keg: don't rely on #to_formula

It doesn't always work.
For example, a keg could have been installed with a formula from a
URL, which Homebrew now does not know how to access.

Fixes #1496.

1 files changed, 17 insertions, 2 deletions

diff --git a/Library/Homebrew/test/test_keg.rb b/Library/Homebrew/test/test_keg.rb
index 7450d9c0f..fdc739c9d 100644
--- a/Library/Homebrew/test/test_keg.rb
+++ b/Library/Homebrew/test/test_keg.rb
@@ -317,12 +317,16 @@ end
 
 class InstalledDependantsTests < LinkTests
   def stub_formula_name(name)
-    stub_formula_loader formula(name) { url "foo-1.0" }
+    f = formula(name) { url "foo-1.0" }
+    stub_formula_loader f
+    stub_formula_loader f, "homebrew/core/#{f}"
+    f
   end
 
   def setup_test_keg(name, version)
-    stub_formula_name(name)
+    f = stub_formula_name(name)
     keg = super
+    Tab.create(f, DevelopmentTools.default_compiler, :libcxx).write
     Formula.clear_cache
     keg
   end
@@ -345,6 +349,17 @@ class InstalledDependantsTests < LinkTests
     end
   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.
+  def test_unknown_formula
+    Formulary.unstub(:loader_for)
+    dependencies []
+    alter_tab { |t| t.source["path"] = nil }
+    assert_empty @keg.installed_dependents
+    assert_nil Keg.find_some_installed_dependents([@keg])
+  end
+
   def test_no_dependencies_anywhere
     dependencies nil
     assert_empty @keg.installed_dependents