[PROF-10112] Simplify method names from actionview templates in profiler

[ivoanjo]

What does this PR do?

Rails's ActionView likes to dynamically generate method names with suffixed hashes/ids, resulting in methods with names such as _app_views_layouts_explore_html_haml__2304485752546535910_211320.

This makes these stacks not aggregate well, as well as being not-very-useful data.

This PR modifies the stack collector to detect such methods and simplify them by slicing the hash/id suffix.

Motivation:

Improve quality of aggregated flamegraph.

Additional Notes:

N/A

How to test the change?

Change includes test coverage. Also, all of our internal Rails test apps use templates, so by searching by methods with erb or haml we'll be able to validate they no longer end with the ids.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.91%. Comparing base (849c60c) to head (5c6441a).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3759      +/-   ##
==========================================
- Coverage   97.91%   97.91%   -0.01%     
==========================================
  Files        1241     1241              
  Lines       74632    74654      +22     
  Branches     3605     3605              
==========================================
+ Hits        73074    73095      +21     
- Misses       1558     1559       +1     

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[p-datadog]

Do you expect any string without _app_ prefix to be altered by this logic? If this is specifically for Rails maybe check for this prefix?

[ivoanjo]

Do you expect any string without app prefix to be altered by this logic? If this is specifically for Rails maybe check for this prefix?

This is a good point! I double-checked and the answer is actually that the prefix is the path to the template, .e.g _app_views_layouts_explore_html_haml__2304485752546535910_211320 is app/views/layouts/explore.html.haml.

And because it's a path, it's actually possible to change it. By using Rails.application.config.paths['app/views'].unshift(Rails.root.join('testcustom', 'views')) and then moving the file I got a frame named _testcustom_views_pages_about_html_erb for a test app I spun up.

So while I don't think it'll be very common that the template will come from outside the app folder, it can in rare situations, so I'm leaning towards keeping the more generic version.

I also don't think it would particularly be faster -- since we already have the file name filter (not ".rb") + most methods don't end with numbers, this should be enough to filter out almost all methods which are not templates.

[ivoanjo]

I've gone ahead and merged the PR, but LMK if you think I should give another look at focusing only on the _app_ prefix 🙏 🙇

[p-datadog]

My concern was that if someone has their methods named with numeric suffixes that happen to match Rails' generated method names that this PR is considering, they would have their methods unexpectedly renamed. But I wouldn't expect such naming to be very common either.

[ivoanjo]

My concern was that if someone has their methods named with numeric suffixes that happen to match Rails' generated method names that this PR is considering, they would have their methods unexpectedly renamed. But I wouldn't expect such naming to be very common either.

Yeah, they'd need to be quite unlucky:

• Ends with __ + number + _ + number
• Filename is not .rb

Hopefully the current version is good enough; if someone ever triggers this by accident we'll have examples on how to tighten the pattern to not match the accidental one as well :)