update-report: better handle user set bottle domain, core git remote.

Unset these variables and print a warning if they were set to
non-default values.

Library/Homebrew/cmd/update-report.rb

@@ -44,12 +44,32 @@ module Homebrew
 
     # Run `brew update` (again) if we've got a linuxbrew-core CoreTap
     if CoreTap.instance.linuxbrew_core? && ENV["HOMEBREW_LINUXBREW_CORE_MIGRATION"].blank?
+      ohai_stdout_or_stderr "Re-running `brew update` for linuxbrew-core migration"
+
+      if ENV["HOMEBREW_CORE_DEFAULT_GIT_REMOTE"] != ENV["HOMEBREW_CORE_GIT_REMOTE"]
+        opoo <<~EOS
+          HOMEBREW_CORE_GIT_REMOTE was set. It has been unset for the migration.
+          You may need to change this from a linuxbrew-core mirror to a homebrew-core one.
+
+        EOS
+      end
+      ENV.delete("HOMEBREW_CORE_GIT_REMOTE")
+
+      if ENV["HOMEBREW_BOTTLE_DEFAULT_DOMAIN"] != ENV["HOMEBREW_BOTTLE_DOMAIN"]
+        opoo <<~EOS
+          HOMEBREW_BOTTLE_DOMAIN was set. It has been unset for the migration.
+          You may need to change this Linuxbrew packages to Homebrew packages.
+
+        EOS
+      end
+      ENV.delete("HOMEBREW_BOTTLE_DOMAIN")
+
       ENV["HOMEBREW_LINUXBREW_CORE_MIGRATION"] = "1"
+      FileUtils.rm_f HOMEBREW_LOCKS/"update"
+
       update_args = []
       update_args << "--preinstall" if args.preinstall?
       update_args << "--force" if args.force?
-      ohai_stdout_or_stderr "Re-running `brew update` for linuxbrew-core migration"
-      FileUtils.rm_f HOMEBREW_LOCKS/"update"
       exec HOMEBREW_BREW_FILE, "update", *update_args
     end
 

Library/Homebrew/extend/os/linux/diagnostic.rb

@@ -16,6 +16,7 @@ module Homebrew
         %w[
           check_access_directories
           check_linuxbrew_core
+          check_linuxbrew_bottle_domain
         ].freeze
       end
 
@@ -127,6 +128,16 @@ module Homebrew
           You must `brew update` to update to homebrew-core.
         EOS
       end
+
+      def check_linuxbrew_bottle_domain
+        return unless Homebrew::EnvConfig.bottle_domain.include?("linuxbrew-core")
+
+        <<~EOS
+          Your HOMEBREW_BOTTLE_DOMAIN still contains linuxbrew-core.
+          You must unset it (or adjust it to not contain linuxbrew-core
+          e.g. by using homebrew-core instead).
+        EOS
+      end
     end
   end
 end