qt-compatibility-build

name	qt-compatibility-build
description	Use when maintaining Debian packages that need Qt5/Qt6 dual support, CMakeLists.txt has hard-coded Qt5/Qt6 or DTK5/DTK6 versions, or projects need dynamic library linking based on detected Qt version for deepin V25/V20 compatibility

qt-compatibility-build

Overview

Unifies CMake configuration for deepin V25/V20 dual-version support by automatically detecting Qt5/Qt6 and dynamically mapping DTK versions, eliminating hard-coded version references throughout the build system.

File Convention

File	Deepin Version	Qt Version
debian/control	V25	Qt6
debian/control.1	V20	Qt5

Why: control (no suffix) = latest version (V25), control.1 (with suffix) = previous version (V20).

When to Use

digraph when_to_use {
    "Qt/CMake project?" [shape=diamond];
    "V25/V20 dual support?" [shape=diamond];
    "Hard-coded Qt/DTK?" [shape=diamond];
    "Use this skill" [shape=box];
    "Wrong tool" [shape=box];

    "Qt/CMake project?" -> "V25/V20 dual support?" [label="yes"];
    "V25/V20 dual support?" -> "Hard-coded Qt/DTK?" [label="yes"];
    "Hard-coded Qt/DTK?" -> "Use this skill" [label="yes"];
}

Use when:

• CMakeLists.txt has hard-coded Qt5:: or Qt6:: in target_link_libraries
• CMakeLists.txt has hard-coded Dtk:: or Dtk6:: in find_package or linking
• Projects need both V25 (Qt6) and V20 (Qt5) builds from same code
• Need dynamic library linking based on detected Qt version
• DTK dependencies need to map automatically to installed Qt version

Do NOT use when:

• Projects without CMake build system
• Projects without Qt dependencies
• Single version support only (V25-only or V20-only)

Quick Reference

Task	Command/Pattern
Auto-detect Qt	find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Core)
Map DTK to Qt	if (QT_VERSION_MAJOR MATCHES 6) set(DTK_VERSION_MAJOR 6)
Dynamic Qt find	find_package(Qt${QT_VERSION_MAJOR} COMPONENTS ${QT} REQUIRED)
Dynamic DTK find	find_package(Dtk${DTK_VERSION_MAJOR}Widget REQUIRED)
Dynamic Qt linking	Qt${QT_VERSION_MAJOR}::Core
Dynamic DTK linking	Dtk${DTK_VERSION_MAJOR}::Core
V25 build	cmake -B build -DQT_DIR=/usr/lib/x86_64-linux-gnu/cmake/Qt6
V20 build	cmake -B build5 -DQT_DIR=/usr/lib/x86_64-linux-gnu/cmake/Qt5

Note: -DQT_DIR is optional for local build convenience. CMake auto-detects if not specified.

Implementation

Step 1: Add Qt Detection (CMakeLists.txt top)

# Auto-detect Qt version (tries Qt6 first, falls back to Qt5)
find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Core)
message(STATUS "Found Qt version: ${QT_VERSION_MAJOR}")

# Map to DTK version (Qt6→DTK6, Qt5→DTK5)
if (QT_VERSION_MAJOR MATCHES 6)
    set(DTK_VERSION_MAJOR 6)
else()
    set(DTK_VERSION_MAJOR "")
endif()
message(STATUS "Build with DTK: ${DTK_VERSION_MAJOR}")

Step 2: Update All find_package Calls

Before (hard-coded):

find_package(Qt6 COMPONENTS Core Gui Widgets Network REQUIRED)
find_package(DtkWidget REQUIRED)

After (dynamic):

set(QT Core Gui Widgets Network DBus Sql Svg Test WebChannel WebSockets)
find_package(Qt${QT_VERSION_MAJOR} COMPONENTS ${QT} REQUIRED)

find_package(Dtk${DTK_VERSION_MAJOR}Widget REQUIRED)
find_package(Dtk${DTK_VERSION_MAJOR}Core REQUIRED)
find_package(Dtk${DTK_VERSION_MAJOR}Gui REQUIRED)

Step 3: Update All target_link_libraries

Before (hard-coded):

target_link_libraries(mylib
    Dtk::Core
    Dtk::Gui
    Qt6::Network
)

After (dynamic):

target_link_libraries(mylib
    Dtk${DTK_VERSION_MAJOR}::Core
    Dtk${DTK_VERSION_MAJOR}::Gui
    Qt${QT_VERSION_MAJOR}::Network
)

Replacement pattern:

