defines Module#qualified_const_(defined?|get|set) and String#deconstantize

This commit also implements a faster version of #demodulize I was unable
to isolate with git add --patch.

Not a big fan of the name #deconstantize. It complements #demodulize
getting rid of the rightmost constant, hence the name, but it is
unrelated to the well-known #constantize. So unsure. Could not come
with anything better, please feel free to rename.

1 files changed, 94 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/module/qualified_const_test.rb b/activesupport/test/core_ext/module/qualified_const_test.rb
new file mode 100644
index 0000000000..8af0b9a023
--- /dev/null
+++ b/activesupport/test/core_ext/module/qualified_const_test.rb
@@ -0,0 +1,94 @@
+require 'abstract_unit'
+require 'active_support/core_ext/module/qualified_const'
+
+module QualifiedConstTestMod
+  X = false
+
+  module M
+    X = 1
+
+    class C
+      X = 2
+    end
+  end
+
+  module N
+    include M
+  end
+end
+
+class QualifiedConstTest < ActiveSupport::TestCase
+  test "Object.qualified_const_defined?" do
+    assert Object.qualified_const_defined?("QualifiedConstTestMod")
+    assert !Object.qualified_const_defined?("NonExistingQualifiedConstTestMod")
+
+    assert Object.qualified_const_defined?("QualifiedConstTestMod::X")
+    assert !Object.qualified_const_defined?("QualifiedConstTestMod::Y")
+
+    assert Object.qualified_const_defined?("QualifiedConstTestMod::M::X")
+    assert !Object.qualified_const_defined?("QualifiedConstTestMod::M::Y")
+
+    if Module.method(:const_defined?).arity == 1
+      assert !Object.qualified_const_defined?("QualifiedConstTestMod::N::X")
+    else
+      assert Object.qualified_const_defined?("QualifiedConstTestMod::N::X")
+      assert !Object.qualified_const_defined?("QualifiedConstTestMod::N::X", false)
+      assert Object.qualified_const_defined?("QualifiedConstTestMod::N::X", true)
+    end
+  end
+
+  test "mod.qualified_const_defined?" do
+    assert QualifiedConstTestMod.qualified_const_defined?("M")
+    assert !QualifiedConstTestMod.qualified_const_defined?("NonExistingM")
+
+    assert QualifiedConstTestMod.qualified_const_defined?("M::X")
+    assert !QualifiedConstTestMod.qualified_const_defined?("M::Y")
+
+    assert QualifiedConstTestMod.qualified_const_defined?("M::C::X")
+    assert !QualifiedConstTestMod.qualified_const_defined?("M::C::Y")
+
+    if Module.method(:const_defined?).arity == 1
+      assert !QualifiedConstTestMod.qualified_const_defined?("QualifiedConstTestMod::N::X")
+    else
+      assert QualifiedConstTestMod.qualified_const_defined?("N::X")
+      assert !QualifiedConstTestMod.qualified_const_defined?("N::X", false)
+      assert QualifiedConstTestMod.qualified_const_defined?("N::X", true)
+    end
+  end
+
+  test "qualified_const_get" do
+    assert_equal false, Object.qualified_const_get("QualifiedConstTestMod::X")
+    assert_equal false, QualifiedConstTestMod.qualified_const_get("X")
+    assert_equal 1, QualifiedConstTestMod.qualified_const_get("M::X")
+    assert_equal 1, QualifiedConstTestMod.qualified_const_get("N::X")
+    assert_equal 2, QualifiedConstTestMod.qualified_const_get("M::C::X")
+
+    assert_raise(NameError) { QualifiedConstTestMod.qualified_const_get("M::C::Y")}
+  end
+
+  test "qualified_const_set" do
+    m = Module.new
+    assert_equal m, Object.qualified_const_set("QualifiedConstTestMod2", m)
+    assert_equal m, ::QualifiedConstTestMod2
+
+    # We are going to assign to existing constants on purpose, so silence warnings.
+    silence_warnings do
+      assert_equal true, QualifiedConstTestMod.qualified_const_set("QualifiedConstTestMod::X", true)
+      assert_equal true, QualifiedConstTestMod::X
+
+      assert_equal 10, QualifiedConstTestMod::M.qualified_const_set("X", 10)
+      assert_equal 10, QualifiedConstTestMod::M::X
+    end
+  end
+
+  test "reject absolute paths" do
+    assert_raise(NameError, "wrong constant name ::X") { Object.qualified_const_defined?("::X")}
+    assert_raise(NameError, "wrong constant name ::X") { Object.qualified_const_defined?("::X::Y")}
+
+    assert_raise(NameError, "wrong constant name ::X") { Object.qualified_const_get("::X")}
+    assert_raise(NameError, "wrong constant name ::X") { Object.qualified_const_get("::X::Y")}
+
+    assert_raise(NameError, "wrong constant name ::X") { Object.qualified_const_set("::X", nil)}
+    assert_raise(NameError, "wrong constant name ::X") { Object.qualified_const_set("::X::Y", nil)}
+  end
+end