Add MPICH cop and test

 - Split off from PR Homebrew/brew#6209
 - Create stand alone class for cop w/ auto-correct

Library/Homebrew/rubocops/lines.rb

@@ -157,6 +157,24 @@ module RuboCop
         end
       end
 
+      class MpiCheck < FormulaCop
+        def audit_formula(_node, _class_node, _parent_class_node, body_node)
+          # Enforce use of OpenMPI for MPI dependency in core
+          return unless formula_tap == "homebrew-core"
+
+          find_method_with_args(body_node, :depends_on, "mpich") do
+            problem "Use 'depends_on \"open-mpi\"' instead of '#{@offensive_node.source}'."
+          end
+        end
+
+        def autocorrect(node)
+          # The dependency nodes may need to be re-sorted because of this
+          lambda do |corrector|
+            corrector.replace(node.source_range, "depends_on \"open-mpi\"")
+          end
+        end
+      end
+
       class Miscellaneous < FormulaCop
         def audit_formula(_node, _class_node, _parent_class_node, body_node)
           # FileUtils is included in Formula

Library/Homebrew/test/rubocops/lines_spec.rb

@@ -279,6 +279,23 @@ describe RuboCop::Cop::FormulaAudit::OptionDeclarations do
   end
 end
 
+describe RuboCop::Cop::FormulaAudit::MpiCheck do
+  subject(:cop) { described_class.new }
+
+  context "When auditing formula" do
+    it "reports an offense when using depends_on \"mpich\"" do
+      expect_offense(<<~RUBY, "/homebrew-core/")
+        class Foo < Formula
+          desc "foo"
+          url 'https://brew.sh/foo-1.0.tgz'
+          depends_on "mpich"
+          ^^^^^^^^^^^^^^^^^^ Use 'depends_on "open-mpi"' instead of 'depends_on "mpich"'.
+        end
+      RUBY
+    end
+  end
+end
+
 describe RuboCop::Cop::FormulaAudit::Miscellaneous do
   subject(:cop) { described_class.new }