Utils.popen_read: Nonexistent program should fail

Ensure that $CHILD_STATUS.success? is false when the command does not exist.

Library/Homebrew/test/utils/popen_spec.rb

@@ -15,6 +15,12 @@ describe Utils do
       ).to eq("success")
       expect($CHILD_STATUS).to be_a_success
     end
+
+    it "fails when the command does not exist" do
+      expect(subject.popen_read("./nonexistent", err: :out))
+        .to eq("brew: command not found: ./nonexistent\n")
+      expect($CHILD_STATUS).to be_a_failure
+    end
   end
 
   describe "::popen_write" do

Library/Homebrew/utils/popen.rb

@@ -14,7 +14,15 @@ module Utils
         yield pipe
       else
         options[:err] ||= :close unless ENV["HOMEBREW_STDERR"]
-        exec(*args, options)
+        begin
+          exec(*args, options)
+        rescue Errno::ENOENT
+          $stderr.puts "brew: command not found: #{args[0]}" unless options[:err] == :close
+          exit! 127
+        rescue SystemCallError
+          $stderr.puts "brew: exec failed: #{args[0]}" unless options[:err] == :close
+          exit! 1
+        end
       end
     end
   end