Add override_for to dep options

lib/mix/lib/mix/dep.ex

@@ -392,7 +392,7 @@ defmodule Mix.Dep do
     if dep.opts[:from_umbrella] || other.opts[:from_umbrella] do
       "Please remove the conflicting options from your definition"
     else
-      "Ensure they match or specify one of the above in your deps and set \"override: true\""
+      "Ensure they match or specify one of the above in your deps and set \"override: true\" or \"override_for:\""
     end
   end
 

lib/mix/lib/mix/dep/converger.ex

@@ -299,7 +299,7 @@ defmodule Mix.Dep.Converger do
         end
 
         cond do
-          in_upper? && other_opts[:override] ->
+          in_upper? && (other_opts[:override] || override_for?(other_opts, app)) ->
             {:match, list}
 
           not converge?(other, dep) ->
@@ -331,6 +331,10 @@ defmodule Mix.Dep.Converger do
     end
   end
 
+  defp override_for?(opts, app) do
+    !!opts[:override_for] && app in opts[:override_for]
+  end
+
   defp with_matching_only_and_targets(other, dep, in_upper?) do
     %{opts: opts} = dep
 

lib/mix/lib/mix/dep/fetcher.ex

@@ -110,6 +110,8 @@ defmodule Mix.Dep.Fetcher do
     Mix.Dep.Lock.write(lock, opts)
     mark_as_fetched(parent_deps)
 
+    evaluate_overrides(Enum.filter(deps, & &1.opts[:override_for]), deps)
+
     # See if any of the deps diverged and abort.
     show_diverged!(Enum.filter(all_deps, &Mix.Dep.diverged?/1))
 
@@ -156,6 +158,43 @@ defmodule Mix.Dep.Fetcher do
     end)
   end
 
+  defp evaluate_overrides([], _deps), do: :ok
+
+  defp evaluate_overrides(override_deps, deps) do
+    for override_dep <- override_deps,
+        dep <- deps,
+        dep_dependency <- dep.deps,
+        override_dep.app == dep_dependency.app do
+      overridden? = dep.app in override_dep.opts[:override_for]
+
+      {:ok, satisfied?} =
+        Mix.Dep.Loader.vsn_match(dep_dependency.requirement, override_dep.requirement, dep.app)
+
+      cond do
+        overridden? && satisfied? ->
+          show_expired_override(override_dep, dep.app)
+
+        not overridden? && not satisfied? ->
+          show_missing_override(override_dep, dep.app)
+
+        true ->
+          :ok
+      end
+    end
+
+    :ok
+  end
+
+  defp show_expired_override(dep, app) do
+    Mix.shell().info(
+      "Dependency #{Mix.Dep.format_dep(dep)} no longer requires override_for on #{app}"
+    )
+  end
+
+  defp show_missing_override(dep, app) do
+    Mix.shell().info("Dependency #{Mix.Dep.format_dep(dep)} requires override_for on #{app}")
+  end
+
   defp show_diverged!([]), do: :ok
 
   defp show_diverged!(deps) do

lib/mix/lib/mix/tasks/deps.ex

@@ -97,6 +97,13 @@ defmodule Mix.Tasks.Deps do
     * `:override` - if set to `true` the dependency will override any other
       definitions of itself by other dependencies
 
+    * `:override_for` - if set to a list of applications requiring the
+      override (see the `override` opt), warnings will be emitted when other
+      apps are added that also require an override, and when the override is no
+      longer required. This setting behaves similarly to `override: true` for
+      dependency resolution. It does not fail resolution when more apps require
+      an override.
+
     * `:manager` - Mix can also compile Rebar3 and makefile projects
       and can fetch sub dependencies of Rebar3 projects. Mix will
       try to infer the type of project but it can be overridden with this

lib/mix/test/mix/dep_test.exs

@@ -1240,6 +1240,47 @@ defmodule Mix.DepTest do
     end
   end
 
+  describe "override_for" do
+    test "warns when overrides are no longer needed for an app" do
+      deps = [
+        {:deps_repo, "0.1.0", path: "custom/deps_repo"},
+        {:git_repo, "0.1.0",
+         git: MixTest.Case.fixture_path("git_repo"), override_for: [:deps_repo]}
+      ]
+
+      with_deps(deps, fn ->
+        in_fixture("deps_status", fn ->
+          Mix.Tasks.Deps.Get.run([])
+          Mix.Tasks.Deps.Compile.run([])
+        end)
+      end)
+
+      message =
+        "Dependency git_repo (#{fixture_path("git_repo")}) no longer requires override_for on deps_repo"
+
+      assert_received {:mix_shell, :info, [^message]}
+    end
+
+    test "errors when more overrides are needed for an app" do
+      deps = [
+        {:deps_repo, "0.1.0", path: "custom/deps_repo"},
+        {:git_repo, "0.2.0", git: MixTest.Case.fixture_path("git_repo"), override_for: []}
+      ]
+
+      with_deps(deps, fn ->
+        in_fixture("deps_status", fn ->
+          Mix.Tasks.Deps.Get.run([])
+          Mix.Tasks.Deps.Compile.run([])
+        end)
+      end)
+
+      message =
+        "Dependency git_repo (#{fixture_path("git_repo")}) requires override_for on deps_repo"
+
+      assert_received {:mix_shell, :info, [^message]}
+    end
+  end
+
   describe "app generation" do
     test "considers runtime from current app on nested deps" do
       Process.put(:custom_deps_git_repo_opts, runtime: false)