Why Does 'Replacement Module Without Version Must Be Directory Path' Error Occur in Go Modules?

Go Modules and the Elusiveness of Replacements

In the realm of Go modules, the replace directive holds the promise of substituting a locally developed package for a remote one, enabling you to work with your own code while experimenting or troubleshooting. However, as you have experienced, replacing a package without a specified version can prove to be a vexing endeavor.

The error message you encountered, "replacement module without version must be directory path (rooted or starting with .)," highlights the crucial requirement that the path provided to the replace directive must be absolute or relative to the module's root.

Overcoming the Path Perplexity

The path conundrum arises from the way Go modules are structured. The go.mod file serves as the centerpiece, establishing the module's identity and its dependencies. Packages that reside within the same module as the go.mod file can be referenced directly, without the need for replacements. However, when dealing with packages external to the module, the replace directive comes into play.

In your case, you aimed to utilize a local package named mypack. To achieve this, you specified the following replace directive in your go.mod file:

replace mypack -> ./src/mypack

Unfortunately, this path is neither absolute nor relative to the module's root. The "./" prefix signifies a path relative to the current working directory, which is not the same as the module's root.

Establishing a Path to Harmony

To rectify this issue, follow these steps:

1. Convert mypack into a go module: Create a go.mod file within the mypack folder. This will establish mypack as an independent module.
2. Specify an absolute path or a path relative to the module's root: In your go.mod file, modify the replace directive to use an absolute or relative path to mypack. For example, if mypack is a sibling of your module's root, you could use:

replace mypack -> ../mypack

Additional Considerations

Remember that the replace directive is intended for temporary local overrides. If you want to make a permanent substitution, consider using a vendoring tool or explicitly vendoring mypack into your module.

Related Resource:

• How to use a module that is outside of "GOPATH" in another module?

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