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fix(sequenceDiagram): allow empty message after colon (Fixes #6518) #6523

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Merged
merged 3 commits into from
Apr 28, 2025
Merged

fix(sequenceDiagram): allow empty message after colon (Fixes #6518) #6523

merged 3 commits into from
Apr 28, 2025

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NourBenz
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@NourBenz NourBenz commented Apr 22, 2025 •
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📑 Summary

This pull request fixes an issue where sequence diagram arrows with a trailing colon but no message (e.g., B ->> A:) would fail to parse. The grammar previously required at least one character after the colon, which was unnecessarily restrictive.

Resolves #6518

📏 Design Decisions

The lexer rule for TXT was too strict, requiring one or more characters after the colon. This PR modifies the rule to allow zero or more characters (* instead of +), and adds a fallback pattern to match a standalone colon.

🔧 Lexer Fix

":"(?:(?:no)?wrap:)?[^#\n;]*                                    return 'TXT';
":"                                                             return 'TXT';

This enables syntax such as:

sequenceDiagram
A ->> B:
B ->> A: response

which now parses correctly.

No changes were needed in the parser or rendering logic since TXT is already processed safely as an optional message.

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🦋 Changeset detected

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@github-actions github-actions bot added the Type: Bug / Error Something isn't working or is incorrect label Apr 22, 2025
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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 3.87%. Comparing base (cf8fc2a) to head (b821454).
Report is 4 commits behind head on develop.

Additional details and impacted files

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@@            Coverage Diff             @@
##           develop   #6523      +/-   ##
==========================================
- Coverage     3.87%   3.87%   -0.01%     
==========================================
  Files          412     413       +1     
  Lines        43164   43175      +11     
  Branches       665     665              
==========================================
  Hits          1672    1672              
- Misses       41492   41503      +11
Flag Coverage Δ
unit 3.87% <ø> (-0.01%) ⬇️

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see 1 file with indirect coverage changes

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default (Inspect) ✅ No changes detected - Apr 25, 2025, 6:10 PM

@nour0205
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Thanks for this fix!
The lexer rule update looks correct and the unit test covers the basic expected behavior nicely.

I have a few minor improvement suggestions:

Simplification:

Since the updated regex already allows zero or more characters after :, the fallback rule ":" return 'TXT' might now be unnecessary.

Could we check if removing it would still pass all tests? Might help keep the lexer a bit cleaner.

Extra Test Suggestion:

Maybe add a test for input likeAlice ->> Bob: ;(colon + space + semicolon) or colon followed by a comment line, to ensure parsing remains stable even with odd user input.

Versioning:

This is marked as a major bump that makes sense if we assume downstream users might depend on the stricter old behavior. (Just confirming if that was fully intended.)

Overall great work this makes sequence diagrams much more user-friendly!

@knsv
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knsv commented Apr 28, 2025

Thanks @NourBenz. Good update! I appreciate that you added the unit test as well.

@knsv knsv added this pull request to the merge queue Apr 28, 2025
Merged via the queue into mermaid-js:develop with commit 9080431 Apr 28, 2025
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Sequence diagram requires colon and whitespace : after an arrow without label
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@NourBenz @nour0205 @knsv