Another Dialyzer puzzle - 'Function will never be called'

Questions / Help
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1

I’m using the https://github.com/GoogleCloudPlatform/elixir-google-api/tree/master/clients/sheets project (a thin wrapper over the Google Sheets API) to create a Google sheet. The module that creates the sheets for us has a number of Dialyzer warnings but they are all the same root cause I’d imagine. The warning is “Function get_spreadsheet/1 will never be called” (where get_spreadsheet/1 is just an example).

Here’s the lead to that issue:

  defp create_google_sheet(nil) do
    Logger.info("No spreadsheet exists, creating one")
    month = @months[DateTime.utc_now().month]

    create_google_connection()
    |> Spreadsheets.sheets_spreadsheets_create(
      body: %{properties: %{title: "#{month}-#{DateTime.utc_now().year}-Deployment/Build Report"}}
    )
    |> get_spreadsheet()
end

The get_spreadsheet is just a shim to parse out the {:ok, response} or :error returned by sheets_spreadsheets_create. Here’s the one

  defp get_spreadsheet(result) do
    case result do
      {:ok, response} -> response
      {:error, _env} -> nil
    end
  end

Spreadsheets.sheets_spreadsheets_create spec is:

@spec sheets_spreadsheets_create(Tesla.Env.client, keyword()) :: {:ok, GoogleApi.Sheets.V4.Model.Spreadsheet.t} | {:error, Tesla.Env.t}

This functions fine. We’ve been running it in production for a month or so and it does exactly what we want but it bothers me that I don’t understand what dialyzer is trying to tell me. Any suggestions on what to look at?

2

“Function get_spreadsheet/1 will never be called” is just fallout from the real error. What does dialyzer say before that?

3

Dialyzed doesn’t see a valid way that create_google_sheet/1 will ever be called with nil argument therefore it assumes functions called from it will never be called.

At least that’s my assumption from what you have shown.

4

The first warning that Dialyzer outputs is related to that get_spreadsheet/1 call. it does not warn about the create_google_connection/0 or the Spreadsheets.sheets_spreadsheets_create function calls. If I make that get_spreadsheet function public it doesn’t change the warnings that dialyzer produces.

5

Can you provide a minified project that produces similar warnings?

Or is the original projects source publicly available?

6

thanks. Let me get that together. its a private project for my company but I can extract this issue. will post again when its available.

7

Here’s a public repo that demos the issue. https://github.com/fmcgeough/google_sheet_dialyer

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8

The PLT is building right now, I’ll take a look at it as my family gives me the time :wink:

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9

I’m kind of thinking it dies on the Spreadsheets.sheets_spreadsheets_create call from just an initial look?

EDIT: This is the dialyzer results if anyone is curious on that repo:

lib/google_spreadsheet.ex:22: Function deployments_sheet/0 has no local return
lib/google_spreadsheet.ex:34: Function create_google_sheet/1 has no local return
lib/google_spreadsheet.ex:55: Function get_spreadsheet/1 will never be called
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10

Its an upstream issue:

lib/google_api/sheets/v4/api/spreadsheets.ex:114: Function sheets_spreadsheets_create/1 has no local return
lib/google_api/sheets/v4/api/spreadsheets.ex:114: Function sheets_spreadsheets_create/2 has no local return

edit

I took the freedom to file an issue:

https://github.com/GoogleCloudPlatform/elixir-google-api/issues/73

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