qmake shadow build problem using QMAKE_EXTRA_COMPILERS

mcarter

QMake version 3.1
Qt version 5.9.7 (also tried in 5.15.2)

I created a simple project that demonstrates the problem I am having with performing a shadow build and using QMAKE_EXTRA_COMPILERS.

This is the layout of my files based from /tmp/test:

├── shadow
│   └── Makefile
└── src
    ├── gen.pro
    ├── main.cpp
    ├── test1.xrt
    ├── test2.xrt
    └── test3.xrt

gen.pro:

TEMPLATE = app
TARGET = gen
INCLUDEPATH += .
SOURCES += main.cpp

target.path = /tmp/data
INSTALLS += target

#
XRT_FILES = test1.xrt test2.xrt test3.xrt
gen_headers.input = XRT_FILES
gen_headers.output = ${QMAKE_FILE_BASE}.h
gen_headers.commands = $(COPY) ${QMAKE_FILE_IN} ${QMAKE_FILE_OUT}
gen_headers.variable_out = MY_HEADERS.files
gen_headers.CONFIG += no_link
QMAKE_EXTRA_COMPILERS += gen_headers

MY_HEADERS.path = $$target.path
MY_HEADERS.CONFIG += no_check_exist
INSTALLS += MY_HEADERS

when I execute "qmake ../src" from the shadow directory the generated Makefile has these install commands for MY_HEADERS:

install_MY_HEADERS: first FORCE
        @test -d $(INSTALL_ROOT)/tmp/data || mkdir -p $(INSTALL_ROOT)/tmp/data
        -$(QINSTALL) /tmp/test/src/test1.h $(INSTALL_ROOT)/tmp/data/test1.h
        -$(QINSTALL) /tmp/test/src/test2.h $(INSTALL_ROOT)/tmp/data/test2.h
        -$(QINSTALL) /tmp/test/src/test3.h $(INSTALL_ROOT)/tmp/data/test3.h

The '/tmp/test/src' path seems to be based on the .pro file and not based on my shadow directory location. How do I force that path to be in '/tmp/test/shadow' instead? Is this a bug in qmake?

I tried 'gen_headers.output = $$OUT_PWD/${QMAKE_FILE_BASE}.h' but that did not change anything.