move logic from leaves to formula

Library/Homebrew/cmd/leaves.rb

@@ -2,7 +2,6 @@
 # frozen_string_literal: true
 
 require "formula"
-require "tab"
 require "cli/parser"
 
 module Homebrew
@@ -23,9 +22,7 @@ module Homebrew
   def leaves
     leaves_args.parse
 
-    installed = Formula.installed.sort
-    deps_of_installed = installed.flat_map(&:runtime_formula_dependencies)
-    leaves = installed.map(&:full_name) - deps_of_installed.map(&:full_name)
+    leaves = Formula.installed_non_deps.map(&:full_name).sort
     leaves.each(&method(:puts))
   end
 end

Library/Homebrew/formula.rb

@@ -1515,6 +1515,18 @@ class Formula
     end.uniq(&:name)
   end
 
+  # An array of installed {Formula} that are dependencies of other installed {Formula}
+  # @private
+  def self.installed_deps(formulae=installed)
+    formulae.flat_map(&:runtime_formula_dependencies).uniq(&:name)
+  end
+
+  # An array of all installed {Formula} that are not dependencies of other installed {Formula}
+  # @private
+  def self.installed_non_deps(formulae=installed)
+    formulae - installed_deps(formulae)
+  end
+
   def self.installed_with_alias_path(alias_path)
     return [] if alias_path.nil?
 

Library/Homebrew/test/cmd/leaves_spec.rb

@@ -8,14 +8,42 @@ describe "Homebrew.leaves_args" do
 end
 
 describe "brew leaves", :integration_test do
-  it "prints all Formulae that are not dependencies of other Formulae" do
-    setup_test_formula "foo"
-    setup_test_formula "bar"
-    (HOMEBREW_CELLAR/"foo/0.1/somedir").mkpath
+  context "when there are no installed Formulae" do
+    it "prints nothing" do
+      setup_test_formula "foo"
+      setup_test_formula "bar"
       
-    expect { brew "leaves" }
-      .to output("foo\n").to_stdout
-      .and not_to_output.to_stderr
-      .and be_a_success
+      expect { brew "leaves" }
+        .to not_to_output.to_stdout
+        .and not_to_output.to_stderr
+        .and be_a_success
+    end
+  end
+
+  context "when there are only installed Formulae without dependencies" do
+    it "prints all installed Formulae" do
+      setup_test_formula "foo"
+      setup_test_formula "bar"
+      (HOMEBREW_CELLAR/"foo/0.1/somedir").mkpath
+      
+      expect { brew "leaves" }
+        .to output("foo\n").to_stdout
+        .and not_to_output.to_stderr
+        .and be_a_success
+    end
+  end
+
+  context "when there are installed Formulae" do
+    it "prints all installed Formulae that are not dependencies of another installed Formula" do
+      setup_test_formula "foo"
+      setup_test_formula "bar"
+      (HOMEBREW_CELLAR/"foo/0.1/somedir").mkpath
+      (HOMEBREW_CELLAR/"bar/0.1/somedir").mkpath
+      
+      expect { brew "leaves" }
+        .to output("bar\n").to_stdout
+        .and not_to_output.to_stderr
+        .and be_a_success
+    end
   end
 end

Library/Homebrew/test/formula_spec.rb

@@ -440,6 +440,80 @@ describe Formula do
     end
   end
 
+  describe "::installed_deps" do
+    let(:formula_is_dep) do
+      formula "foo" do
+        url "foo-1.1"
+      end
+    end
+
+    let(:formula_with_deps) do
+      formula "bar" do
+        url "bar-1.0"
+      end
+    end
+
+    let(:formulae) do
+      [
+        formula_with_deps,
+        formula_is_dep
+      ]
+    end    
+
+    before do
+      allow(formula_with_deps).to receive(:runtime_formula_dependencies).and_return([ formula_is_dep ])
+    end
+
+    specify "without formulae parameter" do
+      allow(described_class).to receive(:installed).and_return(formulae)
+
+      expect(described_class.installed_deps)
+          .to eq([formula_is_dep])
+    end
+
+    specify "with formulae parameter" do
+      expect(described_class.installed_deps(formulae))
+          .to eq([formula_is_dep])
+    end
+  end
+
+  describe "::installed_non_deps" do
+    let(:formula_is_dep) do
+      formula "foo" do
+        url "foo-1.1"
+      end
+    end
+
+    let(:formula_with_deps) do
+      formula "bar" do
+        url "bar-1.0"
+      end
+    end
+
+    let(:formulae) do
+      [
+        formula_with_deps,
+        formula_is_dep
+      ]
+    end
+
+    before do
+      allow(formula_with_deps).to receive(:runtime_formula_dependencies).and_return([ formula_is_dep ])
+    end
+
+    specify "without formulae parameter" do
+      allow(described_class).to receive(:installed).and_return(formulae)
+
+      expect(described_class.installed_non_deps)
+          .to eq([formula_with_deps])
+    end
+
+    specify "with formulae parameter" do
+      expect(described_class.installed_non_deps(formulae))
+          .to eq([formula_with_deps])
+    end
+  end
+
   describe "::installed_with_alias_path" do
     specify "with alias path with nil" do
       expect(described_class.installed_with_alias_path(nil)).to be_empty