Move make_enp before fork (#16351)

Pulls creating the `envp` out of the pre-exec stage. It can be prepared entirely before `fork`.

Author: straight-shoota

spec/std/process_spec.cr

@@ -393,10 +393,10 @@ describe Process do
       end
 
       it "errors on invalid key" do
-        expect_raises({% if flag?(:win32) %}ArgumentError{% else %}RuntimeError{% end %}, %(Invalid env key "")) do
+        expect_raises(ArgumentError, %(Invalid env key "")) do
           Process.run(*print_env_command, env: {"" => "baz"})
         end
-        expect_raises({% if flag?(:win32) %}ArgumentError{% else %}RuntimeError{% end %}, %(Invalid env key "foo=bar")) do
+        expect_raises(ArgumentError, %(Invalid env key "foo=bar")) do
           Process.run(*print_env_command, env: {"foo=bar" => "baz"})
         end
       end

src/crystal/system/unix/process.cr

@@ -262,14 +262,16 @@ struct Crystal::System::Process
   def self.spawn(prepared_args, env, clear_env, input, output, error, chdir)
     r, w = FileDescriptor.system_pipe
 
+    envp = Env.make_envp(env, clear_env)
+
     pid = fork(will_exec: true) do
       Crystal::System::Signal.after_fork_before_exec
     end
 
     if !pid
       LibC.close(r)
       begin
-        self.try_replace(prepared_args, env, clear_env, input, output, error, chdir)
+        self.try_replace(prepared_args, envp, input, output, error, chdir)
         byte = 1_u8
         errno = Errno.value.to_i32
         FileDescriptor.write_fully(w, pointerof(byte))
@@ -337,12 +339,11 @@ struct Crystal::System::Process
     {pathname, argv.to_unsafe}
   end
 
-  private def self.try_replace(prepared_args, env, clear_env, input, output, error, chdir)
+  private def self.try_replace(prepared_args, envp, input, output, error, chdir)
     reopen_io(input, ORIGINAL_STDIN)
     reopen_io(output, ORIGINAL_STDOUT)
     reopen_io(error, ORIGINAL_STDERR)
 
-    envp = Env.make_envp(env, clear_env)
     ::Dir.cd(chdir) if chdir
 
     execvpe(*prepared_args, envp)
@@ -456,7 +457,9 @@ struct Crystal::System::Process
   end
 
   def self.replace(command, prepared_args, env, clear_env, input, output, error, chdir)
-    try_replace(prepared_args, env, clear_env, input, output, error, chdir)
+    envp = Env.make_envp(env, clear_env)
+
+    try_replace(prepared_args, envp, input, output, error, chdir)
     raise_exception_from_errno(command)
   end