gem.rb: detect external HAL by hal-<short>-* naming

67f137e201 introduced spec.hal_pattern on the target gem to
declare its expected HAL provider names.  But the decision to
override is naturally an opt-in choice belonging to the external
HAL gem (or build_config), not the target.  Drop hal_pattern and
hardcode the naming rule in resolve_external_hal!: a gem named
`hal-<short>-<conf>` overrides the gem whose last `-`-separated
segment is <short>.  No spec attribute on the target gem; no flag
on add_dependency; the convention does all the work.

The pre-be6413f0d8 convention was `hal-<platform>-<gem>` (e.g.,
hal-posix-task) for platform sort across gems.  Now that the
common platforms live under ports/, sorting by which target gem
a HAL is for is more useful, so the order is reversed:
`hal-<gem>-<conf>` (e.g., hal-task-glib).

ref #6825

Co-authored-by: Claude <noreply@anthropic.com>

lib/mruby/gem.rb

@@ -26,7 +26,6 @@ module MRuby
 
       attr_accessor :rbfiles, :objs
       attr_reader :port_objs
-      attr_accessor :hal_pattern
       attr_writer :test_objs, :test_rbfiles
       attr_accessor :test_args, :test_preload
 
@@ -67,7 +66,7 @@ module MRuby
         # chain: later names act as defaults for gems that don't ship
         # a port for the earlier names.  These objs are tracked
         # separately so List#resolve_external_hal! can drop them when
-        # an external HAL provider matching spec.hal_pattern is loaded.
+        # an external HAL provider (gem named hal-<short>-*) is loaded.
         @port_objs = []
         build.effective_ports.each do |port|
           port_dir = "#{@dir}/ports/#{port}"
@@ -466,22 +465,23 @@ module MRuby
         resolve_external_hal!
       end
 
-      # If a gem declares `spec.hal_pattern = /regex/`, any other gem
-      # whose name matches the regex is treated as the external HAL
-      # provider for that gem -- the target gem's ports/* sources are
-      # dropped from its object list (the matching gem itself supplies
-      # the implementation).  Two or more matches is a build error.
+      # A gem named `hal-<short>-<conf>` is treated as the external
+      # HAL provider for the gem whose name's last `-`-separated
+      # segment is <short> (e.g., hal-task-glib provides the HAL for
+      # mruby-task).  The target gem's ports/* sources are dropped
+      # from its object list -- the matching gem supplies the
+      # implementation.  Two or more matches is a build error.
       def resolve_external_hal!
         each do |target|
-          next unless target.hal_pattern
-          overriders = select { |g| g != target && g.name =~ target.hal_pattern }
+          next if target.port_objs.nil? || target.port_objs.empty?
+          short = target.name.split('-').last
+          pattern = /\Ahal-#{Regexp.escape(short)}-.+\z/
+          overriders = select { |g| g != target && g.name =~ pattern }
           next if overriders.empty?
           if overriders.size > 1
-            fail "Multiple gems match #{target.hal_pattern.inspect} as " \
-                 "HAL provider for '#{target.name}': " +
+            fail "Multiple HAL providers for '#{target.name}': " +
                  overriders.map(&:name).join(", ")
           end
-          next if target.port_objs.nil? || target.port_objs.empty?
           target.objs.reject! { |o| target.port_objs.include?(o) }
         end
       end

mrbgems/mruby-task/mrbgem.rake

@@ -6,10 +6,6 @@ MRuby::Gem::Specification.new('mruby-task') do |spec|
   # Enable task scheduler globally (required for vm.c integration)
   spec.build.defines << 'MRB_USE_TASK_SCHEDULER'
 
-  # A gem named hal-<name>-task (declaring add_dependency 'mruby-task')
-  # replaces the built-in ports/<conf.ports>/ HAL implementation.
-  spec.hal_pattern = /\Ahal-.*-task\z/
-
   if spec.for_windows?
     spec.linker.libraries << "winmm"
   end