cmake: Add warnings_are_errors option

for modules, plugins and tools only (i.e. no tests nor examples)
this mimics the qmake behavior

default value is developer_build

Comes with some fixes in qmake since it seems in the qmake built it was
not having Werror, now does because we built it with add_qt_tool

Change-Id: I6f3237f25a6fedefa958644929e90f13837a12df
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

7 files changed, 76 insertions, 4 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8344d22c0d..6be7a6edcb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -35,6 +35,9 @@ include(QtBaseGlobalTargets)
 option(BUILD_SHARED_LIBS "Build Qt statically or dynamically" ON)
 set(QT_BUILD_SHARED_LIBS ${BUILD_SHARED_LIBS})
 
+## Should this Qt be built with Werror?
+option(WARNINGS_ARE_ERRORS "Build Qt with warnings as errors" ${FEATURE_developer_build})
+
 ## Decide whether tools will be built.
 qt_check_if_tools_will_be_built()
 
diff --git a/cmake/QtBuild.cmake b/cmake/QtBuild.cmake
index acc36276bb..08b04e42ea 100644
--- a/cmake/QtBuild.cmake
+++ b/cmake/QtBuild.cmake
@@ -1002,6 +1002,60 @@ function(qt_internal_set_no_exceptions_flags target)
     endif()
 endfunction()
 
+function(qt_internal_set_warnings_are_errors_flags target)
+    if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+        # Regular clang 3.0+
+        if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "3.0.0")
+            target_compile_options("${target}" PRIVATE -Werror -Wno-error=\#warnings -Wno-error=deprecated-declarations)
+        endif()
+    elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "AppleClang")
+        # using AppleClang
+        # Apple clang 4.0+
+        if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "4.0.0")
+            target_compile_options("${target}" PRIVATE -Werror -Wno-error=\#warnings -Wno-error=deprecated-declarations)
+        endif()
+    elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
+        # using GCC
+        target_compile_options("${target}" PRIVATE -Werror -Wno-error=cpp -Wno-error=deprecated-declarations)
+
+        # GCC prints this bogus warning, after it has inlined a lot of code
+        # error: assuming signed overflow does not occur when assuming that (X + c) < X is always false
+        target_compile_options("${target}" PRIVATE -Wno-error=strict-overflow)
+
+        # GCC 7 includes -Wimplicit-fallthrough in -Wextra, but Qt is not yet free of implicit fallthroughs.
+        if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "7.0.0")
+            target_compile_options("${target}" PRIVATE -Wno-error=implicit-fallthrough)
+        endif()
+
+        if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "9.0.0")
+            # GCC 9 introduced these but we are not clean for it.
+            target_compile_options("${target}" PRIVATE -Wno-error=deprecated-copy -Wno-error=redundant-move -Wno-error=init-list-lifetime)
+        endif()
+
+        # Work-around for bug https://code.google.com/p/android/issues/detail?id=58135
+        if (ANDROID)
+            target_compile_options("${target}" PRIVATE -Wno-error=literal-suffix)
+        endif()
+    elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Intel")
+        # Intel CC 13.0 +, on Linux only
+        if (LINUX)
+            if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "13.0.0")
+                # 177: function "entity" was declared but never referenced
+                #      (too aggressive; ICC reports even for functions created due to template instantiation)
+                # 1224: #warning directive
+                # 1478: function "entity" (declared at line N) was declared deprecated
+                # 1786: function "entity" (declared at line N of "file") was declared deprecated ("message")
+                # 1881: argument must be a constant null pointer value
+                #      (NULL in C++ is usually a literal 0)
+                target_compile_options("${target}" PRIVATE -Werror -ww177,1224,1478,1786,1881)
+            endif()
+        endif()
+    elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
+        # using Visual Studio C++
+        target_compile_options("${target}" PRIVATE /WX)
+    endif()
+endfunction()
+
 # This is the main entry function for creating a Qt module, that typically
 # consists of a library, public header files, private header files and configurable
 # features.
@@ -1146,6 +1200,9 @@ function(add_qt_module target)
     if(NOT ${arg_EXCEPTIONS})
         qt_internal_set_no_exceptions_flags("${target}")
     endif()
+    if(WARNINGS_ARE_ERRORS)
+        qt_internal_set_warnings_are_errors_flags("${target}")
+    endif()
 
     set(configureFile "${CMAKE_CURRENT_SOURCE_DIR}/configure.cmake")
     if(EXISTS "${configureFile}")
@@ -1478,6 +1535,9 @@ function(add_qt_plugin target)
     if(NOT ${arg_EXCEPTIONS})
         qt_internal_set_no_exceptions_flags("${target}")
     endif()
+    if(WARNINGS_ARE_ERRORS)
+        qt_internal_set_warnings_are_errors_flags("${target}")
+    endif()
 
