Ensure system_env is applied for Elixir deps, closes #15095

Author: josevalim

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

@@ -209,31 +209,38 @@ defmodule Mix.Tasks.Deps.Compile do
   end
 
   defp do_mix(dep, _config) do
-    Mix.Dep.in_dependency(dep, fn _ ->
-      config = Mix.Project.config()
-
-      if req = old_elixir_req(config) do
-        Mix.shell().error(
-          "warning: the dependency #{inspect(dep.app)} requires Elixir #{inspect(req)} " <>
-            "but you are running on v#{System.version()}"
-        )
-      end
-
-      try do
-        options = ["--from-mix-deps-compile", "--no-warnings-as-errors", "--no-code-path-pruning"]
-        res = Mix.Task.run("compile", options)
-        match?({:ok, _}, res)
-      catch
-        kind, reason ->
-          app = dep.app
+    Mix.Dep.Loader.with_system_env(dep, fn ->
+      Mix.Dep.in_dependency(dep, fn _ ->
+        config = Mix.Project.config()
 
+        if req = old_elixir_req(config) do
           Mix.shell().error(
-            "could not compile dependency #{inspect(app)}, \"mix compile\" failed. " <>
-              deps_compile_feedback(app)
+            "warning: the dependency #{inspect(dep.app)} requires Elixir #{inspect(req)} " <>
+              "but you are running on v#{System.version()}"
           )
-
-          :erlang.raise(kind, reason, __STACKTRACE__)
-      end
+        end
+
+        try do
+          options = [
+            "--from-mix-deps-compile",
+            "--no-warnings-as-errors",
+            "--no-code-path-pruning"
+          ]
+
+          res = Mix.Task.run("compile", options)
+          match?({:ok, _}, res)
+        catch
+          kind, reason ->
+            app = dep.app
+
+            Mix.shell().error(
+              "could not compile dependency #{inspect(app)}, \"mix compile\" failed. " <>
+                deps_compile_feedback(app)
+            )
+
+            :erlang.raise(kind, reason, __STACKTRACE__)
+        end
+      end)
     end)
   end
 

lib/mix/test/mix/dep_test.exs

@@ -355,7 +355,29 @@ defmodule Mix.DepTest do
     end)
   end
 
-  test "deps with system_env set" do
+  @compile {:no_warn_undefined, [{A, :env, 0}]}
+  test "mix dep with system_env set" do
+    system_env = [{"CONTENTS_FROM_ENV", "contents dep test"}]
+    deps = [{:ok, "~> 0.1", path: "deps/ok", system_env: system_env}]
+
+    with_deps(deps, fn ->
+      in_fixture("deps_status", fn ->
+        File.mkdir_p!("deps/ok/lib")
+
+        File.write!("deps/ok/lib/a.ex", """
+        defmodule A do
+          def env, do: unquote(System.fetch_env!("CONTENTS_FROM_ENV"))
+        end
+        """)
+
+        Mix.Tasks.Deps.Get.run([])
+        Mix.Tasks.Deps.Compile.run([])
+        assert A.env() == "contents dep test"
+      end)
+    end)
+  end
+
+  test "rebar dep with system_env set" do
     file_path = tmp_path("load dependency with env vars/dep-test")
     dep_path = tmp_path("rebar_dep")