Synopsis Of The Error

I encountered this error while learning how to call the code in an external package.
While following the tutorial, I ran the following code:

package main

import (
    "fmt"
    "rsc.io/quote"
)

func main() {
    fmt.Println(quote.Go())
}

I got the following unexpected output after running the go run . command:

package rsc.io/quote
    imports rsc.io/quote: import cycle not allowed

Upon running the go build command, I got the following output:

package command-line-arguments
    imports rsc.io/quote
    imports rsc.io/quote: import cycle not allowed

How I Fixed The Error

First and foremost, no error message is a personal attack on your abilities as a developer.

Upon doing my research I learned that for the source code to compile, the go.mod file MUST exist. This means that you have to initialize your module using the go mod init hello command and the output for doing that is:

go: creating new go.mod: module hello
go: to add module requirements and sums:
        go mod tidy

After initializing the module, run the go mod tidy command.

Alternatively, you can run the go mod tidy command as stipulated in the documentation.

What Does The go mod tidy Command Do?

The go mod tidy command matches the go.mod file with the dependencies required in the source files. To do this:

• It downloads all the dependencies that are required in your source files and updates the go.mod file with the dependencies.

• It removes all dependencies from the go.mod file which are not required in the source files.

In this case, it downloads the rsc.io/quote package and a go.sum file for authenticating the module.

Conclusion

Once you run your code using the go build command, you'll get the expected output, i.e:

Don't communicate by sharing memory, share memory by communicating.

Reference

1. https://stackoverflow.com/a/64442305/18533523

2. https://go.dev/doc/tutorial/getting-started

3. https://go.dev/ref/mod#authenticating

4. https://golangbyexample.com/go-mod-tidy/