install steps: add {{arch}} template token

Library/Homebrew/cask/artifact/install_steps.rb

@@ -54,6 +54,7 @@ def run_steps(command, phase: :install)
           "context" => {
             "name"          => cask.name,
             "token"         => cask.token,
+            "arch"          => cask.arch,
             "version"       => cask.version.to_s,
             "staged_path"   => cask.staged_path.to_s,
             "caskroom_path" => cask.caskroom_path.to_s,

Library/Homebrew/cask_artifact.rb

@@ -23,6 +23,9 @@ class InstallStepsContext
     sig { returns(String) }
     attr_reader :token
 
+    sig { returns(T.nilable(String)) }
+    attr_reader :arch
+
     sig { returns(String) }
     attr_reader :version
 
@@ -42,6 +45,7 @@ class InstallStepsContext
     def initialize(context)
       @name = T.let(context.fetch("name"), T.any(String, T::Array[String]))
       @token = T.let(context.fetch("token"), String)
+      @arch = T.let(context["arch"], T.nilable(String))
       @version = T.let(context.fetch("version"), String)
       @staged_path = T.let(Pathname(context.fetch("staged_path")), Pathname)
       @caskroom_path = T.let(Pathname(context.fetch("caskroom_path")), Pathname)

Library/Homebrew/install_steps.rb

@@ -104,6 +104,11 @@ def token
         "{{token}}"
       end
 
+      sig { returns(String) }
+      def arch
+        "{{arch}}"
+      end
+
       sig { returns(TemplateVersion) }
       def version
         TEMPLATE_VERSION
@@ -1412,6 +1417,8 @@ def template_token_value(token)
           context_value(:name)&.to_s
         when "name"
           context_name
+        when "arch"
+          context_arch
         when "token"
           context_value(:token)&.to_s
         when "user"
@@ -1496,6 +1503,15 @@ def context_name
         value&.to_s
       end
 
+      sig { returns(T.nilable(String)) }
+      def context_arch
+        # Casks without a matching `arch` stanza value expand to an empty
+        # string, matching the deprecated `postflight` block.
+        return unless @context.respond_to?(:arch)
+
+        context_value(:arch).to_s
+      end
+
       sig { returns(T.nilable(String)) }
       def context_version
         context_value(:version)&.to_s

Library/Homebrew/rubocops/shared/install_steps_helper.rb

@@ -439,7 +439,9 @@ def allowed_step_template_node?(node)
 
         send_node = T.cast(node, RuboCop::AST::SendNode)
         return false if send_node.arguments.present?
-        return [:formula_name, :name, :token, :version].include?(send_node.method_name) if send_node.receiver.nil?
+        if send_node.receiver.nil?
+          return [:arch, :formula_name, :name, :token, :version].include?(send_node.method_name)
+        end
 
         return false unless (receiver = send_node.receiver)&.send_type?
 
@@ -749,9 +751,9 @@ def dstr_permission_path(node)
             source << content.dump.delete_prefix('"').delete_suffix('"')
             true
           elsif child.begin_type? && allowed_step_template_node?(child)
-            interpolation = "\#{#{child.source}}"
-            path << interpolation
-            source << interpolation
+            # `child.source` already carries the `#{}` delimiters.
+            path << child.source
+            source << child.source
             true
           else
             false

Library/Homebrew/test/install_steps_spec.rb

@@ -323,6 +323,38 @@ def create_executable(path)
     expect(written).to include("literal = {{unknown}} {single}")
   end
 
+  specify "expands the cask arch token" do
+    context.define_singleton_method(:arch) { "-m1" }
+    steps = Homebrew::InstallSteps::DSL.build(default_base: :var) do
+      write_file "arch", "example#{arch}.app", append_newline: true
+    end
+
+    Homebrew::InstallSteps::Runner.new(context:).run(steps)
+
+    expect((root/"var/arch").read).to eq("example-m1.app\n")
+  end
+
+  specify "expands the cask arch token to an empty string without a matching value" do
+    context.define_singleton_method(:arch) { nil }
+    steps = Homebrew::InstallSteps::DSL.build(default_base: :var) do
+      write_file "arch", "example{{arch}}.app", append_newline: true
+    end
+
+    Homebrew::InstallSteps::Runner.new(context:).run(steps)
+
+    expect((root/"var/arch").read).to eq("example.app\n")
+  end
+
+  specify "leaves the arch token verbatim for a context without an arch" do
+    steps = Homebrew::InstallSteps::DSL.build(default_base: :var) do
+      write_file "arch", "example{{arch}}.app", append_newline: true
+    end
+
+    Homebrew::InstallSteps::Runner.new(context:).run(steps)
+
+    expect((root/"var/arch").read).to eq("example{{arch}}.app\n")
+  end
+
   specify "expands formula and cask identity tokens" do
     context.define_singleton_method(:name) { "example-formula" }
     context.define_singleton_method(:token) { "example-cask" }