• Qt5:: → Qt${QT_VERSION_MAJOR}::
• Qt6:: → Qt${QT_VERSION_MAJOR}::
• Dtk:: → Dtk${DTK_VERSION_MAJOR}::
• Dtk6:: → Dtk${DTK_VERSION_MAJOR}::

Step 4: Translation Generation (if needed)

Create cmake/translation-generate.cmake:

function(TRANSLATION_GENERATE QMS)
  find_package(Qt${QT_VERSION_MAJOR}LinguistTools QUIET)

  if (NOT Qt${QT_VERSION_MAJOR}_LRELEASE_EXECUTABLE)
    set(QT_LRELEASE "/lib/qt${QT_VERSION_MAJOR}/bin/lrelease")
    message(STATUS "NOT found lrelease, set QT_LRELEASE = ${QT_LRELEASE}")
  else()
    set(QT_LRELEASE "${Qt${QT_VERSION_MAJOR}_LRELEASE_EXECUTABLE}")
  endif()

  if(NOT ARGN)
    message(SEND_ERROR "Error: TRANSLATION_GENERATE() called without any .ts path")
    return()
  endif()

  file(GLOB TS_FILES "${ARGN}/*.ts")
  set(${QMS})
  foreach(TSFIL ${TS_FILES})
      get_filename_component(FIL_WE ${TSFIL} NAME_WE)
      set(QMFIL ${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}.qm)
      list(APPEND ${QMS} ${QMFIL})
      add_custom_command(
          OUTPUT ${QMFIL}
          COMMAND ${QT_LRELEASE} ${TSFIL} -qm ${QMFIL}
          DEPENDS ${TSFIL}
          COMMENT "Running ${QT_LRELEASE} on ${TSFIL}"
          VERBATIM
      )
  endforeach()

  set_source_files_properties(${${QMS}} PROPERTIES GENERATED TRUE)
  set(${QMS} ${${QMS}} PARENT_SCOPE)
endfunction()

Usage:

include(translation-generate)
TRANSLATION_GENERATE(QM_FILES ${CMAKE_SOURCE_DIR}/translations)
add_custom_target(${PROJECT_NAME}_qm_files DEPENDS ${QM_FILES})
add_dependencies(${PROJECT_NAME} ${PROJECT_NAME}_qm_files)
install(FILES ${QM_FILES} DESTINATION share/${PROJECT_NAME}/translations)

Step 5: Create Control Files

debian/control (V25/Qt6):

Build-Depends:
 cmake,
 pkg-config,
 qt6-base-dev,
 qt6-tools-dev,
 qt6-svg-dev,
 libdtk6widget-dev,
 libdtk6core-dev

debian/control.1 (V20/Qt5):

Build-Depends:
 cmake,
 pkg-config,
 qtbase5-dev,
 qttools5-dev,
 libqt5svg5-dev,
 libdtkwidget-dev,
 libdtkcore-dev

Dependency Mapping

Purpose	V25 (Qt6)	V20 (Qt5)
Base	qt6-base-dev	qtbase5-dev
Tools	qt6-tools-dev	qttools5-dev
SVG	qt6-svg-dev	libqt5svg5-dev
DTK Widget	libdtk6widget-dev	libdtkwidget-dev
DTK Core	libdtk6core-dev	libdtkcore-dev

Common Mistakes

Mistake	Why It's Wrong	Fix
Hard-coded Qt5::Core / Qt6::Core	Forces specific Qt version	Use Qt${QT_VERSION_MAJOR}::Core
Hard-coded Dtk::Core / Dtk6::Core	Forces specific DTK version	Use Dtk${DTK_VERSION_MAJOR}::Core
Missing DTK_VERSION_MAJOR	DTK won't map to Qt version	Add variable mapping from Qt detection
Only using control without control.1	Won't support V20	Create both control files
Using OR dependencies in single control	Should use separate files	Split into control and control.1
Only testing one Qt version	Both must work for dual support	Test V25 and V20 builds
Not using find_package(QT NAMES Qt6 Qt5 ...)	Won't auto-detect both	Use correct find_package pattern

Red Flags - STOP and Check

• Hard-coded Qt5/Qt6 in CMakeLists.txt → Must use QT_VERSION_MAJOR variable
• Hard-coded DTK5/DTK6 in CMakeLists.txt → Must use DTK_VERSION_MAJOR variable
• Missing DTK_VERSION_MAJOR variable → DTK won't map to Qt version
• Using OR dependencies instead of separate control files → Should use control/control.1
• Only testing one Qt version → Both versions must work
• Qt detection not using find_package(QT NAMES Qt6 Qt5 ...) → Won't detect both versions