build: document preprocessing steps in qt package

Author: fanquake

depends/packages/qt.mk

@@ -194,30 +194,52 @@ define $(package)_extract_cmds
   tar --no-same-owner --strip-components=1 -xf $($(package)_source_dir)/$($(package)_qttools_file_name) -C qttools
 endef
 
+# Preprocessing steps work as follows:
+#
+# 1. Apply our patches to the extracted source. See each patch for more info.
+#
+# 2. Point to lrelease in qttools/bin/lrelease; otherwise Qt will look for it in
+# $(host)/native/bin/lrelease and not find it.
+#
+# 3. Create a macOS-Clang-Linux mkspec using our mac-qmake.conf.
+#
+# 4. After making a copy of the mkspec for the linux-arm-gnueabi host, named
+# bitcoin-linux-g++, replace instances of linux-arm-gnueabi with $(host). This
+# way we can generically support hosts like riscv64-linux-gnu, which Qt doesn't
+# ship a mkspec for. See it's usage in config_opts_* above.
+#
+# 5. Put our C, CXX and LD FLAGS into gcc-base.conf. Only used for non-host builds.
+#
+# 6. Do similar for the win32-g++ mkspec.
+#
+# 7. In clang.conf, swap out clang & clang++, for our compiler + flags. See #17466.
+#
+# 8. Adjust a regex in toolchain.prf, to accomodate Guix's usage of
+# CROSS_LIBRARY_PATH. See #15277.
 define $(package)_preprocess_cmds
   patch -p1 -i $($(package)_patch_dir)/freetype_back_compat.patch && \
   patch -p1 -i $($(package)_patch_dir)/fix_powerpc_libpng.patch && \
-  sed -i.old "s|updateqm.commands = \$$$$\$$$$LRELEASE|updateqm.commands = $($(package)_extract_dir)/qttools/bin/lrelease|" qttranslations/translations/translations.pro && \
   patch -p1 -i $($(package)_patch_dir)/drop_lrelease_dependency.patch && \
-  patch -p1 -i $($(package)_patch_dir)/dont_hardcode_pwd.patch &&\
+  patch -p1 -i $($(package)_patch_dir)/dont_hardcode_pwd.patch && \
+  patch -p1 -i $($(package)_patch_dir)/fix_qt_pkgconfig.patch && \
+  patch -p1 -i $($(package)_patch_dir)/fix_configure_mac.patch && \
+  patch -p1 -i $($(package)_patch_dir)/fix_no_printer.patch && \
+  patch -p1 -i $($(package)_patch_dir)/fix_rcc_determinism.patch && \
+  patch -p1 -i $($(package)_patch_dir)/xkb-default.patch && \
+  patch -p1 -i $($(package)_patch_dir)/fix_android_qmake_conf.patch && \
+  patch -p1 -i $($(package)_patch_dir)/fix_android_jni_static.patch && \
+  patch -p1 -i $($(package)_patch_dir)/fix_riscv64_arch.patch && \
+  patch -p1 -i $($(package)_patch_dir)/no-xlib.patch && \
+  patch -p1 -i $($(package)_patch_dir)/fix_mingw_cross_compile.patch && \
+  sed -i.old "s|updateqm.commands = \$$$$\$$$$LRELEASE|updateqm.commands = $($(package)_extract_dir)/qttools/bin/lrelease|" qttranslations/translations/translations.pro && \
   mkdir -p qtbase/mkspecs/macx-clang-linux &&\
   cp -f qtbase/mkspecs/macx-clang/qplatformdefs.h qtbase/mkspecs/macx-clang-linux/ &&\
   cp -f $($(package)_patch_dir)/mac-qmake.conf qtbase/mkspecs/macx-clang-linux/qmake.conf && \
   cp -r qtbase/mkspecs/linux-arm-gnueabi-g++ qtbase/mkspecs/bitcoin-linux-g++ && \
   sed -i.old "s/arm-linux-gnueabi-/$(host)-/g" qtbase/mkspecs/bitcoin-linux-g++/qmake.conf && \
-  patch -p1 -i $($(package)_patch_dir)/fix_qt_pkgconfig.patch &&\
-  patch -p1 -i $($(package)_patch_dir)/fix_configure_mac.patch &&\
-  patch -p1 -i $($(package)_patch_dir)/fix_no_printer.patch &&\
-  patch -p1 -i $($(package)_patch_dir)/fix_rcc_determinism.patch &&\
-  patch -p1 -i $($(package)_patch_dir)/xkb-default.patch &&\
-  patch -p1 -i $($(package)_patch_dir)/fix_android_qmake_conf.patch &&\
-  patch -p1 -i $($(package)_patch_dir)/fix_android_jni_static.patch &&\
   echo "!host_build: QMAKE_CFLAGS     += $($(package)_cflags) $($(package)_cppflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
   echo "!host_build: QMAKE_CXXFLAGS   += $($(package)_cxxflags) $($(package)_cppflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
   echo "!host_build: QMAKE_LFLAGS     += $($(package)_ldflags)" >> qtbase/mkspecs/common/gcc-base.conf && \
-  patch -p1 -i $($(package)_patch_dir)/fix_riscv64_arch.patch &&\
-  patch -p1 -i $($(package)_patch_dir)/no-xlib.patch &&\
-  patch -p1 -i $($(package)_patch_dir)/fix_mingw_cross_compile.patch && \
   sed -i.old "s|QMAKE_CFLAGS           += |!host_build: QMAKE_CFLAGS            = $($(package)_cflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
   sed -i.old "s|QMAKE_CXXFLAGS         += |!host_build: QMAKE_CXXFLAGS            = $($(package)_cxxflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
   sed -i.old "0,/^QMAKE_LFLAGS_/s|^QMAKE_LFLAGS_|!host_build: QMAKE_LFLAGS            = $($(package)_ldflags)\n&|" qtbase/mkspecs/win32-g++/qmake.conf && \