Widen attestation verification rollout

Take 2 of #17692 but with:

- provide and document `HOMEBREW_NO_VERIFY_ATTESTATIONS`
- don't try to run unless there's GitHub credentials
- don't try to run unless `gh` is installed
- don't try to run in CI

While we're here:
- split out a `Homebrew::EnvConfig.devcmdrun?` helper method
- add some missing `Homebrew::EnvConfig.github_api_token` presence
  checks

Library/Homebrew/attestation.rb

@@ -45,13 +45,13 @@ class GhAuthNeeded < RuntimeError; end
     # @api private
     sig { returns(T::Boolean) }
     def self.enabled?
-      # TODO: allow this undocumented variable until this is rolled out more
-      #       widely and then we can remove or document it.
-      return false if ENV.fetch("HOMEBREW_NO_VERIFY_ATTESTATIONS", false)
+      return false if Homebrew::EnvConfig.no_verify_attestations?
       return true if Homebrew::EnvConfig.verify_attestations?
+      return false if GitHub::API.credentials.blank?
       return false if ENV.fetch("CI", false)
+      return false unless Formula["gh"].any_version_installed?
 
-      Homebrew::EnvConfig.developer?
+      Homebrew::EnvConfig.developer? || Homebrew::EnvConfig.devcmdrun?
     end
 
     # Returns a path to a suitable `gh` executable for attestation verification.

Library/Homebrew/cmd/developer.rb

@@ -36,7 +36,7 @@ def run
           if env_vars.any?
             verb = (env_vars.count == 1) ? "is" : "are"
             puts "Developer mode is enabled because #{env_vars.to_sentence} #{verb} set."
-          elsif Homebrew::Settings.read("devcmdrun") == "true"
+          elsif Homebrew::EnvConfig.devcmdrun?
             puts "Developer mode is enabled."
           else
             puts "Developer mode is disabled."

Library/Homebrew/diagnostic.rb

@@ -865,7 +865,7 @@ def check_deleted_formula
       def check_for_unnecessary_core_tap
         return if Homebrew::EnvConfig.developer?
         return if Homebrew::EnvConfig.no_install_from_api?
-        return if Homebrew::Settings.read("devcmdrun") == "true"
+        return if Homebrew::EnvConfig.devcmdrun?
         return unless CoreTap.instance.installed?
 
         <<~EOS
@@ -879,7 +879,7 @@ def check_for_unnecessary_core_tap
       def check_for_unnecessary_cask_tap
         return if Homebrew::EnvConfig.developer?
         return if Homebrew::EnvConfig.no_install_from_api?
-        return if Homebrew::Settings.read("devcmdrun") == "true"
+        return if Homebrew::EnvConfig.devcmdrun?
 
         cask_tap = CoreCaskTap.instance
         return unless cask_tap.installed?

Library/Homebrew/env_config.rb

@@ -379,6 +379,11 @@ module EnvConfig
         description: "If set, `brew update` will not show the list of newly added formulae/casks.",
         boolean:     true,
       },
+      HOMEBREW_NO_VERIFY_ATTESTATIONS:           {
+        description: "If set, Homebrew not verify cryptographic attestations of build provenance for bottles " \
+                     "from homebrew-core.",
+        boolean:     true,
+      },
       HOMEBREW_PIP_INDEX_URL:                    {
         description:  "If set, `brew install` <formula> will use this URL to download PyPI package resources.",
         default_text: "`https://pypi.org/simple`.",
@@ -556,5 +561,10 @@ def cask_opts_require_sha?
     def automatically_set_no_install_from_api?
       ENV["HOMEBREW_AUTOMATICALLY_SET_NO_INSTALL_FROM_API"].present?
     end
+
+    sig { returns(T::Boolean) }
+    def devcmdrun?
+      Homebrew::Settings.read("devcmdrun") == "true"
+    end
   end
 end

Library/Homebrew/utils/analytics.rb

@@ -119,7 +119,7 @@ def report_command_run(command_instance)
         tags = {
           command:,
           ci:        ENV["CI"].present?,
-          devcmdrun: config_true?(:devcmdrun),
+          devcmdrun: Homebrew::EnvConfig.devcmdrun?,
           developer: Homebrew::EnvConfig.developer?,
         }
 
@@ -354,7 +354,7 @@ def default_package_tags
             prefix:,
             default_prefix: Homebrew.default_prefix?,
             developer:      Homebrew::EnvConfig.developer?,
-            devcmdrun:      config_true?(:devcmdrun),
+            devcmdrun:      Homebrew::EnvConfig.devcmdrun?,
             arch:           HOMEBREW_PHYSICAL_PROCESSOR,
             os:             HOMEBREW_SYSTEM,
           }

Library/Homebrew/utils/curl.rb

@@ -352,7 +352,7 @@ def curl_check_http_content(url, url_type, specs: {}, user_agents: [:default], r
         check_github_api = url_type == SharedAudits::URL_TYPE_HOMEPAGE &&
                            details[:status_code] == "404" &&
                            repo_details &&
-                           Homebrew::EnvConfig.github_api_token
+                           Homebrew::EnvConfig.github_api_token.present?
 
         unless check_github_api
           return "The #{url_type} #{url} is not reachable (HTTP status code #{details[:status_code]})"

Library/Homebrew/utils/github/api.rb

@@ -181,7 +181,9 @@ def self.keychain_username_password
     end
 
     def self.credentials
-      @credentials ||= Homebrew::EnvConfig.github_api_token || github_cli_token || keychain_username_password
+      @credentials ||= Homebrew::EnvConfig.github_api_token.presence
+      @credentials ||= github_cli_token.presence
+      @credentials ||= keychain_username_password.presence
     end
 
     sig { returns(Symbol) }