feat: Enforce feature name lengths and character set

[Bronek]

High Level Overview of Change

This PR enforces a maximum length of 63 characters on feature names, as well as not permitting an exactly 32 character long feature name to avoid confusion with those that use a uint256 hex representation, as that is an alternative way to specify a feature. This change further prevents the use of Unicode characters in feature names, because some can be confused with regular ASCII characters despite being valid in identifiers.

Context of Change

Useful for WASM interop; improved security.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

[mvadari]

If it makes more sense, this PR can be merged into ripple/smart-escrow instead of directly into develop

[intelliot]

@Bronek is there a reason this is still in draft? Just wondering

[intelliot]

notes: this limits feature (amendment) names to <= 63 and prevents names that are exactly 32-33 characters long, because those names would be ambiguous - is it feature name or uint256 hash?

WASM code will use 32-byte strings to select features without ambiguity.

disallowing 33 bytes prevents potential off-by-one mistake since a 32 character string is 33 bytes total (with 1 null terminator byte)

[ximinez]

I'm marking this as "Ready to merge" on @Bronek's behalf. It's got two trusted reviews, and doesn't seem to have bit-rotted.

[Copilot]

Pull request overview

This PR adds compile-time enforcement of feature/amendment name length limits to prevent ambiguous selection (e.g., names colliding with alternate uint256-based selection), and updates the RPC feature unit test to compute/verify the feature ID hash.

Changes:

• Add maxFeatureNameSize and reservedFeatureNameSize constants and enforce them during feature registration via compile-time static_asserts.
• Update XRPL_FEATURE / XRPL_FIX macro expansions to run name literals through the new size-enforcement helper.
• Adjust Feature_test to compute the expected feature ID via sha512Half while still asserting against the fixed known hash.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
include/xrpl/protocol/Feature.h	Introduces public constants for feature name size limits (and documents reserved lengths).
src/libxrpl/protocol/Feature.cpp	Adds compile-time validation helper and wires it into feature/fix registration macros.
src/test/rpc/Feature_test.cpp	Computes expected feature hash dynamically and verifies it matches the known constant.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.8%. Comparing base (7a3bf16) to head (0d38c57).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #5555     +/-   ##
=========================================
- Coverage     79.8%   79.8%   -0.0%     
=========================================
  Files          878     878             
  Lines        67887   67887             
  Branches      7548    7550      +2     
=========================================
- Hits         54207   54205      -2     
- Misses       13680   13682      +2     

Files with missing lines	Coverage Δ
include/xrpl/protocol/Feature.h	97.8% <ø> (ø)
src/libxrpl/protocol/Feature.cpp	94.4% <ø> (ø)

... and 1 file with indirect coverage changes

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[Bronek]

@bthomee @ximinez I added a check to fail compilation if a feature name contains an Unicode character - otherwise we may end up with features which are difficult to work with, but may also look (in many but not all tools) like regular text.

[bthomee]

Looking good and very comprehensive. I would just like to see some additional comments in places that would not be intuitive for the standard developer.