More update tweaks

- Make copying to `*_names.before.txt` the responsibility of `update.sh`
  (unless the file doesn't exist at all). This provides the added
  benefit of allowing the inspection of the before/after state after
  running a `brew update` rather than both files always being identical
  at this point.
- State `No changes to formulae or casks.` on macOS.
- Rename and flip `updated_formula_report` to `auto_update`; this naming
  was confusing every time.
- Only display the `You can upgrade with...` messaging if we're not
  auto-updating as sometimes it will be displayed before the commands it
  references (e.g. `upgrade`, `outdated` or an `install` that proceeds
  to upgrade these formulae).

Fixes https://github.com/Homebrew/brew/issues/15065

Library/Homebrew/cmd/update-report.rb

@@ -225,11 +225,11 @@ module Homebrew
             updated_taps << tap.name
             hub.add(reporter, auto_update: args.auto_update?)
           end
-        end
+        else
-
           FileUtils.cp names_txt, names_before_txt
         end
       end
+    end
 
     unless updated_taps.empty?
       auto_update_header args: args
@@ -239,14 +239,14 @@ module Homebrew
 
     if updated
       if hub.empty?
-        puts "No changes to formulae." unless args.quiet?
+        puts no_changes_message unless args.quiet?
       else
         if ENV.fetch("HOMEBREW_UPDATE_REPORT_ONLY_INSTALLED", false)
           opoo "HOMEBREW_UPDATE_REPORT_ONLY_INSTALLED is now the default behaviour, " \
                "so you can unset it from your environment."
         end
 
-        hub.dump(updated_formula_report: !args.auto_update?) unless args.quiet?
+        hub.dump(auto_update: args.auto_update?) unless args.quiet?
         hub.reporters.each(&:migrate_tap_migration)
         hub.reporters.each { |r| r.migrate_formula_rename(force: args.force?, verbose: args.verbose?) }
 
@@ -303,6 +303,10 @@ module Homebrew
     EOS
   end
 
+  def no_changes_message
+    "No changes to formulae or casks."
+  end
+
   def shorten_revision(revision)
     Utils.popen_read("git", "-C", HOMEBREW_REPOSITORY, "rev-parse", "--short", revision).chomp
   end
@@ -627,7 +631,7 @@ class ReporterHub
 
   delegate empty?: :@hash
 
-  def dump(updated_formula_report: true)
+  def dump(auto_update: false)
     report_all = ENV["HOMEBREW_UPDATE_REPORT_ALL_FORMULAE"].present?
     if report_all && !Homebrew::EnvConfig.no_install_from_api?
       odeprecated "HOMEBREW_UPDATE_REPORT_ALL_FORMULAE"
@@ -644,10 +648,10 @@ class ReporterHub
     outdated_formulae = []
     outdated_casks = []
 
-    if updated_formula_report && report_all
+    if !auto_update && report_all
       dump_modified_formula_report
       dump_modified_cask_report
-    elsif updated_formula_report
+    elsif !auto_update
       outdated_formulae = Formula.installed.select(&:outdated?).map(&:name)
       output_dump_formula_or_cask_report "Outdated Formulae", outdated_formulae
 
@@ -695,6 +699,12 @@ class ReporterHub
     puts
     puts <<~EOS
       You have #{msg} installed.
+    EOS
+    # If we're auto-updating, don't need to suggest commands that we're perhaps
+    # already running.
+    return if auto_update
+
+    puts <<~EOS
       You can upgrade #{update_pronoun} with #{Tty.bold}brew upgrade#{Tty.reset}
       or list #{update_pronoun} with #{Tty.bold}brew outdated#{Tty.reset}.
     EOS

Library/Homebrew/cmd/update.sh

@@ -811,7 +811,12 @@ EOS
         CURRENT_JSON_BYTESIZE="$(wc -c "${HOMEBREW_CACHE}"/api/"${formula_or_cask}".jws.json)"
         if [[ "${INITIAL_JSON_BYTESIZE}" != "${CURRENT_JSON_BYTESIZE}" ]]
         then
-          rm -f "${HOMEBREW_CACHE}/api/${formula_or_cask}_names.txt"
+          if [[ -f "${HOMEBREW_CACHE}/api/${formula_or_cask}_names.txt" ]]
+          then
+            mv -f "${HOMEBREW_CACHE}/api/${formula_or_cask}_names.txt" \
+              "${HOMEBREW_CACHE}/api/${formula_or_cask}_names.before.txt"
+          fi
+
           if [[ "${formula_or_cask}" == "formula" ]]
           then
             rm -f "${HOMEBREW_CACHE}/api/formula_aliases.txt"

Library/Homebrew/extend/os/linux/cmd/update-report.rb

@@ -6,6 +6,10 @@ module Homebrew
 
   module_function
 
+  def no_changes_message
+    "No changes to formulae."
+  end
+
   def migrate_gcc_dependents_if_needed
     return if Settings.read("gcc-rpaths.fixed") == "true"