audit: disallow capitalization and period in conflicts_with reason

Library/Homebrew/rubocops/conflicts.rb

@@ -15,11 +15,40 @@ module RuboCop
           bash-completion@2
         ].freeze
 
-        def audit_formula(_node, _class_node, _parent_class_node, body)
+        def audit_formula(_node, _class_node, _parent_class_node, body_node)
+          find_method_calls_by_name(body_node, :conflicts_with).each do |conflicts_with_call|
+            next unless parameters(conflicts_with_call).last.respond_to? :values
+
+            reason = parameters(conflicts_with_call).last.values.first
+            offending_node(reason)
+            name = Regexp.new(@formula_name, Regexp::IGNORECASE)
+            reason = string_content(reason).sub(name, "")
+            first_word = reason.split.first
+
+            if reason.match?(/\A[A-Z]/)
+              problem "'#{first_word}' from the `conflicts_with` reason should be '#{first_word.downcase}'."
+            end
+
+            problem "`conflicts_with` reason should not end with a period." if reason.end_with?(".")
+          end
+
           return unless versioned_formula?
 
           problem MSG if !ALLOWLIST.include?(@formula_name) &&
-                         method_called_ever?(body, :conflicts_with)
+                         method_called_ever?(body_node, :conflicts_with)
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            if versioned_formula?
+              corrector.replace(node.source_range, "keg_only :versioned_formula")
+            else
+              reason = string_content(node)
+              reason[0] = reason[0].downcase
+              reason = reason.delete_suffix(".")
+              corrector.replace(node.source_range, "\"#{reason}\"")
+            end
+          end
         end
       end
     end

Library/Homebrew/test/rubocops/conflicts_spec.rb

@@ -5,14 +5,34 @@ require "rubocops/conflicts"
 describe RuboCop::Cop::FormulaAudit::Conflicts do
   subject(:cop) { described_class.new }
 
-  context "When auditing formula for conflicts with" do
-    it "multiple conflicts_with" do
+  context "When auditing conflicts_with" do
+    it "conflicts_with reason is capitalized" do
+      expect_offense(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+        class Foo < Formula
+          url "https://brew.sh/foo-1.0.tgz"
+          conflicts_with "bar", :because => "Reason"
+                                            ^^^^^^^^ 'Reason' from the `conflicts_with` reason should be 'reason'.
+          conflicts_with "baz", :because => "Foo is the formula name which does not require downcasing"
+        end
+      RUBY
+    end
+
+    it "conflicts_with reason ends with a period" do
+      expect_offense(<<~RUBY)
+        class Foo < Formula
+          url "https://brew.sh/foo-1.0.tgz"
+          conflicts_with "bar", "baz", :because => "reason."
+                                                   ^^^^^^^^^ `conflicts_with` reason should not end with a period.
+        end
+      RUBY
+    end
+
+    it "conflicts_with in a versioned formula" do
       expect_offense(<<~RUBY, "/homebrew-core/Formula/foo@2.0.rb")
         class FooAT20 < Formula
           url 'https://brew.sh/foo-2.0.tgz'
-          conflicts_with "mysql", "mariadb", "percona-server",
-          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Versioned formulae should not use `conflicts_with`. Use `keg_only :versioned_formula` instead.
-                           :because => "both install plugins"
+          conflicts_with "mysql", "mariadb"
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Versioned formulae should not use `conflicts_with`. Use `keg_only :versioned_formula` instead.
         end
       RUBY
     end
@@ -21,10 +41,48 @@ describe RuboCop::Cop::FormulaAudit::Conflicts do
       expect_no_offenses(<<~RUBY, "/homebrew-core/Formula/foo@2.0.rb")
         class FooAT20 < Formula
           url 'https://brew.sh/foo-2.0.tgz'
-          desc 'Bar'
+          homepage "https://brew.sh"
         end
       RUBY
     end
+
+    it "auto-corrects capitalized reason" do
+      source = <<~RUBY
+        class Foo < Formula
+          url "https://brew.sh/foo-1.0.tgz"
+          conflicts_with "bar", :because => "Reason"
+        end
+      RUBY
+
+      corrected_source = <<~RUBY
+        class Foo < Formula
+          url "https://brew.sh/foo-1.0.tgz"
+          conflicts_with "bar", :because => "reason"
+        end
+      RUBY
+
+      new_source = autocorrect_source(source)
+      expect(new_source).to eq(corrected_source)
+    end
+
+    it "auto-corrects trailing period" do
+      source = <<~RUBY
+        class Foo < Formula
+          url "https://brew.sh/foo-1.0.tgz"
+          conflicts_with "bar", :because => "reason."
+        end
+      RUBY
+
+      corrected_source = <<~RUBY
+        class Foo < Formula
+          url "https://brew.sh/foo-1.0.tgz"
+          conflicts_with "bar", :because => "reason"
+        end
+      RUBY
+
+      new_source = autocorrect_source(source)
+      expect(new_source).to eq(corrected_source)
+    end
   end
 
   include_examples "formulae exist", described_class::ALLOWLIST