Tip: renaming Go modules

I’ve been working on some experimental code lately, and part of the experiment has been where and how to host it. Because Go modules use the hosting location as the import path, this means i’ve been renaming my modules quite a bit.

manual renames

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There are essentially two steps to renaming a module.

1. Change how the module defines its own name (in go.mod)
2. Change inter-module imports to use this new name

The first step involves editing go.mod and changing the module directive. You could do this with your editor, but Go provides a simpler way:

go mod edit -module ${newmodulename}

This command will update the module directive in the current module.

Next up, we need to update all of our imports. This one does not have a handy go-specific tool, but it is essentially a global search-and-replace. sed is a classic tool for this type of work.

find . -name '*.go' | xargs sed -i ''  -e "s^${oldmodule}^${newmodule}^g"

This is finding all go files, and passing them to sed.

• -i '' says edit each file independently, and don’t make backup files.
• the s substitution uses carets (^) because the traditional separator (/) is common in go module names, and an alternate separator lets us avoid heavily escaping our module paths. sed works with a variety of separators.

This two-step process is fairly straightforward, but involves a bunch of tedious fill-in-the-blanks work. You could write a script to do this, but I chose a different path.

taskfile

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For small automation tasks, I like to use taskfile.dev – its a bit like make but with yaml syntax and a lot less baggage. Here’s how I structured my task for renaming Go modules:

  go:modrename:
    desc: "rename the current go module"
    dir: "{{.USER_WORKING_DIR}}"
    env:
      oldmodule:
        sh: go mod edit -json | jq -r '.Module.Path'
    cmds:
      # First, show an error if the required arg is missing.
      - '{{if .CLI_ARGS}}true{{else}}echo "must specify new module path."; false{{end}}'
      - go mod edit -module {{.CLI_ARGS}}
      - find . -name '*.go' | echo xargs sed -i \'\'  -e "s^${oldmodule}^{{.CLI_ARGS}}^g"

I’m using a global Taskfile.yaml, in my home directory, so I can run this command from anywhere like this:

task -g go:modrename -- github.com/mynew/modulepath

(the -g tells Task to look in my home directory for the global task file, rather than the current directory).

This gives me a quick, repeatable way to rename modules, making it easier for me to use a forked module. And helps me to rename it back before I send a PR (hopefully)!