differently from the above, for example:

• Test file (_test.go) : such as my_package_test.go. Such files will be compiled and run when executing the go test command, but will be ignored in the regular go build command. The underscore here is not the first character of the file name.
• Build constraint files (_os.go, _arch.go) : such as network_unix.go or data_windows.go. Such files are included in the build in certain environments and ignored in others, depending on the operating system or architecture their suffix matches. Likewise, the underscore here is not the first character of the file name.

The core difference is that the go build command only ignores Go source files whose file names begin with an underscore or a period. For the case where an underscore appears in the middle of a file name, the Go compiler will handle it according to its specific semantics (such as test files, build constraints).

Things to note

1. Avoid for core code : The core logic of a package or any code expected to be compiled and used should never be placed in a Go source file that starts with an underscore or dot.
2. Make good use of the exclusion mechanism : If you really need to exclude certain Go files from the build, such as as drafts, temporary scripts, or auxiliary files for specific development tools, using _ or . as a prefix is ​​an effective and Go-compliant approach.
3. Understand build constraints : Distinguish between hard exclusion rules for underscores/dots at the beginning of file names and conditional inclusion/exclusion rules based on specific semantics such as _test.go and _os.go.

Summarize

The go build command of the Go language adopts an explicit ignore policy for Go source files whose file names begin with an underscore or dot. This is designed to simplify project management and exclude temporary files or non-build code. As a Go developer, it is crucial to understand and follow this file naming convention to ensure that your code compiles, packages, and runs correctly and avoids potential problems caused by unrecognized files.

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