[all-commits] [llvm/llvm-project] cb180d: [cmake] FindLibXml2: keep user-provided LIBXML2_DE...

[Ryan VanderMeulen via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cb180d50a81674b467887eab836f563607ae89e8
      https://github.com/llvm/llvm-project/commit/cb180d50a81674b467887eab836f563607ae89e8
  Author: Ryan VanderMeulen <ryanvm at gmail.com>
  Date:   2026-09-08 (Tue, 08 Sep 2026)

  Changed paths:
    M llvm/cmake/modules/FindLibXml2.cmake

  Log Message:
  -----------
  [cmake] FindLibXml2: keep user-provided LIBXML2_DEFINITIONS (#221294)

LLVM's `FindLibXml2.cmake` (added in #166867) unconditionally does
`set(LIBXML2_DEFINITIONS ${PC_LIBXML_CFLAGS_OTHER})` and puts
`PC_LIBXML_CFLAGS_OTHER` on the imported targets. CMake's own
`FindLibXml2` module only takes pkg-config's flags when the library it
found is the one pkg-config describes; otherwise it keeps whatever
`LIBXML2_DEFINITIONS` the user passed and exposes it through
`INTERFACE_COMPILE_OPTIONS`.

This matters when cross-compiling against a static libxml2 on Windows.
Passing `-DLIBXML2_DEFINITIONS=-DLIBXML_STATIC
-DLIBXML2_LIBRARIES=.../libxml2s.lib` worked with LLVM 22 (CMake's
module): the define reached both the `xmlReadMemory` configure check and
the consumers of `LibXml2::LibXml2`. With LLVM 23 it is silently
dropped, `xmlexports.h` declares the API `__declspec(dllimport)`, the
check fails to link against the static library and
`LLVM_ENABLE_LIBXML2=FORCE_ON` aborts with `Failed to configure
libxml2`. (pkg-config on the Linux host finds the host's libxml2, so
`PC_LIBXML_CFLAGS_OTHER` is empty and unrelated to the library actually
being used.)

Mirror CMake's behaviour: keep the user's definitions unless pkg-config
found the same library, and attach them to both `LibXml2::LibXml2` and
`LibXml2::LibXml2Static`.

Seen while building the Firefox clang 23 toolchains (x86_64 and aarch64
`-pc-windows-msvc`, cross-compiled from Linux with
`LLVM_EXPORT_SYMBOLS_FOR_PLUGINS=ON`).

---
**AI tool use disclosure** (per the [LLVM AI Tool Use
Policy](https://llvm.org/docs/AIToolPolicy.html)): this change was
developed with Claude Code assisting in the analysis and drafting. The
root cause was established against real 23.1.0 binaries; this cmake
change itself has so far only been verified to apply to 23.1.0 and main
and by code reading, while Firefox's CI validated the equivalent
workaround of passing -DLIBXML_STATIC via the compiler flags. The author
reviewed the change and is accountable for and able to answer questions
about it. Commits carry an `Assisted-by:` trailer.



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