Allow fetching for different arch.

Library/Homebrew/cask/cask.rb

@@ -322,6 +322,7 @@ module Cask
 
       hash_keys_to_skip = %w[outdated installed versions]
 
+      begin
         if @dsl.on_system_blocks_exist?
           [:arm, :intel].each do |arch|
             MacOSVersions::SYMBOLS.each_key do |os_name|
@@ -343,8 +344,10 @@ module Cask
             end
           end
         end
-
+      ensure
         Homebrew::SimulateSystem.clear
+      end
+
       refresh
 
       hash["variations"] = variations

Library/Homebrew/cmd/fetch.rb

@@ -20,6 +20,10 @@ module Homebrew
         Download a bottle (if available) or source packages for <formula>e
         and binaries for <cask>s. For files, also print SHA-256 checksums.
       EOS
+      # This is needed for testing cask downloads on CI.
+      flag "--arch=",
+           description: "Download for the given arch.",
+           hidden:      true
       flag "--bottle-tag=",
            description: "Download a bottle for given tag."
       switch "--HEAD",
@@ -66,6 +70,10 @@ module Homebrew
   def self.fetch
     args = fetch_args.parse
 
+    if (arch = args.arch)
+      SimulateSystem.arch = arch.to_sym
+    end
+
     bucket = if args.deps?
       args.named.to_formulae_and_casks.flat_map do |formula_or_cask|
         case formula_or_cask

Library/Homebrew/dev-cmd/bump-cask-pr.rb

@@ -144,7 +144,7 @@ module Homebrew
 
               replacement_pairs << [new_hash_cask.sha256.to_s, download.sha256]
             end
-
+          ensure
             Homebrew::SimulateSystem.clear
           end
         elsif new_hash.present?

Library/Homebrew/formula.rb

@@ -2219,6 +2219,7 @@ class Formula
 
     os_versions = [*MacOSVersions::SYMBOLS.keys, :linux]
 
+    begin
       if path.exist? && self.class.on_system_blocks_exist?
         formula_contents = path.read
         [:arm, :intel].each do |arch|
@@ -2244,8 +2245,9 @@ class Formula
           end
         end
       end
-
+    ensure
       Homebrew::SimulateSystem.clear
+    end
 
     hash["variations"] = variations
     hash

Library/Homebrew/readall.rb

@@ -103,16 +103,18 @@ module Readall
             bottle_tag = Utils::Bottles::Tag.new(system: os_name, arch: arch)
             next unless bottle_tag.valid_combination?
 
+            begin
               Homebrew::SimulateSystem.arch = arch
               Homebrew::SimulateSystem.os = os_name
 
               success = false unless valid_formulae?(tap.formula_files, bottle_tag: bottle_tag)
               success = false unless valid_casks?(tap.cask_files, bottle_tag: bottle_tag)
-
+            ensure
               Homebrew::SimulateSystem.clear
             end
           end
         end
+      end
       success
     end