Library/Homebrew/test/rubocops/cask/install_steps_spec.rb

@@ -492,6 +492,31 @@
     CASK
   end
 
+  it "autocorrects permission work using the arch template helper" do
+    expect_offense <<~'CASK'
+      cask "foo" do
+        version :latest
+        sha256 :no_check
+
+        postflight do
+        ^^^^^^^^^^^^^ Use `postflight_steps` for simple file preparation.
+          set_ownership "#{staged_path}/foo-#{arch}"
+        end
+      end
+    CASK
+
+    expect_correction <<~'CASK'
+      cask "foo" do
+        version :latest
+        sha256 :no_check
+
+        postflight_steps do
+          set_ownership "foo-#{arch}"
+        end
+      end
+    CASK
+  end
+
   it "does not autocorrect dynamic, unsupported or mixed permission work" do
     expect_offense <<~'CASK'
       cask "foo" do
@@ -500,7 +525,7 @@
 
         postflight do
         ^^^^^^^^^^^^^ Casks must use `postflight_steps` instead of `postflight`.
-          set_ownership "#{staged_path}/foo-#{arch}"
+          set_ownership "#{staged_path}/foo-#{language}"
         end
       end
     CASK

docs/Cask-Cookbook.md

@@ -670,9 +670,9 @@ Ruby `#{...}` interpolation is normally evaluated before structured steps are se
 
 `{{...}}` is not Ruby interpolation. It remains literal in the JSON API and the install-step runner expands supported tokens at install time. Use this form for install-time values inside `preflight_steps`, `postflight_steps`, `uninstall_preflight_steps` and `uninstall_postflight_steps`. When a path argument supports `base:`, `source_base:` or `target_base:`, prefer those options to embedding a path token.
 
-The runtime steps DSL retains compatibility helpers for `token`, `name`, `version`, `version.major` and `version.major_minor`. Interpolating these helpers is safe and permitted by RuboCop because they return the corresponding `{{...}}` token text rather than a concrete value. Other Ruby interpolation is rejected. Prefer explicit `{{...}}` tokens in new steps so it is clear that expansion is deferred until installation.
+The runtime steps DSL retains compatibility helpers for `token`, `name`, `arch`, `version`, `version.major` and `version.major_minor`. Interpolating these helpers is safe and permitted by RuboCop because they return the corresponding `{{...}}` token text rather than a concrete value. Other Ruby interpolation is rejected. Prefer explicit `{{...}}` tokens in new steps so it is clear that expansion is deferred until installation.
 
-Content, replacements, command arguments and command environments may use fixed install-time tokens. These include `{{HOMEBREW_BREW_FILE}}`, `{{HOMEBREW_CELLAR}}`, `{{HOMEBREW_PREFIX}}`, `{{token}}`, `{{name}}`, `{{user}}`, `{{staged_path}}`, `{{appdir}}`, `{{caskroom_path}}`, `{{temp}}`, `{{version}}`, `{{version.major}}` and `{{version.major_minor}}`. `{{name}}` is retained for compatibility; prefer `{{token}}`. Any other `{{...}}` is left verbatim. For example: `write_file "settings.conf", "application = {{appdir}}/Example.app"`.
+Content, replacements, command arguments and command environments may use fixed install-time tokens. These include `{{HOMEBREW_BREW_FILE}}`, `{{HOMEBREW_CELLAR}}`, `{{HOMEBREW_PREFIX}}`, `{{token}}`, `{{name}}`, `{{arch}}`, `{{user}}`, `{{staged_path}}`, `{{appdir}}`, `{{caskroom_path}}`, `{{temp}}`, `{{version}}`, `{{version.major}}` and `{{version.major_minor}}`. `{{name}}` is retained for compatibility; prefer `{{token}}`. `{{arch}}` expands to the value the cask's `arch` stanza selected for the current architecture, and to an empty string when the cask has no matching value. Any other `{{...}}` is left verbatim. For example: `write_file "settings.conf", "application = {{appdir}}/Example.app"`.
 
 {% endraw %}