System.Globalization.Native: configure checks ignore CMAKE_ICU_DIR's headers on Unix targets other than wasm #135571

Description

When CMAKE_ICU_DIR is passed for a Unix target other than Android, Apple, Browser and WASI, the two configure checks in System.Globalization.Native/configure.cmake compile without ${CMAKE_ICU_DIR}/include. Without system ICU headers both fail, config.h gets 0 for both, and the build still succeeds. With system ICU headers installed, the checks read those instead.

The bug is latent upstream. Only eng/native.wasm.targets passes CMAKE_ICU_DIR, for wasm, and wasm takes the hard-coded branch at the top of configure.cmake. Other Unix targets hit the bug only with -cmakeargs -DCMAKE_ICU_DIR=<dir> passed by hand.

With CMAKE_ICU_DIR defined, CMakeLists.txt skips find_path(UCURR_H ...), so UCURR_H is empty here:

configure.cmake:14-15

    if (CLR_CMAKE_TARGET_UNIX)
        set(CMAKE_REQUIRED_INCLUDES ${UCURR_H} ${ICU_HOMEBREW_INC_PATH})

${CMAKE_ICU_DIR}/include is added only after include(configure.cmake) (CMakeLists.txt:59):

CMakeLists.txt:86-87

if (NOT CLR_CMAKE_TARGET_APPLE_MOBILE AND DEFINED CMAKE_ICU_DIR)
    include_directories(${CMAKE_ICU_DIR}/include)

Reproduction Steps

On linux-x64 with no ICU development headers installed, from the root of a clone at d148189:

(mkdir -p artifacts/icu && cd artifacts/icu \
  && curl -sSLO https://github.com/unicode-org/icu/releases/download/release-78.3/icu4c-78.3-sources.tgz \
  && tar xzf icu4c-78.3-sources.tgz && cd icu/source \
  && ./configure --prefix="$PWD/../../static" --enable-static --disable-shared --disable-tests --disable-samples \
  && make -j"$(nproc)" && make install) > icu-build.log
./build.sh libs.native -c Release -cmakeargs "-DCMAKE_ICU_DIR=$PWD/artifacts/icu/static" > native-build.log; echo "build exit code: $?"
grep HAVE_ artifacts/obj/native/net11.0-linux-Release-x64/System.Globalization.Native/config.h

Expected behavior

ICU 78.3 has both UDAT_STANDALONE_SHORTER_WEEKDAYS and ucol_clone:

build exit code: 0
#define HAVE_UDAT_STANDALONE_SHORTER_WEEKDAYS 1
#define HAVE_UCOL_CLONE 1

Actual behavior

build exit code: 0
#define HAVE_UDAT_STANDALONE_SHORTER_WEEKDAYS 0
#define HAVE_UCOL_CLONE 0

artifacts/obj/native/net11.0-linux-Release-x64/CMakeFiles/CMakeConfigureLog.yaml (paths shortened):

src.c:2:22: fatal error: 'unicode/udat.h' file not found
CheckSymbolExists.c:2:10: fatal error: 'unicode/ucol.h' file not found

With HAVE_UDAT_STANDALONE_SHORTER_WEEKDAYS 0, super-short day names use the narrow ones:

pal_calendarData.c:517-521

#if HAVE_UDAT_STANDALONE_SHORTER_WEEKDAYS
            return EnumSymbols(locale, calendarId, UDAT_STANDALONE_SHORTER_WEEKDAYS, 1, callback, context);
#else
            return EnumSymbols(locale, calendarId, UDAT_STANDALONE_NARROW_WEEKDAYS, 1, callback, context);
#endif

HAVE_UCOL_CLONE is read only under STATIC_ICU, which the LOCAL_BUILD configuration of src/native/libs/build-local.sh defines:

pal_collation.c:337-341

#if HAVE_UCOL_CLONE
        pClonedCollator = ucol_clone(pCollator, pErr);
#else
        pClonedCollator = ucol_safeClone(pCollator, NULL, NULL, pErr);
#endif // HAVE_UCOL_CLONE

Configured that way with CMAKE_ICU_DIR added by hand, both values are 0 again, and with -DCMAKE_C_FLAGS=-Werror the build fails:

CC=clang cmake -S src/native/libs/System.Globalization.Native -B <build-dir> -DLOCAL_BUILD:STRING=1 -DCLR_CMAKE_TARGET_UNIX:STRING=1 -DCMAKE_ICU_DIR=<icu-prefix> -DCMAKE_C_FLAGS=-Werror
make -C <build-dir>

pal_collation.c:340:27: error: 'ucol_safeClone_78' is deprecated [-Werror,-Wdeprecated-declarations]

Regression?

No: CMAKE_ICU_DIR first appears in CMakeLists.txt in 0fc8978 (#82393), and configure.cmake has never named it.

Known Workarounds

System ICU headers: the checks then describe that ICU, not the static one.

Configuration

Ubuntu 24.04.4 LTS, x64, clang 18.1.3, CMake 3.28.3, static ICU 78.3, without and with libicu-dev 74.2; ./build.sh libs.native -c Release. Not tried on other OSes.

Other information

Proposed fix: append ${CMAKE_ICU_DIR}/include to CMAKE_REQUIRED_INCLUDES in configure.cmake when CMAKE_ICU_DIR is defined. With it the reproduction prints both values as 1, the -Werror LOCAL_BUILD builds without warnings, and a normal build produces a byte-identical libSystem.Globalization.Native.so.

Options not taken:

• Treat CMAKE_ICU_DIR as wasm-only: nothing in the repo says so, and CMakeLists.txt:86-88 applies it to every target but Apple mobile.
• Move include_directories(${CMAKE_ICU_DIR}/include) above include(configure.cmake): CMake ignores the INCLUDE_DIRECTORIES directory property in these checks; only CMAKE_REQUIRED_INCLUDES counts.
• Set UCURR_H to ${CMAKE_ICU_DIR}/include in CMakeLists.txt: would also work, but gives the find_path result a second meaning, away from the checks.

I have a fix ready and will open a PR for it shortly. Could this be assigned to me?