Add --no-optional-deps to skip optional dependencies for compilation testing

Closes #11798.

5 files changed, 51 insertions, 1 deletions

diff --git a/lib/mix/lib/mix/tasks/compile.elixir.ex b/lib/mix/lib/mix/tasks/compile.elixir.ex
index 903017f00..3922dbc32 100644
--- a/lib/mix/lib/mix/tasks/compile.elixir.ex
+++ b/lib/mix/lib/mix/tasks/compile.elixir.ex
@@ -103,7 +103,7 @@ defmodule Mix.Tasks.Compile.Elixir do
 
     manifest = manifest()
     base = xref_exclude_opts(project[:elixirc_options] || [], project)
-    cache_key = {base, srcs}
+    cache_key = {base, srcs, "--no-optional-deps" in args}
 
     opts =
       base
diff --git a/lib/mix/lib/mix/tasks/compile.ex b/lib/mix/lib/mix/tasks/compile.ex
index 46c41f8e3..2cbb05241 100644
--- a/lib/mix/lib/mix/tasks/compile.ex
+++ b/lib/mix/lib/mix/tasks/compile.ex
@@ -54,6 +54,9 @@ defmodule Mix.Tasks.Compile do
     * `--no-compile` - does not actually compile, only loads code and perform checks
     * `--no-deps-check` - skips checking of dependencies
     * `--no-elixir-version-check` - does not check Elixir version
+    * `--no-optional-deps` - does not compile or load optional deps. Useful for testing
+      if a library still successfully compiles without optional dependencies (which is the
+      default case with dependencies)
     * `--no-protocol-consolidation` - skips protocol consolidation
     * `--no-validate-compile-env` - does not validate the application compile environment
     * `--return-errors` - returns error status and diagnostics instead of exiting on error
diff --git a/lib/mix/lib/mix/tasks/deps.loadpaths.ex b/lib/mix/lib/mix/tasks/deps.loadpaths.ex
index 9db870d3e..eb30eb9ae 100644
--- a/lib/mix/lib/mix/tasks/deps.loadpaths.ex
+++ b/lib/mix/lib/mix/tasks/deps.loadpaths.ex
@@ -18,12 +18,21 @@ defmodule Mix.Tasks.Deps.Loadpaths do
     * `--no-deps-check` - does not check or compile deps, only load available ones
     * `--no-elixir-version-check` - does not check Elixir version
     * `--no-load-deps` - does not add deps loadpaths to the code path
+    * `--no-optional-deps` - does not compile or load optional deps
 
   """
 
   @impl true
   def run(args) do
     all = Mix.Dep.load_and_cache()
+
+    all =
+      if "--no-optional-deps" in args do
+        for dep <- all, dep.opts[:optional] != true, do: dep
+      else
+        all
+      end
+
     config = Mix.Project.config()
 
     unless "--no-elixir-version-check" in args do
diff --git a/lib/mix/lib/mix/tasks/loadpaths.ex b/lib/mix/lib/mix/tasks/loadpaths.ex
index 303f8b987..dd64d3b2a 100644
--- a/lib/mix/lib/mix/tasks/loadpaths.ex
+++ b/lib/mix/lib/mix/tasks/loadpaths.ex
@@ -22,6 +22,7 @@ defmodule Mix.Tasks.Loadpaths do
     * `--no-deps-check` - does not check dependencies, only load available ones
     * `--no-elixir-version-check` - does not check Elixir version
     * `--no-load-deps` - does not add deps loadpaths to the code path
+    * `--no-optional-deps` - does not compile or load optional deps
 
   """
   @impl true
diff --git a/lib/mix/test/mix/tasks/compile.elixir_test.exs b/lib/mix/test/mix/tasks/compile.elixir_test.exs
index 9bc5b948d..a2258f11c 100644
--- a/lib/mix/test/mix/tasks/compile.elixir_test.exs
+++ b/lib/mix/test/mix/tasks/compile.elixir_test.exs
@@ -1494,4 +1494,41 @@ defmodule Mix.Tasks.Compile.ElixirTest do
       refute_received {:mix_shell, :info, ["Compiled lib/c.ex"]}
     end)
   end
+
+  defmodule GitApp do
+    def project do
+      [
+        app: :git_app,
+        version: "0.1.0",
+        deps: [
+          {:git_repo, "0.1.0", git: fixture_path("git_repo"), optional: true}
+        ]
+      ]
+    end
+  end
+
+  test "compiles without optional dependencies" do
+    in_fixture("no_mixfile", fn ->
+      Mix.Project.push(GitApp)
+
+      File.write!("lib/a.ex", """
+      defmodule A do
+        def hello, do: GitRepo.hello()
+      end
+      """)
+
+      assert capture_io(:stderr, fn ->
+               Mix.Tasks.Compile.run(["--no-optional-deps"]) == :ok
+             end) =~ "GitRepo.hello/0 is undefined"
+    end)
+  end
+
+  test "recompiles if --no-optional-deps change" do
+    in_fixture("no_mixfile", fn ->
+      Mix.Project.push(MixTest.Case.Sample)
+      assert Mix.Tasks.Compile.Elixir.run([]) == {:ok, []}
+      assert Mix.Tasks.Compile.Elixir.run([]) == {:noop, []}
+      assert Mix.Tasks.Compile.Elixir.run(["--no-optional-deps"]) == {:ok, []}
+    end)
+  end
 end