Make compiler module purging opt-in

We run it before module verification but,
as module verification now loads many modules,
that was negatively impacting compilation times.

Author: josevalim

lib/elixir/lib/kernel/parallel_compiler.ex

@@ -35,7 +35,8 @@ defmodule Kernel.ParallelCompiler do
           dest: Path.t(),
           beam_timestamp: term(),
           return_diagnostics: boolean(),
-          max_concurrency: pos_integer()
+          max_concurrency: pos_integer(),
+          purge_compiler_modules: boolean()
         ]
 
   @typedoc """
@@ -200,6 +201,9 @@ defmodule Kernel.ParallelCompiler do
     * `:profile` - if set to `:time` measure the compilation time of each compilation cycle
        and group pass checker
 
+    * `:purge_compiler_modules` - if set to `true`, automatically purge compilation modules
+      after compilation (see `Code.purge_compiler_modules/0`)
+
     * `:dest` - the destination directory for the BEAM files. When using `compile/2`,
       this information is only used to properly annotate the BEAM files before
       they are loaded into memory. If you want a file to actually be written to
@@ -338,6 +342,13 @@ defmodule Kernel.ParallelCompiler do
     threshold = Keyword.get(options, :long_compilation_threshold, 10) * 1000
     timer_ref = Process.send_after(self(), :threshold_check, threshold)
 
+    purge_compiler_modules =
+      if Keyword.get(options, :purge_compiler_modules, false) do
+        fn -> :elixir_code_server.cast(:purge_compiler_modules) end
+      else
+        fn -> :ok end
+      end
+
     {outcome, state} =
       spawn_workers(files, %{}, %{}, [], %{}, [], [], %{
         beam_timestamp: Keyword.get(options, :beam_timestamp),
@@ -353,7 +364,8 @@ defmodule Kernel.ParallelCompiler do
         long_compilation_threshold: threshold,
         schedulers: schedulers,
         checker: checker,
-        verification?: Keyword.get(options, :verification, true)
+        verification?: Keyword.get(options, :verification, true),
+        purge_compiler_modules: purge_compiler_modules
       })
 
     Process.cancel_timer(state.timer_ref)
@@ -570,11 +582,11 @@ defmodule Kernel.ParallelCompiler do
 
     case cycle_return do
       {:runtime, dependent_modules, extra_warnings} ->
-        :elixir_code_server.cast(:purge_compiler_modules)
+        state.purge_compiler_modules.()
         verify_modules(result, extra_warnings ++ warnings, dependent_modules, state)
 
       {:compile, [], extra_warnings} ->
-        :elixir_code_server.cast(:purge_compiler_modules)
+        state.purge_compiler_modules.()
         verify_modules(result, extra_warnings ++ warnings, [], state)
 
       {:compile, more, extra_warnings} ->
@@ -879,8 +891,7 @@ defmodule Kernel.ParallelCompiler do
   end
 
   defp return_error(warnings, errors, state, fun) do
-    # Also prune compiler modules in case of errors
-    :elixir_code_server.cast(:purge_compiler_modules)
+    state.purge_compiler_modules.()
 
     errors =
       Enum.map(errors, fn {%{file: file} = diagnostic, read_snippet} ->

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

@@ -1039,9 +1039,9 @@ defmodule Mix.Compilers.Elixir do
     parent = self()
     compilation_threshold = opts[:long_compilation_threshold] || 10
     verification_threshold = opts[:long_verification_threshold] || 10
-    profile = opts[:profile]
     verbose = Keyword.get(opts, :verbose, false)
     verification = Keyword.get(opts, :verification, true)
+    extra_opts = Keyword.take(opts, [:profile, :purge_compiler_modules])
 
     if not verification and not Mix.debug?() do
       Mix.shell().error("--no-verification flag is only recommended with MIX_DEBUG=1")
@@ -1078,11 +1078,12 @@ defmodule Mix.Compilers.Elixir do
           long_verification_threshold: verification_threshold,
           beam_timestamp: timestamp,
           return_diagnostics: true,
-          profile: profile,
           verification: verification
         ]
 
-        response = Kernel.ParallelCompiler.compile_to_path(stale, dest, compile_opts)
+        response =
+          Kernel.ParallelCompiler.compile_to_path(stale, dest, compile_opts ++ extra_opts)
+
         send(parent, {ref, response})
       end)
 

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

@@ -78,6 +78,8 @@ defmodule Mix.Tasks.Compile.Elixir do
       the current working directory to be checked
     * `--purge-consolidation-path-if-stale PATH` - deletes and purges modules in the
       given protocol consolidation path if compilation is required
+    * `--purge-compiler-modules` - automatically purge compilation modules
+      after compilation (see `Code.purge_compiler_modules/0`)
     * `--profile` - if set to `time`, outputs timing information of compilation steps
     * `--tracer` - adds a compiler tracer in addition to any specified in the `mix.exs` file
     * `--verbose` - prints each file being compiled
@@ -110,6 +112,7 @@ defmodule Mix.Tasks.Compile.Elixir do
     long_compilation_threshold: :integer,
     long_verification_threshold: :integer,
     purge_consolidation_path_if_stale: :string,
+    purge_compiler_modules: :boolean,
     profile: :string,
     all_warnings: :boolean,
     verification: :boolean,