linkage_checker: check for extraneous dependencies

Library/Homebrew/os/mac/linkage_checker.rb

@@ -5,7 +5,7 @@ require "formula"
 class LinkageChecker
   attr_reader :keg, :formula
   attr_reader :brewed_dylibs, :system_dylibs, :broken_dylibs, :variable_dylibs
-  attr_reader :undeclared_deps, :reverse_links
+  attr_reader :undeclared_deps, :extraneous_deps, :reverse_links
 
   def initialize(keg, formula = nil)
     @keg = keg
@@ -16,6 +16,7 @@ class LinkageChecker
     @variable_dylibs = Set.new
     @undeclared_deps = []
     @reverse_links = Hash.new { |h, k| h[k] = Set.new }
+    @extraneous_deps = []
     check_dylibs
   end
 
@@ -51,7 +52,7 @@ class LinkageChecker
       end
     end
 
-    @undeclared_deps = check_undeclared_deps if formula
+    @undeclared_deps, @extraneous_deps = check_undeclared_deps if formula
   end
 
   def check_undeclared_deps
@@ -77,6 +78,11 @@ class LinkageChecker
         a <=> b
       end
     end
+    extraneous_deps = declared_dep_names.reject do |full_name|
+        name = full_name.split("/").last
+        @brewed_dylibs.keys.map{ |x| x.split("/").last }.include? name
+    end
+    return undeclared_deps, extraneous_deps
   end
 
   def display_normal_output
@@ -85,6 +91,7 @@ class LinkageChecker
     display_items "Variable-referenced libraries", @variable_dylibs
     display_items "Missing libraries", @broken_dylibs
     display_items "Possible undeclared dependencies", @undeclared_deps
+    display_items "Possible extraneous dependencies", @extraneous_deps
   end
 
   def display_reverse_output
@@ -113,6 +120,10 @@ class LinkageChecker
     !@undeclared_deps.empty?
   end
 
+  def extraneous_deps?
+    !@extraneous_deps.empty?
+  end
+
   private
 
   # Whether or not dylib is a harmless broken link, meaning that it's