Fix C1021 fatal error when building DataSQLite with POCO_SQLITE_UNBUNDLED on MSVC

[uilianries]

Hello Poco maintainers! 👋

Summary

When building Poco 1.15.2 on Conan via PR conan-io/conan-center-index#29722, a new compilation error came when building on Windows with MSVC and POCO_UNBUNDLED=ON:

[603/669] Building CXX object Data\SQLite\CMakeFiles\DataSQLite.dir\src\Utility.cpp.obj
FAILED: Data/SQLite/CMakeFiles/DataSQLite.dir/src/Utility.cpp.obj 
C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\cl.exe  /nologo /TP -DPOCO_CMAKE -DPOCO_DLL -DPOCO_ENABLE_FASTLOGGER -DPOCO_NO_AUTOMATIC_LIBS=1 -DPOCO_OS_FAMILY_WINDOWS -DPOCO_SQLITE_UNBUNDLED -DPOCO_UNBUNDLED -DSQLITE_API=__declspec(dllimport) -DSQLITE_THREADSAFE=1 -DSQLParser_EXPORTS -DSQLite_EXPORTS -DUNICODE -DXML_DTD=1 -D_UNICODE -IC:\j\29722-6\b\pocoeaefe95cf9364\b\src\Data\SQLite\include -IC:\j\29722-6\b\pocoeaefe95cf9364\b\src\Data\SQLite\src -IC:\j\29722-6\b\pocoeaefe95cf9364\b\src\Data\include -IC:\j\29722-6\b\pocoeaefe95cf9364\b\src\Data\src -IC:\j\29722-6\b\pocoeaefe95cf9364\b\src\Foundation\include -IC:\j\29722-6\b\pocoeaefe95cf9364\b\src\dependencies\tessil\include -IC:\j\29722-6\b\pocoeaefe95cf9364\b\src\dependencies\quill\include -external:IC:\j\29722-6\sqlita6b10382efd94\p\include -external:W0 /DWIN32 /D_WINDOWS /EHsc /Zc:__cplusplus /O2 /Ob2 /DNDEBUG -std:c++20 -MD /showIncludes /FoData\SQLite\CMakeFiles\DataSQLite.dir\src\Utility.cpp.obj /FdData\SQLite\CMakeFiles\DataSQLite.dir\ /FS -c C:\j\29722-6\b\pocoeaefe95cf9364\b\src\Data\SQLite\src\Utility.cpp
C:\j\29722-6\b\pocoeaefe95cf9364\b\src\Data\SQLite\src\Utility.cpp(43): fatal error C1021: invalid preprocessor command 'warning'

Full build log: https://c3i.jfrog.io/artifactory/cci-build-logs/cci/prod/PR-29722/6/package_build_logs/build_log_poco_1_15_2_0adc2f8480994b99f01861be3ca8abd7_7c1918cef109f6ba5d4f8f80693ced80922aa350.txt

Note that it was not seen for version 1.14.2, which is distributed/built by Conan. It could be related to #4996, as we started to see it after 1.15.z only.

Cause of the Problem

MSVC does not support the #warning preprocessor directive (it is a GCC/Clang extension). When building with -DPOCO_SQLITE_UNBUNDLED on Windows, the compiler emits a fatal error:

fatal error C1021: invalid preprocessor command 'warning'

References:

• https://learn.microsoft.com/en-us/cpp/preprocessor/warning?view=msvc-170
• https://gcc.gnu.org/onlinedocs/gcc-4.4.3/gcc/Diagnostic-Pragmas.html
• https://gcc.gnu.org/onlinedocs/cpp/Diagnostics.html
• https://clang.llvm.org/docs/UsersManual.html#controlling-diagnostics-via-pragmas

Proposed Fix

#pragma message(...) is supported by MSVC, GCC, and Clang, making it a portable drop-in replacement. The message text is preserved, prefixed with WARNING: to retain its intent.

I applied the proposed patch on Conan side, so we can validate it on the CI as well:

• The same patch overs 1.15.2: conan-io/conan-center-index@871e920
• Build log on Windows with that patch applied: https://c3i.jfrog.io/artifactory/cci-build-logs/cci/prod/PR-29722/7/package_build_logs/build_log_poco_1_15_2_10e5cff93d1fde2e8d6a95ff0bf19527_7c1918cef109f6ba5d4f8f80693ced80922aa350.success.txt

Affected configuration

• Platform: Windows
• Poco version: 1.15.2 (probably 1.15.0 and 1.15.1 as well)
• Compiler: Visual Studio 17 2022 - MSVC 19.44.35213.0
• Build flag: -DPOCO_SQLITE_UNBUNDLED