 
     set(qt_libs_private "")
@@ -1777,6 +1837,9 @@ function(add_qt_tool name)
         DISABLE_AUTOGEN_TOOLS ${disable_autogen_tools}
     )
     qt_internal_add_target_aliases("${name}")
+    if(WARNINGS_ARE_ERRORS)
+        qt_internal_set_warnings_are_errors_flags("${name}")
+    endif()
 
     if(NOT arg_NO_INSTALL AND arg_TOOLS_TARGET)
         # Assign a tool to an export set, and mark the module to which the tool belongs.
diff --git a/qmake/generators/mac/pbuilder_pbx.cpp b/qmake/generators/mac/pbuilder_pbx.cpp
index b3c6ba4869..59a4008a3b 100644
--- a/qmake/generators/mac/pbuilder_pbx.cpp
+++ b/qmake/generators/mac/pbuilder_pbx.cpp
@@ -513,7 +513,6 @@ bool
 ProjectBuilderMakefileGenerator::writeMakeParts(QTextStream &t)
 {
     ProStringList tmp;
-    bool did_preprocess = false;
 
     //HEADER
     const int pbVersion = pbuilderVersion();
@@ -731,7 +730,6 @@ ProjectBuilderMakefileGenerator::writeMakeParts(QTextStream &t)
         QFile mkf(mkfile);
         if(mkf.open(QIODevice::WriteOnly | QIODevice::Text)) {
             writingUnixMakefileGenerator = true;
-            did_preprocess = true;
             debug_msg(1, "pbuilder: Creating file: %s", mkfile.toLatin1().constData());
             QTextStream mkt(&mkf);
             writeHeader(mkt);
diff --git a/qmake/generators/makefile.cpp b/qmake/generators/makefile.cpp
index f3ca192ab2..411bb37437 100644
--- a/qmake/generators/makefile.cpp
+++ b/qmake/generators/makefile.cpp
@@ -895,6 +895,7 @@ bool
 MakefileGenerator::processPrlFileBase(QString &origFile, const QStringRef &origName,
                                       const QStringRef &fixedBase, int slashOff)
 {
+    Q_UNUSED(slashOff)
     return processPrlFileCore(origFile, origName, fixedBase + Option::prl_ext);
 }
 
diff --git a/qmake/generators/projectgenerator.h b/qmake/generators/projectgenerator.h
index e9b050cc74..ef6a76f0d0 100644
--- a/qmake/generators/projectgenerator.h
+++ b/qmake/generators/projectgenerator.h
@@ -43,7 +43,7 @@ protected:
     void init() override;
     bool writeMakefile(QTextStream &) override;
 
-    QString escapeFilePath(const QString &path) const override { Q_ASSERT(false); return QString(); }
+    QString escapeFilePath(const QString &path) const override { Q_UNUSED(path); Q_ASSERT(false); return QString(); }
 
 public:
     bool supportsMetaBuild() override { return false; }
diff --git a/qmake/generators/win32/winmakefile.cpp b/qmake/generators/win32/winmakefile.cpp
index 8e0c62e13f..b79fd8f250 100644
--- a/qmake/generators/win32/winmakefile.cpp
+++ b/qmake/generators/win32/winmakefile.cpp
@@ -645,7 +645,7 @@ void Win32MakefileGenerator::writeObjectsPart(QTextStream &t)
     t << "OBJECTS       = " << valList(escapeDependencyPaths(project->values("OBJECTS"))) << Qt::endl;
 }
 
-void Win32MakefileGenerator::writeImplicitRulesPart(QTextStream &t)
+void Win32MakefileGenerator::writeImplicitRulesPart(QTextStream &)
 {
 }
 
diff --git a/src/gui/CMakeLists.txt b/src/gui/CMakeLists.txt
index b662f8e092..fe37e4daa5 100644
--- a/src/gui/CMakeLists.txt
+++ b/src/gui/CMakeLists.txt
@@ -36,6 +36,13 @@ if (QT_FEATURE_gui)
 
     set(QT_QPA_DEFAULT_PLATFORM "${_default_platform}" CACHE STRING "QPA default platform")
 endif()
+
+if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
+    set_source_files_properties(../3rdparty/md4c/md4c.c PROPERTIES COMPILE_FLAGS "-Wno-error=unused-parameter -Wno-error=sign-compare -Wno-error=missing-field-initializers")
+elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+    set_source_files_properties(../3rdparty/md4c/md4c.c PROPERTIES COMPILE_FLAGS "-Wno-error=unused-parameter -Wno-error=sign-compare -Wno-error=missing-field-initializers -Wno-error=missing-braces")
+endif()
+
 # special case end
 
 add_qt_module(Gui