Version 2.7.0: Audit and documentation

This version adds a FileSize validator, a PositionalOnly prefix command mode, and more control over config file generation. It also contains a large set of bug fixes from a systematic audit of the parsing, config, help formatting, string handling, and type conversion code, along with performance improvements that remove unnecessary copies in hot paths.

Added

• Added a FileSize validator to check minimum and maximum file sizes. #1305
• Added PrefixCommandMode::PositionalOnly, which restores the pre-2.6.2 prefix command behavior as an opt-in mode: only a positional argument or the -- separator triggers prefix mode, and unrecognized options are collected as extras. #1382
• Added an option to write only the active subcommand defaults when generating a config file. #1314

Changed

• Improved performance by removing unnecessary string and container copies in parsing and validator hot paths. #1368
• Improved the performance of string splitting by replacing a stringstream with a find-based loop. #1396
• Sorted the excludes and needs sets by name for stable help output. #1308
• Removed en_US.UTF-8 from the unicode locale fallback list. #1312
• Modernization and portability fixes: added missing standard includes, exported CLI::Number from the C++20 module, and cleaned up the warning lists. #1367
• Aligned the Meson build with wrapdb policy by removing disable_auto_if for subprojects. #1349

Fixed

• Fixed require_subcommand maximum enforcement for dot notation and for disabled fallthrough, dot-notation subcommands with Windows-style prefixes, get_options const/non-const consistency, and a crash when parsing with argc == 0. #1363, #1384
• Fixed missing symbol export from the precompiled shared library on macOS. #1387
• Fixed double indentation of nested option groups in help output. #1371, #1379
• Fixed config reading and writing bugs: section headers with trailing comments, one-line multiline comments, embedded delimiters with the Join policy, and multiline values for indented keys. #1369, #1361
• Fixed help formatting issues: hidden positionals appearing in the usage line, long subcommand names running into their descriptions, and ExtrasError reporting the wrong error name. #1369
• Fixed ignore_case and ignore_underscore so both apply when used together. #1358
• Fixed string handling edge cases in split_up, remove_quotes, append_codepoint, and escape_detect. #1364
• Fixed type conversion edge cases: negative input to unsigned types, whitespace-only floating point input, containers of pairs with an odd element count, large integer sums, and the Join policy with default values. #1362
• Fixed stale processed values being returned after Option::clear(). #1360
• Fixed out-of-bounds reads in the non-codecvt narrow/widen conversion paths used under C++26. #1359
• Fixed infinite recursion on subcommand option groups with fallthrough enabled. #1316
• Fixed empty strings given to wrapper types such as std::optional to consistently produce a default-constructed value. #1340
• Fixed CLI::ExistingFile to reject an empty filename with a clear error. #1351
• Fixed an empty description on a modified Transformer. #1345
• Fixed unsigned wraparound in split_program_name for command lines without spaces. #1339
• Fixed FileOnDefaultPath with an empty default path, and PositiveNumber rejecting subnormal values. #1366
• Fixed compilation with libc++/clang in C++26 mode. #1326
• Fixed the case of the shell32 library name in CMake. #1347
• Removed the static keyword from the precompiled library definition in CMake. #1304

Documentation

• Clarified the behavior of the prefix_command overloads. #1310
• Documented the Catch2 dependency for the test build. #1342
• Corrected documentation errors, including the AsSizeValue example, the App::required() doc, and validator comments. #1304, #1366
• Modernized some documentation. #1336
• Moved the tutorial book into the Doxygen documentation, modernized the HTML output with doxygen-awesome-css, and reorganized the sidebar navigation. #1390, #1392, #1397, #1398
• Corrected errors found in a documentation review. #1394
• Split the documentation into Guide and Examples sections and filled gaps in the guide. #1400

Internal

• Added a dev CMake preset and workflow for faster local iteration using the precompiled library and ccache. #1387
• Added a CUDA test for the single-header build. #1381
• Refactored the duplicated parse-completion pipeline and removed dead code. #1365
• Moved static std::string reference initializers to helper functions. #1335
• Routed formatter label fallback through an internal helper as a step toward internationalization support. #1320
• Cleaned up the CMake logic for finding Catch2 and Boost, and corrected the example test regular expressions. #1325, #1322
• Reorganized the GitHub workflows and reduced CI build times. #1323, #1387
• Added C++26 CI coverage (GCC, and clang with modules), and made codecov wait for all coverage uploads. #1388, #1391
• Tidied the configuration files in the root directory. #1393
• Attached the source packages to tagged releases, wrote the release notes from the changelog, and added a CI check for a changelog entry on every build. #1401, #1402, #1403