feat(ishikawa): support empty gap branched with []

[sillydan1]

📑 Summary

This PR adds the possibility of specifying an "empty" branch in ishikawa diagrams. This is useful when you have long branch descriptions that would have the text collide with other branches.

Demonstration of the problem:

ishikawa
    Demo
    Category
        Very long branch description that is cool and more text goes here describing the potential cause
        Another long branch name that is less cool, but also describes another potential cause
    Category2
        Very long branch description that is cool and more text goes here describing the potential cause
        Another long branch name that is less cool, but also describes another potential cause

Loading

This PR enables you to add extra spacing between the branches.

ishikawa
    Demo
    Category
        Very long branch description that is cool and more text goes here describing the potential cause
        []
        []
        Another long branch name that is less cool, but also describes another potential cause
    Category2
        Very long branch description that is cool and more text goes here describing the potential cause
        []
        []
        Another long branch name that is less cool, but also describes another potential cause

📏 Design Decisions

I'm unsure about the overall approach here - maybe the real solution is to calculate the bounding boxes of the labels better instead?

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added necessary unit/e2e tests.
• 📓 have added documentation. Make sure MERMAID_RELEASE_VERSION is used for all new features.
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Latest commit: 46b3f83

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commit: 46b3f83

[codecov]

Codecov Report

❌ Patch coverage is 68.18182% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 20.02%. Comparing base (b68b7de) to head (46b3f83).
⚠️ Report is 10 commits behind head on develop.

Files with missing lines	Patch %	Lines
.../mermaid/src/diagrams/ishikawa/ishikawaRenderer.ts	65.00%	3 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #7891       +/-   ##
============================================
- Coverage    77.79%   20.02%   -57.78%     
============================================
  Files          409      184      -225     
  Lines        30328    10134    -20194     
  Branches      5175     1410     -3765     
============================================
- Hits         23595     2029    -21566     
- Misses        5410     8040     +2630     
+ Partials      1323       65     -1258     

Flag	Coverage Δ
e2e	20.02% <68.18%> (-61.95%)	⬇️
unit	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ckages/mermaid/src/diagrams/ishikawa/ishikawaDb.ts	81.25% <100.00%> (+0.60%)	⬆️
.../mermaid/src/diagrams/ishikawa/ishikawaRenderer.ts	89.23% <65.00%> (-2.43%)	⬇️

... and 394 files with indirect coverage changes

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Build	Status	Details	Updated (UTC)
default (Inspect)	✅ No changes detected	-	Jun 19, 2026, 12:33 PM

[sidharthv96]

Thanks for the PR @sillydan1, The problem is clear, but I think we need to change our approach to the problem.

Is there anything stopping us from rendering properly by measuring the size of nodes and adjusting the spacing as required, instead of having to manually add empty spaces?