dev-cmd/prof: add vernier support.

It's the newest great profiler for Ruby.

.gitignore

@@ -138,6 +138,7 @@
 **/vendor/bundle/ruby/*/gems/unicode-display_width-*/
 **/vendor/bundle/ruby/*/gems/unparser-*/
 **/vendor/bundle/ruby/*/gems/uri_template-*/
+**/vendor/bundle/ruby/*/gems/vernier-*/
 **/vendor/bundle/ruby/*/gems/webrobots-*/
 **/vendor/bundle/ruby/*/gems/yard-*/
 **/vendor/bundle/ruby/*/gems/yard-sorbet-*/

Library/Homebrew/Gemfile

@@ -41,6 +41,7 @@ end
 group :prof, optional: true do
   gem "ruby-prof", require: false
   gem "stackprof", require: false
+  gem "vernier", require: false
 end
 group :pry, optional: true do
   gem "pry", require: false

Library/Homebrew/Gemfile.lock

@@ -153,6 +153,7 @@ GEM
       unf_ext
     unf_ext (0.0.9.1)
     unicode-display_width (2.5.0)
+    vernier (1.0.1)
     warning (1.3.0)
     yard (0.9.36)
     yard-sorbet (0.8.1)
@@ -201,6 +202,7 @@ DEPENDENCIES
   spoom
   stackprof
   tapioca
+  vernier
   warning
   yard
   yard-sorbet

Library/Homebrew/dev-cmd/prof.rb

@@ -12,6 +12,8 @@ class Prof < AbstractCommand
         EOS
         switch "--stackprof",
                description: "Use `stackprof` instead of `ruby-prof` (the default)."
+        switch "--vernier",
+               description: "Use `vernier` instead of `ruby-prof` (the default)."
 
         named_args :command, min: 1
       end
@@ -39,17 +41,26 @@ def run
         Homebrew.setup_gem_environment!
 
         if args.stackprof?
+          # odeprecated. vernier is better in every way
           with_env HOMEBREW_STACKPROF: "1" do
             system(*HOMEBREW_RUBY_EXEC_ARGS, brew_rb, *args.named)
           end
           output_filename = "prof/d3-flamegraph.html"
           safe_system "stackprof --d3-flamegraph prof/stackprof.dump > #{output_filename}"
+          exec_browser output_filename
+        elsif args.vernier?
+          output_filename = "prof/vernier.json"
+          Process::UID.change_privilege(Process.euid) if Process.euid != Process.uid
+          safe_system "vernier", "run", "--output=#{output_filename}", "--allocation_sample_rate=500", "--",
+                      RUBY_PATH, brew_rb, *args.named
+          ohai "Profiling complete!"
+          puts "Upload the results from #{output_filename} to:"
+          puts "  #{Formatter.url("https://vernier.prof")}"
         else
           output_filename = "prof/call_stack.html"
           safe_system "ruby-prof", "--printer=call_stack", "--file=#{output_filename}", brew_rb, "--", *args.named
+          exec_browser output_filename
         end
-
-        exec_browser output_filename
       rescue OptionParser::InvalidOption => e
         ofail e