Only optimize for the core tap

Library/Homebrew/missing_formula.rb

@@ -154,6 +154,8 @@ module Homebrew
             end
           end
 
+          # Optimization for the core tap which has many monthly commits
+          if tap.core_tap?
             # Check if the formula has been deleted in the last month.
             diff_command = ["git", "diff", "--diff-filter=D", "--name-only",
                             "@{'1 month ago'}", "--", relative_path]
@@ -163,6 +165,7 @@ module Homebrew
               ofail "No previously deleted formula found." unless silent
               return
             end
+          end
 
           # Find commit where formula was deleted in the last month.
           log_command = "git log --since='1 month ago' --diff-filter=D " \

Library/Homebrew/test/missing_formula_spec.rb

@@ -75,6 +75,7 @@ describe Homebrew::MissingFormula do
       end
     end
 
+    shared_examples "it detects deleted formulae" do
       context "with a deleted formula" do
         let(:formula) { "homebrew/foo/deleted-formula" }
 
@@ -88,6 +89,17 @@ describe Homebrew::MissingFormula do
       end
     end
 
+    include_examples "it detects deleted formulae"
+
+    describe "on the core tap" do
+      before do
+        allow_any_instance_of(Tap).to receive(:core_tap?).and_return(true)
+      end
+
+      include_examples "it detects deleted formulae"
+    end
+  end
+
   describe "::cask_reason", :cask do
     subject { described_class.cask_reason(formula, show_info: show_info) }