mix.exs: Do not bail out when .git doesn’t exists

mix.exs

@@ -203,19 +203,26 @@ defmodule Pleroma.Mixfile do
     identifier_filter = ~r/[^0-9a-z\-]+/i
 
     # Pre-release version, denoted from patch version with a hyphen
+    {tag, tag_err} =
+      System.cmd("git", ["describe", "--tags", "--abbrev=0"], stderr_to_stdout: true)
+
+    {describe, describe_err} = System.cmd("git", ["describe", "--tags", "--abbrev=8"])
+    {commit_hash, commit_hash_err} = System.cmd("git", ["rev-parse", "--short", "HEAD"])
+
     git_pre_release =
-      with {tag, 0} <-
-             System.cmd("git", ["describe", "--tags", "--abbrev=0"], stderr_to_stdout: true),
-           {describe, 0} <- System.cmd("git", ["describe", "--tags", "--abbrev=8"]) do
-        describe
-        |> String.trim()
-        |> String.replace(String.trim(tag), "")
-        |> String.trim_leading("-")
-        |> String.trim()
-      else
-        _ ->
-          {commit_hash, 0} = System.cmd("git", ["rev-parse", "--short", "HEAD"])
+      cond do
+        tag_err == 0 and describe_err == 0 ->
+          describe
+          |> String.trim()
+          |> String.replace(String.trim(tag), "")
+          |> String.trim_leading("-")
+          |> String.trim()
+
+        commit_hash_err == 0 ->
           "0-g" <> String.trim(commit_hash)
+
+        true ->
+          ""
       end
 
     # Branch name as pre-release version component, denoted with a dot
@@ -233,6 +240,8 @@ defmodule Pleroma.Mixfile do
           |> String.replace(identifier_filter, "-")
 
         branch_name
+      else
+        _ -> "stable"
       end
 
     build_name =