Allow verification to be disabled with MIX_DEBUG=1

Author: josevalim

lib/elixir/lib/kernel/parallel_compiler.ex

@@ -162,6 +162,10 @@ defmodule Kernel.ParallelCompiler do
       threshold, the `:each_long_verification` callback is invoked. Defaults to
       `10` seconds.
 
+    * `:verification` (since v1.19.0) - if code verification, such as unused functions,
+      deprecation warnings, and type checking should run. Defaults to `true`.
+      We recommend disabling it only for debugging purposes.
+
     * `:profile` - if set to `:time` measure the compilation time of each compilation cycle
        and group pass checker
 
@@ -310,7 +314,8 @@ defmodule Kernel.ParallelCompiler do
         timer_ref: timer_ref,
         long_compilation_threshold: threshold,
         schedulers: schedulers,
-        checker: checker
+        checker: checker,
+        verification?: Keyword.get(options, :verification, true)
       })
 
     Process.cancel_timer(state.timer_ref)
@@ -358,22 +363,25 @@ defmodule Kernel.ParallelCompiler do
   defp verify_modules(result, compile_warnings, dependent_modules, state) do
     modules = write_module_binaries(result, state.output, state.beam_timestamp)
     _ = state.after_compile.()
-    runtime_warnings = maybe_check_modules(modules, dependent_modules, state)
+
+    runtime_warnings =
+      if state.verification? do
+        profile(
+          state,
+          fn ->
+            num_modules = length(modules) + length(dependent_modules)
+            "group pass check of #{num_modules} modules"
+          end,
+          fn -> Module.ParallelChecker.verify(state.checker, dependent_modules) end
+        )
+      else
+        []
+      end
+
     info = %{compile_warnings: Enum.reverse(compile_warnings), runtime_warnings: runtime_warnings}
     {{:ok, modules, info}, state}
   end
 
-  defp maybe_check_modules(compiled_modules, runtime_modules, state) do
-    profile(
-      state,
-      fn ->
-        num_modules = length(compiled_modules) + length(runtime_modules)
-        "group pass check of #{num_modules} modules"
-      end,
-      fn -> Module.ParallelChecker.verify(state.checker, runtime_modules) end
-    )
-  end
-
   defp profile_init(:time), do: {:time, System.monotonic_time(), 0}
   defp profile_init(nil), do: :none
 

lib/mix/lib/mix/compilers/elixir.ex

@@ -1004,7 +1004,12 @@ defmodule Mix.Compilers.Elixir do
     compilation_threshold = opts[:long_compilation_threshold] || 10
     verification_threshold = opts[:long_verification_threshold] || 10
     profile = opts[:profile]
-    verbose = opts[:verbose] || false
+    verbose = Keyword.get(opts, :verbose, false)
+    verification = Keyword.get(opts, :verification, true)
+
+    if not verification and not Mix.debug?() do
+      Mix.shell().error("--no-verification flag is only recommended with MIX_DEBUG=1")
+    end
 
     pid =
       spawn_link(fn ->
@@ -1035,9 +1040,10 @@ defmodule Mix.Compilers.Elixir do
           end,
           long_compilation_threshold: compilation_threshold,
           long_verification_threshold: verification_threshold,
-          profile: profile,
           beam_timestamp: timestamp,
-          return_diagnostics: true
+          return_diagnostics: true,
+          profile: profile,
+          verification: verification
         ]
 
         response = Kernel.ParallelCompiler.compile_to_path(stale, dest, compile_opts)

lib/mix/lib/mix/tasks/compile.elixir.ex

@@ -70,6 +70,8 @@ defmodule Mix.Tasks.Compile.Elixir do
       (in seconds) to `N` (see the docs for `Kernel.ParallelCompiler.compile/2`)
     * `--long-verification-threshold N` - sets the "long verification" threshold
       (in seconds) to `N` (see the docs for `Kernel.ParallelCompiler.compile/2`)
+    * `--no-verification` - disables code verification, such as unused functions,
+      deprecation warnings, and type checking. It must be used alongside `MIX_DEBUG=1`
     * `--purge-consolidation-path-if-stale PATH` - deletes and purges modules in the
       given protocol consolidation path if compilation is required
     * `--profile` - if set to `time`, outputs timing information of compilation steps
@@ -106,6 +108,7 @@ defmodule Mix.Tasks.Compile.Elixir do
     purge_consolidation_path_if_stale: :string,
     profile: :string,
     all_warnings: :boolean,
+    verification: :boolean,
     tracer: :keep
   ]
 

lib/mix/test/mix/tasks/compile.elixir_test.exs

@@ -1666,6 +1666,16 @@ defmodule Mix.Tasks.Compile.ElixirTest do
       assert output =~ "B.foo/0 is undefined or private"
       assert output =~ "B.bar/0 is undefined or private"
       assert output =~ "AFTER_VERIFY"
+
+      # But we can also disable verification if we want to
+      output =
+        capture_io(:stderr, fn ->
+          Mix.Tasks.Compile.Elixir.run(["--no-verification", "--force"])
+        end)
+
+      refute output =~ "B.foo/0 is undefined or private"
+      refute output =~ "B.bar/0 is undefined or private"
+      refute output =~ "AFTER_VERIFY"
     end)
   end