Allow {:from_app, app_name} as a version for releases (#9280)

Sometimes it is desireable to lookup the version from another
application to use as the version for a release. This is true in the
case of umbrella applications, where a particular app may be targetted
for a release.

Using `{:from_app, :my_app}` will allow the version returned from
`Application.spec(:my_app, :vsn)` to be used as the version.

Author: Gazler

lib/mix/lib/mix/release.ex

@@ -7,7 +7,8 @@ defmodule Mix.Release do
   The Mix.Release struct has the following read-only fields:
 
     * `:name` - the name of the release as an atom
-    * `:version` - the version of the release as a string
+    * `:version` - the version of the release as a string or
+       `{:from_app, app_name}
     * `:path` - the path to the release root
     * `:version_path` - the path to the release version inside the release
     * `:applications` - a map of application with their definitions
@@ -47,7 +48,7 @@ defmodule Mix.Release do
           name: atom(),
           version: String.t(),
           path: String.t(),
-          version_path: String.t(),
+          version_path: String.t() | {:from_app, application()},
           applications: %{application() => keyword()},
           boot_scripts: %{atom() => [{application(), mode()}]},
           erts_version: charlist(),
@@ -112,6 +113,24 @@ defmodule Mix.Release do
           )
       end)
 
+    version =
+      case version do
+        {:from_app, app} ->
+          Application.load(app)
+          version = Application.spec(app, :vsn)
+
+          if !version do
+            Mix.raise(
+              "Could not find version for #{inspect(app)}, please make sure the application exists"
+            )
+          end
+
+          to_string(version)
+
+        _ ->
+          version
+      end
+
     {config_providers, opts} = Keyword.pop(opts, :config_providers, [])
     {steps, opts} = Keyword.pop(opts, :steps, [:assemble])
     validate_steps!(steps)

lib/mix/lib/mix/tasks/release.ex

@@ -386,8 +386,10 @@ defmodule Mix.Tasks.Release do
     * `:path` - the path the release should be installed to.
       Defaults to `"_build/MIX_ENV/rel/RELEASE_NAME"`.
 
-    * `:version` - the release version as a string. Defaults to the current
-      application version.
+    * `:version` - the release version as a string or `{:from_app, app_name}`.
+      Defaults to the current application version. The `{:from_app, app_name}` format
+      can be used to easily reference the application version from another application.
+      This is particularly useful in umbrella applications.
 
     * `:quiet` - a boolean that controls if releases should write to the standard
       output its steps. Defaults to `false`.

lib/mix/test/mix/release_test.exs

@@ -50,6 +50,21 @@ defmodule Mix.ReleaseTest do
       assert release.options[:quiet]
     end
 
+    test "allows specifying the version from an application" do
+      overrides = [version: {:from_app, :elixir}]
+      release = from_config!(nil, config(), overrides)
+
+      assert release.version == to_string(Application.spec(:elixir, :vsn))
+    end
+
+    test "raises when :from_app is used with an app that doesn't exist" do
+      overrides = [version: {:from_app, :not_valid}]
+
+      assert_raise Mix.Error,
+                   ~r"Could not find version for :not_valid, please make sure the application exists",
+                   fn -> from_config!(nil, config(), overrides) end
+    end
+
     test "includes applications" do
       release = from_config!(nil, config(), [])
       assert release.applications.mix[:path] == to_charlist(Application.app_dir(:mix))