[Buildroot] [PATCH RFC 1/2] package/meson: look for qt6 tools on Buildroot host machine

[Quentin Schulz]

From: Quentin Schulz <quentin.schulz at cherry.de>

Qt tools that are looked by the meson qt module are only required as a
build time dependency, to be run on the Buildroot host machine.

Therefore, meson should be looking for them on the host machine and not
on the Buildroot target.

This fixes Buildroot meson not being able to find the qt6 tools whenever
necessary (e.g. for libcamera qcam, whose support is added in a later
commit).

Signed-off-by: Quentin Schulz <quentin.schulz at cherry.de>
---
 ...e-look-for-qt-tools-only-on-build-machine.patch | 56 ++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/package/meson/0001-qt-module-look-for-qt-tools-only-on-build-machine.patch b/package/meson/0001-qt-module-look-for-qt-tools-only-on-build-machine.patch
new file mode 100644
index 0000000000000000000000000000000000000000..c00ae0dbc3c63296afdc8a3d245091ee8337ddd8
--- /dev/null
+++ b/package/meson/0001-qt-module-look-for-qt-tools-only-on-build-machine.patch
@@ -0,0 +1,56 @@
+From b42daeeb3396df1a02c95d2f583058a74e7854e3 Mon Sep 17 00:00:00 2001
+From: Quentin Schulz <quentin.schulz at cherry.de>
+Date: Tue, 18 Mar 2025 15:07:53 +0100
+Subject: [PATCH] qt module: look for qt tools only on build machine
+
+Qt tools may be needed at build time, let's make their detection based
+on the build machine rather than the host machine as currently done.
+
+This incidentally fixes cross-compilation search for moc, rcc, uic and
+lrelease Qt tools because they are installed in libexec dir and that
+path is somehow not properly looked for otherwise.
+
+Before:
+
+"""
+Detecting Qt6 tools
+Run-time dependency qt6 (modules: Core) found: YES 6.8.1 (pkg-config)
+Program /usr/bin/moc found: NO
+Program /usr/lib/qt6/libexec/moc found: NO
+Program moc6 found: NO
+Program moc-qt6 found: NO
+Program moc found: NO
+"""
+
+After:
+
+"""
+Detecting Qt6 tools
+Found pkg-config: YES (/home/qschulz/work/upstream/buildroot/output/host/bin/pkg-config) 2.3.0
+Build-time dependency qt6 (modules: Core) found: YES 6.8.1 (pkg-config)
+Program /home/qschulz/work/upstream/buildroot/output/host/bin/moc found: NO
+Program /home/qschulz/work/upstream/buildroot/output/host/libexec/moc found: YES 6.8.1 6.8.1 (/home/qschulz/work/upstream/buildroot/output/host/libexec/moc)
+"""
+
+Suggested-by: Ross Burton <ross.burton at arm.com>
+Signed-off-by: Quentin Schulz <quentin.schulz at cherry.de>
+Upstream: Submitted [https://github.com/mesonbuild/meson/pull/14381]
+Signed-off-by: Quentin Schulz <quentin.schulz at cherry.de>
+---
+ mesonbuild/modules/_qt.py | 3 +++
+ 1 file changed, 3 insertions(+)
+
+diff --git a/mesonbuild/modules/_qt.py b/mesonbuild/modules/_qt.py
+index 7d52842f9..309068c51 100644
+--- a/mesonbuild/modules/_qt.py
++++ b/mesonbuild/modules/_qt.py
+@@ -270,6 +270,9 @@ class QtBaseModule(ExtensionModule):
+         self._tools_detected = True
+         mlog.log(f'Detecting Qt{self.qt_version} tools')
+         kwargs = {'required': required, 'modules': 'Core', 'method': method}
++        # Tools are for compile-time steps, so force native check for
++        # compatibility with cross-compile scenarios
++        kwargs["native"] = True
+         # Just pick one to make mypy happy
+         qt = T.cast('QtPkgConfigDependency', find_external_dependency(f'qt{self.qt_version}', state.environment, kwargs))
+         if qt.found():

-- 
2.49.0