Fix UB and locale-dependent behavior in StringHelper::toLowerCase

[metsw24-max]

Fix undefined behavior and locale-dependent output in StringHelper::toLowerCase.

The previous implementation passed LogString characters directly to ::tolower(int) via std::transform. This violates the C standard requirement that the argument must either be EOF or representable as unsigned char.

When logchar = char (commonly signed), any byte greater than 0x7F sign-extends to a negative int, triggering undefined behavior. The behavior also depended on the active LC_CTYPE locale, causing the same configuration file to produce different lowercased values on different systems.

This patch replaces the locale-sensitive transformation with deterministic ASCII-only folding (A-Z -> a-z) while preserving all non-ASCII bytes unchanged.

Changes

src/main/cpp/stringhelper.cpp

• Replaced:

  • std::transform(..., tolower)

• With:

  • deterministic ASCII-only lowercase conversion

• Eliminates UB from invalid tolower inputs

• Removes locale-dependent behavior

• Preserves non-ASCII bytes unchanged

src/test/cpp/helpers/stringhelpertestcase.cpp

Added regression coverage:

• testToLowerCaseAscii

  • verifies normal ASCII lowercase conversion

• testToLowerCaseNonAsciiPassesThrough

  • verifies non-ASCII bytes remain unchanged
  • validates locale-independent behavior

Reproducer

With the original implementation:

• testToLowerCaseNonAsciiPassesThrough fails on systems using locales such as English_India.1252

• Example:

  • 0xC9 (É) may be transformed into 0xE9 (é) through locale-sensitive tolower

With this patch:

• all stringhelpertestcase tests pass
• patternparsertestcase also passes unchanged