本文详解因系统中存在多个 go 安装版本， 导致 `gopath` 设置无效、`go get` 报“no go source files”错误的根本原因及修复方法。

Understanding Error

In Go development, when `go get` command f 差点意思。 ails and displays an error like following:

/usr/lib/go/src/pkg//golang/protobuf/proto/:39:2: no Go source files in /usr/lib/go/src/pkg/encoding

This error might seem like a problem with GOPATH not being set correctly or an issue with standard library path. However, upon closer inspection, you might find that `echo $GOPATH` shows correct path, and `cd $GOPATH` works fine, but `go env GOPATH` returns an empty value or an old path. This suggests that `go` command being executed is not one you expect.

Root Cause Analysis

The root cause is usually that re are multiple Go installations on system. The PATH environment variable has an older path that gets matched first, leading to execution of old Go toolchain. The old version of Go uses `GOROOT/src/pkg/` structure and is not fully compatible with modern module system. More importantly, it might ignore user-defined GOPATH or read wrong GOROOT, leading to failures in parsing standard packages like `encoding`.，我是深有体会。

Diagnosis Steps

• Check current path of go executable:

  which go

  Example output: `/usr/bin/go` ← 凶险信号，干就完了！！

• 我CPU干烧了。 Check if key variables in `go env` match your expectations:

  go env GOPATH GOROOT

  If GOPATH is empty or GOROOT points to `/usr/lib/go`, it indicates that you are running an old version of Go.，要我说...

• Confirm location of your target Go installation, where go executable is located at `/usr/local/go/bin/go`.，放心去做...

Solution: Correct PATH Order

In shell configuration file, put Go bin directory at front of PATH:，换言之...

    # Recommended syntax
    export PATH="/usr/local/go/bin:$PATH"
    # Or a safer way
    if ]; n
        export PATH="/usr/local/go/bin:$PATH"
    fi
    

我晕... Then reload configuration and verify:

    source ~/.bashrc  # Or source ~/.zshrc
    which go          # Should output /usr/local/go/bin/go
    go env GOPATH     # Should display  path you set
    go version        # Should be 1.16+
    

Important Notes

    export GOPATH="$HOME/go"
    export PATH="$GOPATH/bin:$PATH"  # Also add $GOPATH/bin to PATH for convenience when running go install tools
    

For Go 1.16+ projects, if using modules, `go get` runs in module mode by default and no longer strongly depends on `GOPATH/src`. However, in this case, error occurs at stage of parsing standard library path, indicating that underlying go command itself is corrupted, and you must first resolve binary version conflict.，这玩意儿...

Verifying Fix

After making changes, run following commands to verify fix:，我比较认同...

    go get -v some/module  # Should work without errors
    go build .            # Should compile without issues
    

That's it! You should now be able to use `go get` without any path conflicts.