Example: Refactor Go code using Comby

Our goal for this campaign is to simplify Go code by using Comby to rewrite statements of this form

fmt.Sprintf("%d", arg)

to this form:


The semantics are the same, but one more cleanly expresses the intention behind the code.

We’re going to use two Docker containers in our action.

The first container launches Comby to rewrite the Go code.

The second container runs goimports to update the import statements in the updated Go code so that strconv is correctly imported and, possibly, fmt is removed.

Here is the action.json file that defines this as an action:

  "scopeQuery": "lang:go fmt.Sprintf",
  "steps": [
      "type": "docker",
      "image": "comby/comby",
      "args": ["-in-place", "fmt.Sprintf(\"%d\", :[v])", "strconv.Itoa(:[v])", "-matcher", ".go", "-d", "/work"]
      "type": "docker",
      "image": "cytopia/goimports",
      "args": ["-w", "/work"]

Please note that the "scopeQuery" makes sure that the repositories over which we run the action all contain Go code in which we have a call to fmt.Sprintf. That narrows the list of repositories down considerably, even though we still need to search through the whole repository with Comby. (We’re aware that this is a limitation and are working on improving the workflows involving exact search results.)

Save the definition in a file, for example go-comby.action.json.

Now we can execute the action and turn it into a campaign:

  1. Make sure that the "scopeQuery" returns the repositories we want to run over:

    src actions scope-query -f go-comby.action.json
  2. Execute the action and create a patchset:

    src actions exec -f action.json | src campaign patchset create-from-patches
  3. Follow the printed instructions to create the campaign on Sourcegraph.