keg: fall back for dependencies of buggy tabs

Fixes #1554.

Library/Homebrew/keg.rb

@@ -104,8 +104,10 @@ class Keg
     # so need them to be calculated now.
     #
     # This happens after the initial dependency check because it's sloooow.
-    remaining_formulae = Formula.installed.select do |f|
-      f.installed_kegs.any? { |k| Tab.for_keg(k).runtime_dependencies.nil? }
+    remaining_formulae = Formula.installed.reject do |f|
+      f.installed_kegs.all? do |k|
+        Tab.for_keg(k).reliable_runtime_dependencies?
+      end
     end
 
     keg_names = kegs.map(&:name)
@@ -360,7 +362,7 @@ class Keg
     tap = Tab.for_keg(self).source["tap"]
     Keg.all.select do |keg|
       tab = Tab.for_keg(keg)
-      next if tab.runtime_dependencies.nil? # no dependency information saved.
+      next unless tab.reliable_runtime_dependencies?
       tab.runtime_dependencies.any? do |dep|
         # Resolve formula rather than directly comparing names
         # in case of conflicts between formulae from different taps.

Library/Homebrew/test/keg_test.rb

@@ -348,13 +348,18 @@ class InstalledDependantsTests < LinkTestCase
     tab.write
   end
 
-  def dependencies(deps)
+  def dependencies(deps, homebrew_version: "1.1.6")
     alter_tab do |tab|
+      tab.homebrew_version = homebrew_version
       tab.tabfile = @dependent.join("INSTALL_RECEIPT.json")
       tab.runtime_dependencies = deps
     end
   end
 
+  def unreliable_dependencies(deps)
+    dependencies(deps, homebrew_version: "1.1.5")
+  end
+
   # Test with a keg whose formula isn't known.
   # This can happen if e.g. a formula is installed
   # from a file path or URL.
@@ -406,4 +411,11 @@ class InstalledDependantsTests < LinkTestCase
     assert_equal [@dependent], @keg.installed_dependents
     assert_equal [[@keg], ["bar 1.0"]], Keg.find_some_installed_dependents([@keg])
   end
+
+  def test_fallback_for_old_versions
+    unreliable_dependencies [{ "full_name" => "baz", "version" => "1.0" }]
+    Formula["bar"].class.depends_on "foo"
+    assert_empty @keg.installed_dependents
+    assert_equal [[@keg], ["bar"]], Keg.find_some_installed_dependents([@keg])
+  end
 end

Library/Homebrew/test/uninstall_test.rb

@@ -12,6 +12,7 @@ class UninstallTests < Homebrew::TestCase
     [@dependency, @dependent].each { |f| f.installed_prefix.mkpath }
 
     tab = Tab.empty
+    tab.homebrew_version = "1.1.6"
     tab.tabfile = @dependent.installed_prefix/Tab::FILENAME
     tab.runtime_dependencies = [
       { "full_name" => "dependency", "version" => "1" },