ENH: Support version argument in find_package().

      See bug #8542.

Modules/FindQt4.cmake

@@ -372,6 +372,18 @@ IF (QT_QMAKE_EXECUTABLE)
     STRING(REGEX REPLACE "^[0-9]+\\.([0-9])+\\.[0-9]+" "\\1" req_qt_minor_vers "${QT_MIN_VERSION}")
     STRING(REGEX REPLACE "^[0-9]+\\.[0-9]+\\.([0-9]+)" "\\1" req_qt_patch_vers "${QT_MIN_VERSION}")
 
+  # Suppport finding at least a particular version, for instance FIND_PACKAGE( Qt4 4.4.3 )
+  # This implementation is a hack to avoid duplicating code and make sure we stay
+  # source-compatible with CMake 2.6.x
+  # For CMake 2.8, we should not set QT_MIN_VERSION but only use Qt4_FIND_VERSION_MAJOR,
+  # Qt4_FIND_VERSION_MINOR, etc
+  IF( Qt4_FIND_VERSION )
+    SET( QT_MIN_VERSION ${Qt4_FIND_VERSION} )
+    SET( req_qt_major_vers ${Qt4_FIND_VERSION_MAJOR} )
+    SET( req_qt_minor_vers ${Qt4_FIND_VERSION_MINOR} )
+    SET( req_qt_patch_vers ${Qt4_FIND_VERSION_PATCH} )
+  ENDIF( Qt4_FIND_VERSION )
+
     IF (NOT req_qt_major_vers EQUAL 4)
       MESSAGE( FATAL_ERROR "Invalid Qt version string given: \"${QT_MIN_VERSION}\", major version 4 is required, e.g. \"4.0.1\"")
     ENDIF (NOT req_qt_major_vers EQUAL 4)
@@ -385,12 +397,27 @@ IF (QT_QMAKE_EXECUTABLE)
     MATH(EXPR req_vers "${req_qt_major_vers}*10000 + ${req_qt_minor_vers}*100 + ${req_qt_patch_vers}")
     MATH(EXPR found_vers "${QT_VERSION_MAJOR}*10000 + ${QT_VERSION_MINOR}*100 + ${QT_VERSION_PATCH}")
 
+  # Support finding *exactly* a particular version, for instance FIND_PACKAGE( Qt4 4.4.3 EXACT )
+  # The 'else' branch should be removed for CMake 2.8
+  IF( Qt4_FIND_VERSION_EXACT )
+    IF(found_vers EQUAL req_vers)
+      SET( QT4_QMAKE_FOUND TRUE )
+    ELSE(found_vers EQUAL req_vers)
+      SET( QT4_QMAKE_FOUND FALSE )
+      IF (found_vers LESS req_vers)
+        SET(QT4_INSTALLED_VERSION_TOO_OLD TRUE)
+      ELSE (found_vers LESS req_vers)
+        SET(QT4_INSTALLED_VERSION_TOO_NEW TRUE)
+      ENDIF (found_vers LESS req_vers)
+    ENDIF(found_vers EQUAL req_vers)
+  ELSE( Qt4_FIND_VERSION_EXACT )
     IF (found_vers LESS req_vers)
       SET(QT4_QMAKE_FOUND FALSE)
       SET(QT4_INSTALLED_VERSION_TOO_OLD TRUE)
     ELSE (found_vers LESS req_vers)
       SET(QT4_QMAKE_FOUND TRUE)
     ENDIF (found_vers LESS req_vers)
+  ENDIF( Qt4_FIND_VERSION_EXACT )
   ENDIF (qt_version_tmp)
 
 ENDIF (QT_QMAKE_EXECUTABLE)
@@ -1550,11 +1577,23 @@ IF (QT4_QMAKE_FOUND)
 ELSE(QT4_QMAKE_FOUND)
    
    SET(QT_QMAKE_EXECUTABLE "${QT_QMAKE_EXECUTABLE}-NOTFOUND" CACHE FILEPATH "Invalid qmake found" FORCE)
+   
+   # The code below is overly complex to make sure we do not break compatibility with CMake 2.6.x
+   # For CMake 2.8, it should be simplified by getting rid of QT4_INSTALLED_VERSION_TOO_OLD and 
+   # QT4_INSTALLED_VERSION_TOO_NEW
    IF(Qt4_FIND_REQUIRED)
       IF(QT4_INSTALLED_VERSION_TOO_OLD)
-         MESSAGE(FATAL_ERROR "The installed Qt version ${QTVERSION} is too old, at least version ${QT_MIN_VERSION} is required")
+    IF( Qt4_FIND_VERSION_EXACT )
+      MESSAGE(FATAL_ERROR "The installed Qt version ${QTVERSION} is too old, version ${QT_MIN_VERSION} is required")
+    ELSE( Qt4_FIND_VERSION_EXACT )
+      MESSAGE(FATAL_ERROR "The installed Qt version ${QTVERSION} is too old, at least version ${QT_MIN_VERSION} is required")
+    ENDIF( Qt4_FIND_VERSION_EXACT )
       ELSE(QT4_INSTALLED_VERSION_TOO_OLD)
-         MESSAGE( FATAL_ERROR "Qt qmake not found!")
+      IF( Qt4_FIND_VERSION_EXACT AND QT4_INSTALLED_VERSION_TOO_NEW )
+      MESSAGE(FATAL_ERROR "The installed Qt version ${QTVERSION} is too new, version ${QT_MIN_VERSION} is required")
+    ELSE( Qt4_FIND_VERSION_EXACT AND QT4_INSTALLED_VERSION_TOO_NEW )
+      MESSAGE( FATAL_ERROR "Qt qmake not found!")
+    ENDIF( Qt4_FIND_VERSION_EXACT AND QT4_INSTALLED_VERSION_TOO_NEW )
       ENDIF(QT4_INSTALLED_VERSION_TOO_OLD)
    ELSE(Qt4_FIND_REQUIRED)
       IF(QT4_INSTALLED_VERSION_TOO_OLD AND NOT Qt4_FIND_QUIETLY)