jest-diff: Add includeChangeCounts and rename Indicator options

[pedrottimark]

Summary

Knowing the number of change lines can help interpret a diff, for example:

• only delete lines
• only insert lines
• equal number of delete and insert lines
• almost equal number of delete and insert lines
• quite unequal number of delete and insert lines

Question for separate pull request: include change counts in report when Jest matcher fails?

Test plan

Updated 18 and added 6 tests to diff.test.ts

See also pictures in the following comment

[pedrottimark]

#8982 moved the indicators to precede the counts instead of follow them:

- Expected  - 0
+ Received  + 3

EDITED: improvement is at right of annotation lines

Example of insert in default export with ordinary matcher colors:

Example of change in diffStringsUnified with current snapshot colors:

Example of insert and change in default export with possible future snapshot colors:

[codecov-io]

Codecov Report

Merging #8881 into master will increase coverage by 0.1%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #8881     +/-   ##
=========================================
+ Coverage   64.11%   64.21%   +0.1%     
=========================================
  Files         275      275             
  Lines       11623    11657     +34     
  Branches     2846     2847      +1     
=========================================
+ Hits         7452     7486     +34     
  Misses       3545     3545             
  Partials      626      626

Impacted Files	Coverage Δ
packages/jest-diff/src/normalizeDiffOptions.ts	100% <ø> (ø)	⬆️
packages/jest-diff/src/diffLines.ts	97.12% <100%> (+0.19%)	⬆️
packages/jest-diff/src/printDiffs.ts	96.47% <100%> (+1.47%)	⬆️

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[jeysal]

Cool feature!

[jeysal]

Have you considered the format

-1  Expected
+2  Received

? It is perhaps less likely to be mistaken for the total line counts of Expected/Received if the number is close together with the +/-.
Maybe there's prior art in other diff renderers?

[pedrottimark]

You have a gift for identifying realistic first impressions!

Let’s explore alternatives. An earlier prototype was to repeat the + and - something like:

- Expected  -1
+ Received  +2

but the option for alternative symbols like < or > made me think twice.

[pedrottimark]

What is your interpretation if you see a ratio?

- Expected  1 / 2
+ Received  2 / 3

[jeysal]

What is your interpretation if you see a ratio?

Not very clear to me, esp. since the sign is still far from the number.

Brainstorming things to show both number (not final):

5 Expected (-1)
6 Received (+2)

But I'm not sure if showing the totals is a good idea at all, if you just look at 5,6 it looks like just one line differs when it really could be 11.

[pedrottimark]

Yes, I agree that totals were unclear. Here a line from git diff --stat

1 file changed, 91 insertions(+), 22 deletions(-)

It suggested symbols following counts. For example, with two sets of options:

Let’s keep the labels aligned with the first column of compared content

[pedrottimark]

Maybe there's prior art in other diff renderers?

That question lead me to discover that git diff uses the term indicator:

--output-indicator-new=<char>
--output-indicator-old=<char>
--output-indicator-context=<char>
Specify the character used to indicate new, old or context lines in the generated patch.
Normally they are +, - and ' ' respectively.

Is it helpful (and not too late) to change the options from aSymbol to aIndicator and so on?

[SimenB]

Is it helpful (and not too late) to change the options from aSymbol to aIndicator and so on?

Should be good to change - 25 isn't stable yet

[github-actions]

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