CMake: Fix generation of prl files for non-qtbase modules

Previously we determined if a library represented by an absolute path
is a Qt module by checking if it's located in the build dir of the
current repo.

That is not sufficient for non-qtbase prefix builds, where
a Qt module might link against both a module in the current
build dir and in the prefix dir.

Detect such cases, and rewrite the absolute paths to relocatable paths
(either framework flags or paths starting with $$[QT_INSTALL_LIBS].

This should fix building examples with qmake that use QtQuick.

Fixes: QTBUG-87840
Change-Id: Icaf8f1a7c66292c80662fd0d5771a5a1628a9899
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

3 files changed, 47 insertions, 6 deletions

diff --git a/cmake/QtFinishPrlFile.cmake b/cmake/QtFinishPrlFile.cmake
index 93fd558bab..7de3bd48f3 100644
--- a/cmake/QtFinishPrlFile.cmake
+++ b/cmake/QtFinishPrlFile.cmake
@@ -7,13 +7,15 @@
 #   aka from "/usr/lib/x86_64-linux-gnu/libcups.so" to "-lcups"
 # - Replaces Qt absolute framework paths into a combination of -F$$[QT_INSTALL_LIBS] and
 #   -framework QtFoo
-# - Prepends '-l' to values that are not absolute paths, and don't start with either '-l' or
-#   '-framework'.
+# - Prepends '-l' to values that are not absolute paths, and don't start with a dash
+#   aka, '-lfoo', '-framework', '-pthread'.
 #
 # This file is to be used in CMake script mode with the following variables set:
 # IN_FILE: path to the preliminary .prl file
 # OUT_FILE: path to the final .prl file that's going to be installed
-# QT_BUILD_LIBDIR: path to Qt's libdir when building (those paths get replaced)
+# QT_LIB_DIRS: list of paths where Qt libraries are located.
+#              This includes the install prefix and the current repo build dir.
+#              These paths get replaced with relocatable paths or linker / framework flags.
 # LIBRARY_SUFFIXES: list of known library extensions, e.g. .so;.a on Linux
 # LIBRARY_PREFIXES: list of known library prefies, e.g. the "lib" in "libz" on on Linux
 # LINK_LIBRARY_FLAG: flag used to link a shared library to an executable, e.g. -l on UNIX
@@ -32,12 +34,19 @@ foreach(line ${lines})
             if("${lib}" STREQUAL "")
                 continue()
             endif()
+
+            # Check if the absolute path represents a Qt module located either in Qt's
+            # $prefix/lib dir, or in the build dir of the repo.
             if(IS_ABSOLUTE "${lib}")
-                file(RELATIVE_PATH relative_lib "${QT_BUILD_LIBDIR}" "${lib}")
-                if(IS_ABSOLUTE "${relative_lib}" OR (relative_lib MATCHES "^\\.\\."))
+                qt_internal_path_is_relative_to_qt_lib_path(
+                    "${lib}" "${QT_LIB_DIRS}" lib_is_a_qt_module relative_lib)
+                if(NOT lib_is_a_qt_module)
+                    # It's not a Qt module, extract the library name and prepend an -l to make
+                    # it relocatable.
                     qt_transform_absolute_library_paths_to_link_flags(lib_with_link_flag "${lib}")
                     list(APPEND adjusted_libs "${lib_with_link_flag}")
                 else()
+                    # Is a Qt module.
                     # Transform Qt framework paths into -framework flags.
                     if(relative_lib MATCHES "^(Qt(.+))\\.framework/")
                         if(NOT qt_framework_search_path_inserted)
@@ -46,11 +55,14 @@ foreach(line ${lines})
                         endif()
                         list(APPEND adjusted_libs "-framework" "${CMAKE_MATCH_1}")
                     else()
+                        # Not a framework, transform the Qt module into relocatable relative path.
                         qt_strip_library_version_suffix(relative_lib "${relative_lib}")
                         list(APPEND adjusted_libs "$$[QT_INSTALL_LIBS]/${relative_lib}")
                     endif()
                 endif()
             else()
+                # Not absolute path, most likely a library name or a linker flag.
+                # If linker flag (like -framework, -lfoo, -pthread, keep it as-is).
                 if(NOT lib MATCHES "^-")
                     string(PREPEND lib "-l")
                 endif()
diff --git a/cmake/QtGenerateLibHelpers.cmake b/cmake/QtGenerateLibHelpers.cmake
index 06de484ac4..dedcdc7950 100644
--- a/cmake/QtGenerateLibHelpers.cmake
+++ b/cmake/QtGenerateLibHelpers.cmake
@@ -88,3 +88,26 @@ function(qt_strip_library_version_suffix out_var file_path)
     endif()
     set(${out_var} "${final_value}" PARENT_SCOPE)
 endfunction()
+
+# Checks if `input_path` is relative to at least one path given in the list of `qt_lib_paths`.
+# Sets TRUE or FALSE in `out_var_is_relative`.
+# Assigns the relative path to `out_var_relative_path` if the path is relative, otherwise assigns
+# the original path.
+function(qt_internal_path_is_relative_to_qt_lib_path
+        input_path qt_lib_paths out_var_is_relative out_var_relative_path)
+    set(is_relative "FALSE")
+    set(relative_path_value "${input_path}")
+
+    foreach(qt_lib_path ${qt_lib_paths})
+        file(RELATIVE_PATH relative_path "${qt_lib_path}" "${input_path}")
+        if(IS_ABSOLUTE "${relative_path}" OR (relative_path MATCHES "^\\.\\."))
+            set(is_relative "FALSE")
+        else()
+            set(is_relative "TRUE")
+            set(relative_path_value "${relative_path}")
+            break()
+        endif()
+    endforeach()
+    set(${out_var_is_relative} "${is_relative}" PARENT_SCOPE)
+    set(${out_var_relative_path} "${relative_path_value}" PARENT_SCOPE)
+endfunction()
diff --git a/cmake/QtPrlHelpers.cmake b/cmake/QtPrlHelpers.cmake
index 932565f318..35d321420c 100644
--- a/cmake/QtPrlHelpers.cmake
+++ b/cmake/QtPrlHelpers.cmake
@@ -270,6 +270,12 @@ QMAKE_PRL_VERSION = ${PROJECT_VERSION}
         set(configs ${CMAKE_BUILD_TYPE})
     endif()
 
+    set(qt_lib_dirs "${QT_BUILD_DIR}/${INSTALL_LIBDIR}")
+    if(QT_WILL_INSTALL)
+        list(APPEND qt_lib_dirs
+             "${QT_BUILD_INTERNALS_RELOCATABLE_INSTALL_PREFIX}/${INSTALL_LIBDIR}")
+    endif()
+
     foreach(config ${configs})
         # Output file for dependency tracking, and which will contain the final content.
         qt_path_join(prl_step2_path
@@ -296,7 +302,7 @@ QMAKE_PRL_VERSION = ${PROJECT_VERSION}
                     "-DLIBRARY_PREFIXES=${library_prefixes}"
                     "-DLIBRARY_SUFFIXES=${library_suffixes}"
                     "-DLINK_LIBRARY_FLAG=${CMAKE_LINK_LIBRARY_FLAG}"
-                    "-DQT_BUILD_LIBDIR=${QT_BUILD_DIR}/${INSTALL_LIBDIR}"
+                    "-DQT_LIB_DIRS=${qt_lib_dirs}"
                     -P "${QT_CMAKE_DIR}/QtFinishPrlFile.cmake"
             VERBATIM
             COMMENT "Generating prl file for target ${target}"