bottles: support :all tag.

This allows the creation of bottles which will be used by any macOS
version, architecture or OS (i.e. macOS or Linux).

Add `TODO` stubs for where the bottle generation logic should be
implemented.

Library/Homebrew/dev-cmd/bottle.rb

@@ -585,6 +585,12 @@ module Homebrew
   def merge(args:)
     bottles_hash = merge_json_files(parse_json_files(args.named))
 
+    # TODO: deduplicate --no-json bottles by:
+    # 1. throwing away bottles for newer versions of macOS if their SHA256 is
+    #    identical
+    # 2. generating `all: $SHA256` bottles that can be used on macOS and Linux
+    #    i.e. need to be `any_skip_relocation` and contain no ELF/MachO files.
+
     any_cellars = ["any", "any_skip_relocation"]
     bottles_hash.each do |formula_name, bottle_hash|
       ohai formula_name

Library/Homebrew/test/dev-cmd/bottle_spec.rb

@@ -493,7 +493,8 @@ describe "brew bottle" do
       end
     end
 
-    specify "::merge_json_files" do
+    describe "::merge_json_files" do
+      it "merges JSON files" do
         bottles_hash = homebrew.merge_json_files(
           [hello_hash_big_sur, hello_hash_catalina, unzip_hash_big_sur, unzip_hash_catalina],
         )
@@ -526,6 +527,11 @@ describe "brew bottle" do
         )
       end
 
+      # TODO: add deduplication tests e.g.
+      # it "deduplicates JSON files with matching macOS checksums"
+      # it "deduplicates JSON files with matching OS checksums" do
+    end
+
     describe "#merge_bottle_spec" do
       it "allows new bottle hash to be empty" do
         valid_keys = [:root_url, :prefix, :cellar, :rebuild, :sha256]

Library/Homebrew/utils/bottles.rb

@@ -87,6 +87,8 @@ module Utils
 
       sig { params(value: Symbol).returns(T.attached_class) }
       def self.from_symbol(value)
+        return new(system: :all, arch: :all) if value == :all
+
         @all_archs_regex ||= begin
           all_archs = Hardware::CPU::ALL_ARCHS.map(&:to_s)
           /
@@ -118,7 +120,9 @@ module Utils
 
       sig { returns(Symbol) }
       def to_sym
-        if macos? && arch == :x86_64
+        if system == :all && arch == :all
+          :all
+        elsif macos? && arch == :x86_64
           system
         else
           "#{arch}_#{system}".to_sym
@@ -219,7 +223,11 @@ module Utils
       private
 
       def find_matching_tag(tag, no_older_versions: false)
-        tag if key?(tag.to_sym)
+        if key?(tag.to_sym)
+          tag
+        elsif key?(:all)
+          Tag.from_symbol(:all)
+        end
       end
     end
   end