style: don't use prefix + directory

Library/Homebrew/dev-cmd/audit.rb

@@ -843,15 +843,6 @@ module Homebrew
         problem "Don't need to interpolate \"#{Regexp.last_match(2)}\" with #{Regexp.last_match(1)}"
       end
 
-      # Prefer formula path shortcuts in Pathname+
-      if line =~ %r{\(\s*(prefix\s*\+\s*(['"])(bin|include|libexec|lib|sbin|share|Frameworks)[/'"])}
-        # TODO: check could be in RuboCop
-        problem(
-          "\"(#{Regexp.last_match(1)}...#{Regexp.last_match(2)})\" should" \
-          " be \"(#{Regexp.last_match(3).downcase}+...)\"",
-        )
-      end
-
       return unless @strict
 
       # TODO: check could be in RuboCop

Library/Homebrew/rubocops/text.rb

@@ -93,6 +93,19 @@ module RuboCop
             offending_node(n)
             problem "Use `depends_on :java` to set JAVA_HOME"
           end
+
+          find_strings(body_node).each do |n|
+            # Skip strings that don't start with one of the keywords
+            next unless regex_match_group(n, %r{^(bin|include|libexec|lib|sbin|share|Frameworks)/?})
+
+            parent = n.parent
+            # Only look at keywords that have `prefix` before them
+            prefix_keyword_regex = %r{(prefix\s*\+\s*["'](bin|include|libexec|lib|sbin|share|Frameworks))["'/]}
+            if match = parent.source.match(prefix_keyword_regex)
+              offending_node(parent)
+              problem "Use `#{match[2].downcase}` instead of `#{match[1]}\"`"
+            end
+          end
         end
       end
     end

Library/Homebrew/test/rubocops/text_spec.rb

@@ -292,6 +292,28 @@ describe RuboCop::Cop::FormulaAudit::Text do
         end
       RUBY
     end
+
+    it "When using `prefix + \"bin\"` instead of `bin`" do
+      expect_offense(<<~RUBY)
+        class Foo < Formula
+          def install
+            ohai prefix + "bin"
+                 ^^^^^^^^^^^^^^ Use `bin` instead of `prefix + "bin"`
+          end
+        end
+      RUBY
+    end
+
+    it "When using `prefix + \"bin/foo\"` instead of `bin`" do
+      expect_offense(<<~RUBY)
+        class Foo < Formula
+          def install
+            ohai prefix + "bin/foo"
+                 ^^^^^^^^^^^^^^^^^^ Use `bin` instead of `prefix + "bin"`
+          end
+        end
+      RUBY
+    end
   end
 end