UPSTREAM.md
In charr: String Processing Reimagined for 'ALTREP' Strings

ICU4C 78.3 provenance

The runtime source and data come from the official ICU4C 78.3 release:

Release: https://github.com/unicode-org/icu/releases/tag/release-78.3
Source archive: icu4c-78.3-sources.tgz
Source archive SHA-256: 3a2e7a47604ba702f345878308e6fefeca612ee895cf4a5f222e7955fabfe0c0
Source archive SHA-512: 04a49455e1489030c520a4bfd2664fa2171e7938d08f2acdbbcb1fda976639fd8b1f0704f2eec89ba59a7b6d118ceaab6ec5a096e40d9085a0895d91ce225245

common/, i18n/, and stubdata/ contain every .cpp and .h runtime file from the corresponding official source directories. unicode/ combines the public headers from common/unicode/ and i18n/unicode/. These 965 files were imported from the official archive. Charr carries twelve source adjustments for CRAN compiler diagnostics and platform compatibility, listed under "Source-package adjustments" below.

Package-specific static-build settings are supplied by src/Makevars, src/Makevars.win, and src/uconfig_local.h. The last also defines ICU's UPRV_UNREACHABLE_EXIT and double-conversion's DOUBLE_CONVERSION_UNIMPLEMENTED() and DOUBLE_CONVERSION_UNREACHABLE(), which upstream expand to abort(), as calls to charr's handler in src/shared/icu_fatal.cpp; ICU's sources are unchanged, and tools/charr-lint/fatal-sites.tsv lists every expansion. Bundled symbols are suffixed ..._78_charr. DECNUMDIGITS=4 is a build define rather than a modification to ICU's decNumber.h.

The full little-endian data archive in the official source release is icu/source/data/in/icudt78l.dat. It is 33,107,232 bytes with SHA-256 d5cf2a40dccbe471781ec7af85693bff542ff12f0b670c9630c4e72d60714b8b. tools/trim-icudt.R reduces it to the services reachable through charr's API. The resulting 13,478,992-byte archive has SHA-256 0f40045bffbcc40bf53e05198282af67a5cda820388a1d9b04ed36f1dcf55338; the checked-in data/icudt78l.dat.xz has SHA-256 2682cdd764b5e2b36d81bc9f6292035b2cb340896603e3e8ba3197fbada2c0cb.

The full and trimmed 78.3 archives passed the same ICU service canaries and produced no trimming-specific failure in the wider backend comparison.

The bundled runtime sources come from the official ICU4C 78.3 archive, with twelve small changes for CRAN compiler diagnostics and platform compatibility:

common/locmap.cpp uses an overlap-safe move when shortening the Windows language tags quz and prs. The upstream strcat() call had overlapping source and destination ranges.
common/unistr.cpp marks the static destructor-instantiation helper [[maybe_unused]] instead of suppressing -Wunused-function.
i18n/decNumber.cpp leaves the compiler's -Warray-bounds diagnostics enabled around three upstream decimal routines. decGetInt() returns BADINT when a partial unit's digit count is outside 1 .. DECDPUN-1. ICU defines DECDPUN as 1, so that branch is only reached when negating the exponent overflows; defined exponents still take the whole-unit path.
i18n/formattedvalue.cpp omits the unused ufmtval_getString() definition, as stringi does. GCC reports a false -Wreturn-local-addr diagnostic for the upstream implementation.
i18n/number_skeletons.cpp keeps the temporary UnicodeString alias alive through CurrencyUnit construction instead of suppressing -Wdangling-pointer.
i18n/collationiterator.h and i18n/collationdatabuilder.cpp finish constructing the builder's CollationData before binding it to the base iterator. The upstream constructor read that derived member too early.
i18n/windtfmt.cpp and i18n/winnmfmt.cpp skip the optional ResolveLocaleName() lookup on 32-bit Windows. Rtools40 does not provide the symbol, and ICU already falls back to the Windows user locale when the lookup is unavailable. This follows the fix for stringi issue 501.
common/putil.cpp copies one byte fewer than the code-page buffer in getCodepageFromPOSIXID() and still writes the terminating NUL. The previous strncpy bound was the destination size, which GCC reports as -Wstringop-truncation. A shorter source still zero-fills, and a longer source still keeps the same prefix.
common/udata.cpp declares the linked-in data symbol with stubdata's ICU_Data_Header type. The old DataHeader declaration was a different type for the same object and tripped -Wodr under LTO. Call sites that need a DataHeader * cast the address; the object bytes are unchanged.
common/rbbidata.h, common/rbbi.cpp, common/rbbitblb.cpp, and common/rbbidata.cpp read and write RBBIStateTableRowT::fNextState with pointer arithmetic on its first element. The array is a trailing struct-hack member of declared length 1, allocated to the category count. A subscript makes -fsanitize=bounds report that declared length.
i18n/regeximp.h and i18n/rematch.cpp use the same pointer arithmetic for every REStackFrame::fExtra access, including addresses of elements. The frame is allocated to fFrameSize; the declared length is 1.
unicode/char16ptr.h, unicode/ucol.h, and unicode/unistr.h treat libc++ 17 like libc++ 18: the std::basic_string_view<uint16_t> overloads are compiled only before libc++ 17 (upstream: before 18), and the UnicodeString(const uint16_t *) constructor that replaces them is compiled from libc++ 17. libc++ 17 deprecates std::char_traits for uint16_t, so the upstream gates made every translation unit including these headers report -Wdeprecated-declarations (seen with Apple clang 17 and the macOS 14 SDK). ICU's own libc++ 18 path is unchanged.

The platform-specific optimization and macro-state pragmas remain unchanged; they do not suppress compiler diagnostics.

ICU's deprecation attribute is disabled only while compiling bundled ICU objects. ICU 78.3 still calls deprecated public entry points inside its own implementation, and some replacement APIs call these older routines too. Charr's objects retain the annotations, and other compiler diagnostics remain enabled.