Add the infrastructure to compile Qt with -Werror

This is enabled only for -developer-builds and only for certain
compiler-version combinations that are in a whitelist.

It also requires each library, plugin or tool to declare whether it is
supposedly clean of warnings. When most targets are clean, we can
consider inverting.

Change-Id: I17b5c4e45aee5078f9788e846a45d619c144095a
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

3 files changed, 69 insertions, 2 deletions

diff --git a/configure b/configure
index dbc82b4e47..777de4673e 100755
--- a/configure
+++ b/configure
@@ -2,6 +2,7 @@
 #############################################################################
 ##
 ## Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
+## Copyright (C) 2013 Intel Corporation.
 ## Contact: http://www.qt-project.org/legal
 ##
 ## This file is the build configuration utility of the Qt Toolkit.
@@ -893,6 +894,7 @@ CFG_PCRE=auto
 QPA_PLATFORM_GUARD=yes
 CFG_CXX11=auto
 CFG_DIRECTWRITE=no
+CFG_WERROR=auto
 
 # initalize variables used for installation
 QT_INSTALL_PREFIX=
@@ -2138,6 +2140,13 @@ while [ "$#" -gt 0 ]; do
             UNKNOWN_OPT=yes
         fi
         ;;
+    warnings-are-errors|Werror)
+        if [ "$VAL" = "yes" ] || [ "$VAL" = "no" ]; then
+            CFG_WERROR="$VAL"
+        else
+            UNKNOWN_OPT=yes
+        fi
+        ;;
     *)
         UNKNOWN_OPT=yes
         ;;
@@ -3296,6 +3305,10 @@ Additional options:
  *  -no-system-proxies .. Do not use system network proxies by default.
     -system-proxies ..... Use system network proxies by default.
 
+    -no-warnings-are-errors Make warnings be treated normally
+    -warnings-are-errors  Make warnings be treated as errors
+                          (enabled if -developer-build is active)
+
  $GBN  -no-glib ........... Do not compile Glib support.
  $GBY  -glib .............. Compile Glib support.
 EOF
@@ -6098,6 +6111,11 @@ else
 fi
 if [ "$CFG_DEV" = "yes" ]; then
     QT_CONFIG="$QT_CONFIG private_tests"
+    if [ "$CFG_WERROR" != "no" ]; then
+        QMAKE_CONFIG="$QMAKE_CONFIG warnings_are_errors"
+    fi
+elif [ "$CFG_WERROR" = "yes" ]; then
+    QMAKE_CONFIG="$QMAKE_CONFIG warnings_are_errors"
 fi
 
