Only optimize for the core tap

Library/Homebrew/missing_formula.rb

@@ -154,14 +154,17 @@ module Homebrew
             end
           end
 
-          # Check if the formula has been deleted in the last month.
+          # Optimization for the core tap which has many monthly commits
-          diff_command = ["git", "diff", "--diff-filter=D", "--name-only",
+          if tap.core_tap?
-                          "@{'1 month ago'}", "--", relative_path]
+            # Check if the formula has been deleted in the last month.
-          deleted_formula = Utils.popen_read(*diff_command)
+            diff_command = ["git", "diff", "--diff-filter=D", "--name-only",
+                            "@{'1 month ago'}", "--", relative_path]
+            deleted_formula = Utils.popen_read(*diff_command)
 
-          if deleted_formula.blank?
+            if deleted_formula.blank?
-            ofail "No previously deleted formula found." unless silent
+              ofail "No previously deleted formula found." unless silent
-            return
+              return
+            end
           end
 
           # Find commit where formula was deleted in the last month.

Library/Homebrew/test/missing_formula_spec.rb

@@ -75,16 +75,28 @@ describe Homebrew::MissingFormula do
       end
     end
 
-    context "with a deleted formula" do
+    shared_examples "it detects deleted formulae" do
-      let(:formula) { "homebrew/foo/deleted-formula" }
+      context "with a deleted formula" do
+        let(:formula) { "homebrew/foo/deleted-formula" }
 
-      it { is_expected.not_to be_nil }
+        it { is_expected.not_to be_nil }
+      end
+
+      context "with a formula that never existed" do
+        let(:formula) { "homebrew/foo/missing-formula" }
+
+        it { is_expected.to be_nil }
+      end
     end
 
-    context "with a formula that never existed" do
+    include_examples "it detects deleted formulae"
-      let(:formula) { "homebrew/foo/missing-formula" }
 
-      it { is_expected.to be_nil }
+    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