fix(HF-268): support consecutive percent operators

[Tobiadefami]

Formulas such as =5%% failed to parse even though =(5%)% worked. Consume consecutive postfix percent operators and wrap the preceding expression for each token, so =5%% returns 0.0005 and =5%%% returns 0.000005, matching Excel.

Preserve each operator's whitespace and the existing operator precedence. Document the behavior in the operator guide and Unreleased changelog.

Validated with the matching fix/HF-268 test branch: 502 Jest suites and 6,254 tests passed, and Chrome and Firefox each passed 6,254 tests. Compilation and performance benchmarks passed. Full lint passed with zero errors and existing warnings using the test TypeScript project.

Context

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Types of changes

• Breaking change (a fix or a feature because of which an existing functionality doesn't work as expected anymore)
• New feature or improvement (a non-breaking change that adds functionality)
• Bug fix (a non-breaking change that fixes an issue)
• Additional language file, or a change to an existing language file (translations)
• Change to the documentation

Related issues:

1. Fixes #...

Checklist:

• I have reviewed the guidelines about Contributing to HyperFormula and I confirm that my code follows the code style of this project.
• I have signed the Contributor License Agreement.
• My change is compliant with the OpenDocument standard.
• My change is compatible with Microsoft Excel.
• My change is compatible with Google Sheets.
• I described my changes in the CHANGELOG.md file.
• My changes require a documentation update.
• My changes require a migration guide.

---

Note

Low Risk
Localized parser grammar change for postfix % with existing AST builder; behavior aligns with Excel for previously failing formulas.

Overview
Fixes formula parsing so multiple postfix % operators chain on the same atomic expression, matching Excel (e.g. =5%% → 0.0005 instead of failing while =(5%)% worked).

The parser rule rightUnaryOpAtomicExpression now consumes zero or more % tokens and applies buildPercentOpAst repeatedly on the growing expression, preserving operator whitespace and precedence. Docs clarify that each % divides by 100, and the Unreleased changelog records the fix.

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[cla-external-contractor-signup]

@Tobiadefami thanks for the pull request. No CLA step needed here — our records show you signed the Contributor License Agreement on 2026-07-31. That signature came from our previous signing form and has been carried over, so there is nothing for you to re-sign.

[qunabu]

Task linked: HF-268 Promile operator (%%)

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.32%. Comparing base (c920375) to head (56a15f1).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1773      +/-   ##
===========================================
- Coverage    97.32%   97.32%   -0.01%     
===========================================
  Files          195      195              
  Lines        15739    15738       -1     
  Branches      3390     3460      +70     
===========================================
- Hits         15318    15317       -1     
+ Misses         421      413       -8     
- Partials         0        8       +8     

Files with missing lines	Coverage Δ
src/parser/FormulaParser.ts	97.37% <100.00%> (-0.01%)	⬇️

... and 5 files with indirect coverage changes

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[github-actions]

Performance comparison of head (5361c44) vs base (c920375)

                                     testName |    base |    head | change
--------------------------------------------------------------------------
                                      Sheet A |   508.5 |  506.77 | -0.34%
                                      Sheet B |  163.62 |  164.46 | +0.51%
                                      Sheet T |  144.86 |  144.85 | -0.01%
                                Column ranges |  481.33 |  486.04 | +0.98%
                                Sorted lookup | 14752.7 | 14501.3 | -1.70%
Sheet A:  change value, add/remove row/column |   16.59 |   16.52 | -0.42%
 Sheet B: change value, add/remove row/column |  149.13 |   143.2 | -3.98%
                   Column ranges - add column |  158.88 |  157.34 | -0.97%
                Column ranges - without batch |  485.82 |  487.93 | +0.43%
                        Column ranges - batch |   121.4 |  119.42 | -1.63%

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	hyperformula-docs	56a15f1	Commit Preview URL Branch Preview URL	Sep 14 2026, 05:25 PM