qt6_wrap_cpp: Add .moc generation

When a `.moc` file is included in a source file and that source passed
to `qt_wrap_cpp`, Users should add the generated `.moc`s path to the
target's  include path. Since we don't share anything about the output
path of generated files by `qt_wrap_cpp`, it makes sense to add in
inside `qt_wrap_cpp`. And also, the generated `.moc` file is added
to target's source to complete the dependency graph. Otherwise, Users
need to get output variable and pass it to target's sources.

* Update docs
* Add test

[ChangeLog][Build System] qt_wrap_cpp will accept .cpp files from now
on. When .cpp a file is passed to qt_wrap_cpp, TARGET parameter
becomes required. Generated .moc files are added to target's sources
inside qt_wrap_cpp. That's why the output parameter will not contain
generated .moc files.

Fixes: QTBUG-113402
Change-Id: I54dd2b1ff8e5c9ba457b1eb4f73b0a8190d9c659
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

3 files changed, 39 insertions, 1 deletions

diff --git a/src/corelib/doc/snippets/cmake-macros/examples.cmake b/src/corelib/doc/snippets/cmake-macros/examples.cmake
index c8d5e71081..b0800d8fe0 100644
--- a/src/corelib/doc/snippets/cmake-macros/examples.cmake
+++ b/src/corelib/doc/snippets/cmake-macros/examples.cmake
@@ -28,6 +28,11 @@ target_compile_definitions(myapp PRIVATE "$<$<CONFIG:Debug>:MY_OPTION_FOR_DEBUG>
                                          "$<$<BOOL:TRUE>:DEFINE_CMDLINE_SIGNAL_IN_GENEX=void cmdlineSignal(const QMap<int$<COMMA> int$<ANGLE-R> &i)>")
 #! [qt_wrap_cpp_3]
 
+#! [qt_wrap_cpp_4]
+qt_add_executable(myapp myapp.cpp main.cpp)
+qt_wrap_cpp("" myapp.cpp TARGET myapp)
+#! [qt_wrap_cpp_4]
+
 #! [qt_add_resources]
 set(SOURCES main.cpp)
 qt_add_resources(SOURCES example.qrc)
diff --git a/src/corelib/doc/snippets/cmake-macros/examples.cpp b/src/corelib/doc/snippets/cmake-macros/examples.cpp
new file mode 100644
index 0000000000..b17fcd8e77
--- /dev/null
+++ b/src/corelib/doc/snippets/cmake-macros/examples.cpp
@@ -0,0 +1,16 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+//! [qt_wrap_cpp_4]
+// myapp.cpp
+#include "myapp.h"
+#include <QObject>
+
+class MyApp : public QObject {
+    Q_OBJECT
+public:
+    MyApp() = default;
+};
+
+#include "myapp.moc"
+//! [qt_wrap_cpp_4]
diff --git a/src/corelib/doc/src/cmake/qt_wrap_cpp.qdoc b/src/corelib/doc/src/cmake/qt_wrap_cpp.qdoc
index 0624651869..3b298a9d7e 100644
--- a/src/corelib/doc/src/cmake/qt_wrap_cpp.qdoc
+++ b/src/corelib/doc/src/cmake/qt_wrap_cpp.qdoc
@@ -40,6 +40,12 @@ You can set an explicit \c{TARGET}. This will make sure that the target
 properties \c{INCLUDE_DIRECTORIES} and \c{COMPILE_DEFINITIONS} are also used
 when scanning the source files with \c{moc}.
 
+Since Qt 6.8, when a source file is passed to \c{qt_wrap_cpp} instead of a
+header file to generate a \c{.moc} file for a target, the \c{TARGET} parameter
+is needed to set the correct include path for the generated \c{.moc} file in
+the source file. As generated \c{.moc} files are added to the target's
+sources by \c{qt_wrap_cpp}, they are not added to \c{<VAR>}.
+
 You can set additional \c{OPTIONS} that should be added to the \c{moc} calls.
 You can find possible options in the \l{moc}{moc documentation}.
 
@@ -69,5 +75,16 @@ avoid syntax errors in the generator expressions.
 The following example uses \l{https://cmake.org/cmake/help/latest/command/target_compile_definitions.html}{target_compile_definitions}
 to set \l{https://cmake.org/cmake/help/latest/prop_tgt/COMPILE_DEFINITIONS.html}{COMPILE_DEFINITIONS} which will be added to
 \c{OPTIONS}.
-\snippet cmake-macros/examples.cmake qt_wrap_cpp_3
+
+\snippet cmake-macros/examples.cmake qt_wrap_cpp_4
+
+\snippet cmake-macros/examples.cpp qt_wrap_cpp_4
+
+In the above file, \c{myapp.moc} is included in \c{myapp.cpp}.
+To generate the \c{myapp.moc} file, the \c{qt_wrap_cpp} macro is used with the
+\c{TARGET} parameter. The first parameter is empty because the \c{.moc} file
+and its path will be added to the target's sources and include directories by
+the \c{qt_wrap_cpp} macro.
+
+\snippet cmake-macros/examples.cmake qt_wrap_cpp_4
 */