Fix env outdated deps compilation

We should only avoid cleaning for path dependencies.
Fetch dependencies should go through the previous process.

Closes #15467.

Author: josevalim

lib/mix/lib/mix/dep.ex

@@ -486,20 +486,12 @@ defmodule Mix.Dep do
   @doc """
   Returns `true` if the dependency is compilable.
   """
+  def compilable?(%Mix.Dep{status: {:vsnlock, _}}), do: true
+  def compilable?(%Mix.Dep{status: {:noappfile, {_, _}}}), do: true
+  def compilable?(%Mix.Dep{status: {:scmlock, _}}), do: true
+  def compilable?(%Mix.Dep{status: :compile}), do: true
   def compilable?(%Mix.Dep{status: :envoutdated}), do: true
-  def compilable?(dep), do: force_compilable?(dep)
-
-  @doc """
-  Returns `true` if the dependency is force compilable.
-
-  This is a subset of compilable. This is used in `deps.compile` to
-  clean the build path before compiling.
-  """
-  def force_compilable?(%Mix.Dep{status: {:vsnlock, _}}), do: true
-  def force_compilable?(%Mix.Dep{status: {:noappfile, {_, _}}}), do: true
-  def force_compilable?(%Mix.Dep{status: {:scmlock, _}}), do: true
-  def force_compilable?(%Mix.Dep{status: :compile}), do: true
-  def force_compilable?(_), do: false
+  def compilable?(_), do: false
 
   @doc """
   Formats a dependency for printing.

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

@@ -125,7 +125,7 @@ defmodule Mix.Tasks.Deps.Compile do
 
     # If a dependency was marked as fetched or with an out of date lock
     # or missing the app file, we always compile it from scratch.
-    if force? or Mix.Dep.force_compilable?(dep) do
+    if force? or clean_before_compile?(dep) do
       File.rm_rf!(Path.join([Mix.Project.build_path(), "lib", Atom.to_string(dep.app)]))
     end
 
@@ -402,6 +402,20 @@ defmodule Mix.Tasks.Deps.Compile do
     end
   end
 
+  # Most compilable statuses mean the dependency source, lock, app file, or build
+  # metadata changed in a way that requires removing the old build before
+  # compiling. :envoutdated is different: path dependencies can be incrementally
+  # recompiled from their existing build, but fetched dependencies must be cleaned
+  # first so stale BEAM files do not validate against the new compile environment
+  # before the dependency has a chance to rebuild.
+  defp clean_before_compile?(%Mix.Dep{status: :envoutdated, scm: scm}) do
+    scm.fetchable?()
+  end
+
+  defp clean_before_compile?(dep) do
+    Mix.Dep.compilable?(dep)
+  end
+
   defp deps_compile_feedback(app) do
     if Mix.install?() do
       "Errors may have been logged above. You may run Mix.install/2 to try again or " <>

lib/mix/test/mix/tasks/deps_test.exs

@@ -73,6 +73,18 @@ defmodule Mix.Tasks.DepsTest do
     end
   end
 
+  defmodule FetchableGitRepoDepApp do
+    def project do
+      [
+        app: :git_sample,
+        version: "0.1.0",
+        deps: [
+          {:git_repo, "0.1.0", git: MixTest.Case.fixture_path("git_repo")}
+        ]
+      ]
+    end
+  end
+
   ## deps
 
   test "prints list of dependencies and their status alphabetically" do
@@ -910,7 +922,51 @@ defmodule Mix.Tasks.DepsTest do
       assert Application.spec(:raw_repo, :vsn)
     end)
   after
-    Application.delete_env(:raw_repo, :compile_env, persistent: true)
+    Application.delete_env(:anyapp, :anything, persistent: true)
+  end
+
+  test "recompiles fetchable dependencies when compile env changed" do
+    in_fixture("deps_status", fn ->
+      File.mkdir_p!("config")
+      File.write!("config/config.exs", "import Config\n")
+
+      Mix.Project.push(FetchableGitRepoDepApp)
+      Mix.Tasks.Deps.Get.run([])
+
+      File.write!("deps/git_repo/lib/git_repo.ex", """
+      Application.compile_env(:anyapp, :anything)
+
+      defmodule GitRepo do
+        def hello do
+          "World"
+        end
+      end
+      """)
+
+      Mix.Tasks.Loadconfig.load_compile("config/config.exs")
+      Mix.Task.run("compile", [])
+      assert Application.spec(:git_repo, :vsn)
+
+      File.write!("config/config.exs", """
+      import Config
+      config :anyapp, :anything, :anyvalue
+      """)
+
+      Application.unload(:git_repo)
+      Mix.ProjectStack.pop()
+      Mix.Task.clear()
+      Mix.Project.push(FetchableGitRepoDepApp)
+      purge([GitRepo])
+      Mix.Tasks.Loadconfig.load_compile("config/config.exs")
+
+      Mix.Task.run("compile", [])
+
+      assert_receive {:mix_shell, :info, ["Generated git_repo app"]}
+      assert Application.spec(:git_repo, :vsn)
+    end)
+  after
+    Application.delete_env(:anyapp, :anything, persistent: true)
+    purge([GitRepo, GitRepo.MixProject])
   end
 
   test "does not compile deps that have explicit option" do