 cat >>"$QTCONFIG.tmp" <<EOF
diff --git a/mkspecs/features/qt_common.prf b/mkspecs/features/qt_common.prf
index 2400ab0c2c..10b7736749 100644
--- a/mkspecs/features/qt_common.prf
+++ b/mkspecs/features/qt_common.prf
@@ -18,3 +18,37 @@ contains(TEMPLATE, .*lib) {
     contains(QT_CONFIG, separate_debug_info): CONFIG += separate_debug_info
     contains(QT_CONFIG, separate_debug_info_nocopy): CONFIG += separate_debug_info_nocopy
 }
+
+warnings_are_errors:warning_clean {
+    # If the module declares that it has does its clean-up of warnings, enable -Werror.
+    # This setting is compiler-dependent anyway because it depends on the version of the
+    # compiler.
+    clang {
+        # Apple clang 4.0+ or clang 3.1+
+        greaterThan(QT_CLANG_MAJOR_VERSION, 3) | \
+        if(equals(QT_CLANG_MAJOR_VERSION, 3):greaterThan(QT_CLANG_MINOR_VERSION, 1)) | \
+        greaterThan(QT_APPLE_CLANG_MAJOR_VERSION, 3) {
+            QMAKE_CXXFLAGS += -Werror -Wno-error=\\$${LITERAL_HASH}warnings $$WERROR
+        }
+    } else:intel_icc {
+        # Intel CC 13.0+ (a.k.a. Intel Composer XE 2013)
+        greaterThan(QT_ICC_MAJOR_VERSION, 12) {
+            # 177: function "entity" was declared but never referenced
+            #      (too aggressive; ICC reports even for functions created due to template instantiation)
+            # 1224: #warning directive
+            # 1881: argument must be a constant null pointer value
+            #      (NULL in C++ is usually a literal 0)
+            QMAKE_CXXFLAGS += -Werror -ww177,1224,1881 $$WERROR
+        }
+    } else:gcc {
+        # GCC 4.6+
+        # note: there was no GCC 3.6 and this assumes no one is crazy enough to compile Qt with GCC 2.7
+        greaterThan(QT_GCC_MAJOR_VERSION, 4)|greaterThan(QT_GCC_MINOR_VERSION, 5) {
+            QMAKE_CXXFLAGS += -Werror -Wno-error=cpp $$WERROR
+
+            # 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
+            QMAKE_CXXFLAGS += -Wno-error=strict-overflow
+        }
+    }
+}
diff --git a/tools/configure/configureapp.cpp b/tools/configure/configureapp.cpp
index 29c1e4a661..67db7b3555 100644
--- a/tools/configure/configureapp.cpp
+++ b/tools/configure/configureapp.cpp
@@ -1,6 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
+** Copyright (C) 2013 Intel Corporation
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the tools applications of the Qt Toolkit.
@@ -244,6 +245,7 @@ Configure::Configure(int& argc, char** argv)
     dictionary[ "CFG_GCC_SYSROOT" ] = "yes";
     dictionary[ "SLOG2" ]           = "no";
     dictionary[ "SYSTEM_PROXIES" ]  = "no";
+    dictionary[ "WERROR" ]          = "auto";
 
     //Only used when cross compiling.
     dictionary[ "QT_INSTALL_SETTINGS" ] = "/etc/xdg";
@@ -891,6 +893,11 @@ void Configure::parseCmdLine()
             dictionary[ "SYSTEM_PROXIES" ] = "no";
         } else if (configCmdLine.at(i) == "-system-proxies") {
             dictionary[ "SYSTEM_PROXIES" ] = "yes";
+        } else if (configCmdLine.at(i) == "-warnings-are-errors" ||
+                   configCmdLine.at(i) == "-Werror") {
+            dictionary[ "WERROR" ] = "yes";
+        } else if (configCmdLine.at(i) == "-no-warnings-are-errors") {
+            dictionary[ "WERROR" ] = "no";
         }
 
         // Work around compiler nesting limitation
@@ -1347,8 +1354,14 @@ void Configure::parseCmdLine()
     }
 
     // Allow tests for private classes to be compiled against internal builds
-    if (dictionary["BUILDDEV"] == "yes")
-        qtConfig += "private_tests";
+    if (dictionary["BUILDDEV"] == "yes") {
+        qtConfig << "private_tests";
+        if (dictionary["WERROR"] != "no")
+            qmakeConfig << "warnings_are_errors";
+    } else {
+        if (dictionary["WERROR"] == "yes")
+            qmakeConfig << "warnings_are_errors";
+    }
 
     if (dictionary["FORCE_ASSERTS"] == "yes")
         qtConfig += "force_asserts";
@@ -1718,6 +1731,8 @@ bool Configure::displayHelp()
         desc("SYSTEM_PROXIES", "yes",  "-system-proxies",    "Use system network proxies by default.");
         desc("SYSTEM_PROXIES", "no",   "-no-system-proxies", "Do not use system network proxies by default.\n");
 
+        desc("WERROR",      "yes",     "-warnings-are-errors",   "Make warnings be treated as errors.");
+        desc("WERROR",      "no",      "-no-warnings-are-errors","Make warnings be treated normally.");
 
 #if !defined(EVAL)
         desc(                   "-qtnamespace <name>", "Wraps all Qt library code in 'namespace name {...}'.");