Add co-author trailers to merge commit.

When creating the merge commit for a batch, add a "Co-authored-by"
trailer to the commit message for each author contributing to the batch.

Fixes: #382

lib/github/github.ex

@@ -37,6 +37,18 @@ defmodule BorsNG.GitHub do
     GenServer.call(BorsNG.GitHub, {:get_pr, repo_conn, {pr_xref}})
   end
 
+  @spec get_pr_commits!(tconn, integer | bitstring) :: [BorsNG.GitHub.Commit.t]
+  def get_pr_commits!(repo_conn, pr_xref) do
+    {:ok, commits} = get_pr_commits(repo_conn, pr_xref)
+    commits
+  end
+
+  @spec get_pr_commits(tconn, integer | bitstring) ::
+    {:ok, [BorsNG.GitHub.Commit.t]} | {:error, term}
+  def get_pr_commits(repo_conn, pr_xref) do
+    GenServer.call(BorsNG.GitHub, {:get_pr_commits, repo_conn, {pr_xref}})
+  end
+
   @spec get_open_prs!(tconn) :: [tpr]
   def get_open_prs!(repo_conn) do
     {:ok, prs} = GenServer.call(

lib/github/github/commit.ex

@@ -0,0 +1,48 @@
+defmodule BorsNG.GitHub.Commit do
+  @moduledoc """
+  The structure of GitHub commit data.
+  """
+
+  defstruct sha: "", author_name: "", author_email: ""
+
+  @type tjson :: map
+
+  @type t :: %BorsNG.GitHub.Commit{
+    sha: bitstring,
+    author_name: bitstring,
+    author_email: bitstring,
+  }
+
+  @doc """
+  Convert from Poison-decoded JSON to a Commit struct.
+  """
+  @spec from_json!(tjson) :: t
+  def from_json!(json) do
+    {:ok, pr} = from_json(json)
+    pr
+  end
+
+  @doc """
+  Convert from Poison-decoded JSON to a Commit struct.
+  """
+  @spec from_json(tjson) :: {:ok, t} | :err
+  def from_json(%{
+    "sha" => sha,
+    "commit" => %{
+      "author" => %{
+        "name" => author_name,
+        "email" => author_email,
+      },
+    },
+  }) do
+    {:ok, %BorsNG.GitHub.Commit{
+      sha: sha,
+      author_name: author_name,
+      author_email: author_email,
+    }}
+  end
+
+  def from_json(x) do
+    {:error, x}
+  end
+end

lib/github/github/server.ex

@@ -82,6 +82,18 @@ defmodule BorsNG.GitHub.Server do
     end
   end
 
+  def do_handle_call(:get_pr_commits, repo_conn, {pr_xref}) do
+    case get!(repo_conn, "pulls/#{pr_xref}/commits") do
+      %{body: raw, status_code: 200} ->
+        commits = raw
+        |> Poison.decode!()
+        |> Enum.map(&BorsNG.GitHub.Commit.from_json!/1)
+        {:ok, commits}
+      e ->
+        {:error, :get_pr_commits, e.status_code, pr_xref}
+    end
+  end
+
   def do_handle_call(:get_open_prs, {{:raw, token}, repo_xref}, {}) do
     {:ok, get_open_prs_!(
       token,

lib/github/github/server_mock.ex

@@ -43,6 +43,13 @@ defmodule BorsNG.GitHub.ServerMock do
       ...>           id: 6,
       ...>           login: "bors-fanboi",
       ...>           avatar_url: "data:image/svg+xml,<svg></svg>"}}},
+      ...>     pr_commits: %{
+      ...>       1 => [
+      ...>         %GitHub.Commit{
+      ...>           sha: "00000001",
+      ...>           author_name: "Bors Fanboi",
+      ...>           author_email: "bors-fanboi@example.com"}
+      ...>       ] },
       ...>     statuses: %{},
       ...>     files: %{}}})
       iex> GitHub.get_open_prs!({{:installation, 91}, 14})
@@ -132,6 +139,16 @@ defmodule BorsNG.GitHub.ServerMock do
     end
   end
 
+  def do_handle_call(:get_pr_commits, repo_conn, {pr_xref}, state) do
+    with({:ok, repo} <- Map.fetch(state, repo_conn),
+         {:ok, pr_commits} <- Map.fetch(repo, :pr_commits),
+      do: Map.fetch(pr_commits, pr_xref))
+    |> case do
+      {:ok, _} = res -> {res, state}
+      _ -> {{:error, :get_pr_commits}, state}
+    end
+  end
+
   def do_handle_call(:get_installation_repos, installation_conn, {}, state) do
     with({:ok, installation} <- Map.fetch(state, installation_conn),
          {:ok, repos} <- Map.fetch(installation, :repos),

lib/worker/batcher.ex

@@ -292,7 +292,8 @@ defmodule BorsNG.Worker.Batcher do
         parents = [base.commit | Enum.map(patch_links, &(&1.patch.commit))]
         commit_message = Batcher.Message.generate_commit_message(
           patch_links,
-          toml.cut_body_after)
+          toml.cut_body_after,
+          gather_co_authors(batch, patch_links))
         head = GitHub.synthesize_commit!(
           repo_conn,
           %{
@@ -317,6 +318,15 @@ defmodule BorsNG.Worker.Batcher do
     {:conflict, nil}
   end
 
+  def gather_co_authors(batch, patch_links) do
+    repo_conn = get_repo_conn(batch.project)
+    patch_links
+    |> Enum.map(&(&1.patch.pr_xref))
+    |> Enum.flat_map(&GitHub.get_pr_commits!(repo_conn, &1))
+    |> Enum.map(&("#{&1.author_name} <#{&1.author_email}>"))
+    |> Enum.uniq
+  end
+
   defp setup_statuses(batch, toml) do
     toml.status
     |> Enum.map(&%Status{

lib/worker/batcher/message.ex

@@ -83,7 +83,7 @@ defmodule BorsNG.Worker.Batcher.Message do
     "#{acc}\n  * #{status_link}"
   end
 
-  def generate_commit_message(patch_links, cut_body_after) do
+  def generate_commit_message(patch_links, cut_body_after, co_authors) do
     commit_title = Enum.reduce(patch_links,
       "Merge", &"#{&2} \##{&1.patch.pr_xref}")
     commit_body = Enum.reduce(patch_links, "", fn link, acc ->
@@ -102,7 +102,10 @@ defmodule BorsNG.Worker.Batcher.Message do
       #{body}
       """
     end)
-    "#{commit_title}\n#{commit_body}"
+    co_author_trailers = co_authors
+    |> Enum.map(&("Co-authored-by: #{&1}"))
+    |> Enum.join("\n")
+    "#{commit_title}\n#{commit_body}\n#{co_author_trailers}\n"
   end
 
   def cut_body(nil, _), do: ""