Guard specs needing #fork with guard -> { Process.respond_to?(:fork) } do

* Previously they would use `platform_is_not :windows do` but fork() is in
  fact platform-dependent and not available on more than just Windows.
  Notably, JRuby and TruffleRuby cannot implement #fork because the JVM
  does not support it (e.g. the GC expects threads to not die suddenly).
  This seems extremely unlikely to change so IOW the JVM is a platform
  which does not support fork().

Author: eregon

core/io/foreach_spec.rb

@@ -28,7 +28,7 @@
         ScratchPad.recorded.should == ["hello\n", "line2\n"]
       end
 
-      platform_is_not :windows do
+      guard -> { Process.respond_to?(:fork) } do
         it "gets data from a fork when passed -" do
           parent_pid = $$
 

core/io/read_spec.rb

@@ -163,7 +163,7 @@
       end
     end
 
-    platform_is_not :windows do
+    guard -> { Process.respond_to?(:fork) } do
       it "opens a pipe to a fork if the rest is -" do
         str = nil
         suppress_warning do # https://bugs.ruby-lang.org/issues/19630

core/io/readlines_spec.rb

@@ -189,7 +189,7 @@
         lines.should == ["hello\n", "line2\n"]
       end
 
-      platform_is_not :windows do
+      guard -> { Process.respond_to?(:fork) } do
         it "gets data from a fork when passed -" do
           lines = nil
           suppress_warning do # https://bugs.ruby-lang.org/issues/19630

core/process/daemon_spec.rb

@@ -1,10 +1,11 @@
 require_relative '../../spec_helper'
 require_relative 'fixtures/common'
 
-platform_is_not :windows do
-  # macOS 15 is not working this examples
-  return if /darwin/ =~ RUBY_PLATFORM && /15/ =~ `sw_vers -productVersion`
-
+guard -> {
+  Process.respond_to?(:fork) and
+    # macOS 15 is not working for these examples
+    !(/darwin/ =~ RUBY_PLATFORM && /15/ =~ `sw_vers -productVersion`)
+} do
   describe :process_daemon_keep_stdio_open_false, shared: true do
     it "redirects stdout to /dev/null" do
       @daemon.invoke("keep_stdio_open_false_stdout", @object).should == ""
@@ -107,8 +108,12 @@
   end
 end
 
-platform_is :windows do
+guard_not -> { Process.respond_to?(:fork) } do
   describe "Process.daemon" do
+    it "returns false from #respond_to?" do
+      Process.respond_to?(:daemon).should == false
+    end
+
     it "raises a NotImplementedError" do
       -> {
         Process.daemon

core/process/setpgid_spec.rb

@@ -1,7 +1,7 @@
 require_relative '../../spec_helper'
 
 describe "Process.setpgid" do
-  platform_is_not :windows do
+  guard -> { Process.respond_to?(:fork) } do
     # Must use fork as setpgid(2) gives EACCESS after execve()
     it "sets the process group id of the specified process" do
       rd, wr = IO.pipe

core/process/setpgrp_spec.rb

@@ -2,7 +2,7 @@
 
 # TODO: put these in the right files.
 describe "Process.setpgrp and Process.getpgrp" do
-  platform_is_not :windows do
+  guard -> { Process.respond_to?(:fork) } do
     it "sets and gets the process group ID of the calling process" do
       # there are two synchronization points here:
       # One for the child to let the parent know that it has finished

core/process/status/wait_spec.rb

@@ -70,25 +70,27 @@
     end
 
     # This spec is probably system-dependent.
-    it "doesn't block if no child is available when WNOHANG is used" do
-      read, write = IO.pipe
-      pid = Process.fork do
-        read.close
-        Signal.trap("TERM") { Process.exit! }
-        write << 1
+    guard -> { Process.respond_to?(:fork) } do
+      it "doesn't block if no child is available when WNOHANG is used" do
+        read, write = IO.pipe
+        pid = Process.fork do
+          read.close
+          Signal.trap("TERM") { Process.exit! }
+          write << 1
+          write.close
+          sleep
+        end
+
+        Process::Status.wait(pid, Process::WNOHANG).should == nil
+
+        # wait for the child to setup its TERM handler
         write.close
-        sleep
-      end
-
-      Process::Status.wait(pid, Process::WNOHANG).should == nil
-
-      # wait for the child to setup its TERM handler
-      write.close
-      read.read(1)
-      read.close
+        read.read(1)
+        read.close
 
-      Process.kill("TERM", pid)
-      Process::Status.wait.pid.should == pid
+        Process.kill("TERM", pid)
+        Process::Status.wait.pid.should == pid
+      end
     end
 
     it "always accepts flags=0" do

shared/process/fork.rb

@@ -1,5 +1,5 @@
 describe :process_fork, shared: true do
-  platform_is :windows do
+  guard_not -> { Process.respond_to?(:fork) } do
     it "returns false from #respond_to?" do
       # Workaround for Kernel::Method being public and losing the "non-respond_to? magic"
       mod = @object.class.name == "KernelSpecs::Method" ? Object.new : @object
@@ -12,7 +12,7 @@
     end
   end
 
-  platform_is_not :windows do
+  guard -> { Process.respond_to?(:fork) } do
     before :each do
       @file = tmp('i_exist')
       rm_r @file