Fix bundle size diff message

[Gudahtt]

The bundle size diff message is using the wrong point of comparision, leading to misleading results on feature branches that have been merged with develop since they were created.

When this feature was introduced, we went back and forth a few times on what we should be comparing the branch with to get an accurate bundle size comparison.

The first attempt used develop as the point of comparison, but that didn't work because it was a moving target, and because it didn't reflect the changes made on this branch. As bundle increases or decreases were added on develop, they would alter the diff on each feature PR.

Then we chose to use the fork-point of the branch, the commit of develop that the branch forked off of. This works for feature branches that don't merge in develop. But the minute develop gets merged in, then unrelated changes on develop affect the measurement.

The most recent commit from develop on the current branch is a better comparison. Any difference between this commit and the feature branch in terms of bundle size would be attributable to the feature branch changes. This is what merge-base gives us.

Manual Testing Steps

The diff message should show zero changes.

It's hard to test the branch cases directly because this always uses develop as the point of comparison, so we'll have to just watch future PRs to ensure the results make sense.

Pre-merge author checklist

• I've clearly explained:
  • What problem this PR is solving
  • How this problem was solved
  • How reviewers can test my changes
• Sufficient automated test coverage has been added

Pre-merge reviewer checklist

• Manual testing (e.g. pull and build branch, run in browser, test code being changed)
• PR is linked to the appropriate GitHub issue
• IF this PR fixes a bug in the release milestone, add this PR to the release milestone

If further QA is required (e.g. new feature, complex testing steps, large refactor), add the Extension QA Board label.

In this case, a QA Engineer approval will be be required.

[metamaskbot]

Builds ready [cdd47cd]

• builds: chrome, firefox
• builds (beta): chrome, firefox
• builds (flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4
  • common: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
  • content-script: 0
  • contentscript: contentscript
  • disable-console: disable-console
  • inpage: inpage
  • policy-load: policy-load
  • sentry-install: sentry-install
  • ui: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (2242 ± 130 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	97	156	122	18	8
		domContentLoaded	1769	2773	2224	281	135
		load	1839	2794	2242	271	130
		domInteractive	1769	2772	2224	281	135

Bundle size diffs

• background: 0 bytes
• ui: 0 bytes
• common: 0 bytes

[Gudahtt]

The solution on develop came from this StackOverflow post: https://stackoverflow.com/questions/12516169/git-find-the-oldest-commit-of-mine-which-does-not-exist-in-theirs/12517430#12517430

It's the correct solution to the wrong problem. The diagram demonstrates the change being made here:

[other-branch]     H--I--J   
                  /       \
[develop]        A--B--C--M1--D--E--M2--F--G
                    \      \             \
[current-branch]     H---I--M3---J---K---M4--M--HEAD

Previously we'd be getting B, the fork point for the current branch. But when comparing B to HEAD, we're also counting the develop commits B, C, etc, through to F as being caused by the current branch, which isn't accurate.

After this PR, we'll be comparing F to HEAD.

At first I thought this would be skipping the effects of commits H and I, J, etc. but that's not really the case. They still are a part of the changeset in HEAD, they're there and accounted for. By comparing F, we can be confident that everything between there and HEAD is a result of this branch.

[metamaskbot]

Builds ready [eb81646]

• builds: chrome, firefox
• builds (beta): chrome, firefox
• builds (flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4
  • common: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
  • content-script: 0
  • contentscript: contentscript
  • disable-console: disable-console
  • inpage: inpage
  • policy-load: policy-load
  • sentry-install: sentry-install
  • ui: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (2173 ± 98 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	92	380	123	60	29
		domContentLoaded	1740	2485	2154	202	97
		load	1740	2485	2173	203	98
		domInteractive	1740	2485	2154	202	97

Bundle size diffs

• background: 0 bytes
• ui: 0 bytes
• common: 0 bytes

[digiwand]

Nice 🙌