bottle: make bottle checksums reproducible.

I've set all the variable data to versions that are dependent on the
latest source file date and various modification dates also to the
latest source file date. With this if you rerun `brew bottle`
multiple times in a row you will see the same checksum even if you have
`brew reinstall`ed (as long as upstream does not hardcode e.g. the
build date).

I debugged this with diffoscope and worked on this as part of the
Athens 2015 reproducible builds workshop:
https://reproducible-builds.org/events/athens2015/

Closes Homebrew/homebrew#46587.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/cmd/bottle.rb

@@ -174,6 +174,9 @@ module Homebrew
     filename = Bottle::Filename.create(f, bottle_tag, bottle_revision)
     bottle_path = Pathname.pwd/filename
 
+    tar_filename = filename.to_s.sub(/.gz$/, "")
+    tar_path = Pathname.pwd/tar_filename
+
     prefix = HOMEBREW_PREFIX.to_s
     cellar = HOMEBREW_CELLAR.to_s
 
@@ -183,7 +186,13 @@ module Homebrew
     relocatable = false
     skip_relocation = false
 
+    formula_source_time = f.stable.stage do
+      Pathname.pwd.to_enum(:find).map(&:mtime).max
+    end
+
     keg.lock do
+      original_tab = nil
+
       begin
         keg.relocate_install_names prefix, Keg::PREFIX_PLACEHOLDER,
           cellar, Keg::CELLAR_PLACEHOLDER
@@ -192,10 +201,25 @@ module Homebrew
 
         keg.delete_pyc_files!
 
+        tab = Tab.for_keg(keg)
+        original_tab = tab.dup
+        empty_tab = Tab.empty
+        tab["poured_from_bottle"] = empty_tab["poured_from_bottle"]
+        tab["HEAD"] = empty_tab["HEAD"]
+        tab["time"] = empty_tab["time"]
+        tab.write
+
+        keg.find {|k| File.utime(File.atime(k), formula_source_time, k) }
+
         cd cellar do
+          safe_system "tar", "cf", tar_path, "#{f.name}/#{f.pkg_version}"
+          File.utime(File.atime(tar_path), formula_source_time, tar_path)
+          relocatable_tar_path = "#{f}-bottle.tar"
+          mv tar_path, relocatable_tar_path
           # Use gzip, faster to compress than bzip2, faster to uncompress than bzip2
           # or an uncompressed tarball (and more bandwidth friendly).
-          safe_system "tar", "czf", bottle_path, "#{f.name}/#{f.pkg_version}"
+          safe_system "gzip", "-f", relocatable_tar_path
+          mv "#{relocatable_tar_path}.gz", bottle_path
         end
 
         if bottle_path.size > 1*1024*1024
@@ -222,6 +246,7 @@ module Homebrew
         raise
       ensure
         ignore_interrupts do
+          original_tab.write
           keg.relocate_install_names Keg::PREFIX_PLACEHOLDER, prefix,
             Keg::CELLAR_PLACEHOLDER, cellar
         end

Library/Homebrew/formula_installer.rb

@@ -741,6 +741,8 @@ class FormulaInstaller
 
     tab.tap = formula.tap
     tab.poured_from_bottle = true
+    tab.time = Time.now.to_i
+    tab.head = Homebrew.git_head
     tab.write
   end