ProjectExplorer: Do not prepend compiler path to PATH everywhere!

Do not unconditionally prepend the (c++) compiler path to PATH for
all projects using GCC-derived toolchains.

Prepend the compiler path in the Qmake- and GenericBuildConfigurations
instead.

Also change the order: Apply buildconfiguration's addToEnvironment first,
only then apply the kit's addToEnvironment.

This does change a few things:
 * CMake and Qbs will now get the normal PATH
 * MSVC compilers will have their compiler path prepended to PATH
   by the effected BuildConfigurations. This should be harmless,
   since that happens before the environment setup script is appended.

Task-number: QTCREATORBUG-18714
Change-Id: I548182bc447d80d24f4de4ce7cf12ee1a753ed26
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/genericprojectmanager/genericbuildconfiguration.cpp

@@ -196,6 +196,11 @@ BuildConfiguration::BuildType GenericBuildConfiguration::buildType() const
     return Unknown;
 }
 
+void GenericBuildConfiguration::addToEnvironment(Utils::Environment &env) const
+{
+    prependCompilerPathToEnvironment(env);
+}
+
 ////////////////////////////////////////////////////////////////////////////////////
 // GenericBuildSettingsWidget
 ////////////////////////////////////////////////////////////////////////////////////

src/plugins/genericprojectmanager/genericbuildconfiguration.h

@@ -52,6 +52,8 @@ public:
 
     BuildType buildType() const override;
 
+    void addToEnvironment(Utils::Environment &env) const final;
+
 protected:
     GenericBuildConfiguration(ProjectExplorer::Target *parent, GenericBuildConfiguration *source);
     GenericBuildConfiguration(ProjectExplorer::Target *parent, Core::Id id);

src/plugins/projectexplorer/buildconfiguration.cpp

@@ -33,7 +33,10 @@
 #include "kit.h"
 
 #include <projectexplorer/buildenvironmentwidget.h>
+#include <projectexplorer/kitinformation.h>
+#include <projectexplorer/projectexplorerconstants.h>
 #include <projectexplorer/projectmacroexpander.h>
+#include <projectexplorer/target.h>
 #include <extensionsystem/pluginmanager.h>
 #include <coreplugin/idocument.h>
 
@@ -238,8 +241,8 @@ Utils::Environment BuildConfiguration::baseEnvironment() const
     Utils::Environment result;
     if (useSystemEnvironment())
         result = Utils::Environment::systemEnvironment();
-    target()->kit()->addToEnvironment(result);
     addToEnvironment(result);
+    target()->kit()->addToEnvironment(result);
     return result;
 }
 
@@ -330,6 +333,25 @@ bool BuildConfiguration::isActive() const
     return target()->isActive() && target()->activeBuildConfiguration() == this;
 }
 
+/*!
+ * Helper function that prepends the directory containing the C++ toolchain to
+ * PATH. This is used to in build configurations targeting broken build systems
+ * to provide hints about which compiler to use.
+ */
+void BuildConfiguration::prependCompilerPathToEnvironment(Utils::Environment &env) const
+{
+    const ToolChain *tc
+            = ToolChainKitInformation::toolChain(target()->kit(),
+                                                 ProjectExplorer::Constants::CXX_LANGUAGE_ID);
+
+    if (!tc)
+        return;
+
+    const Utils::FileName compilerDir = tc->compilerCommand().parentDir();
+    if (!compilerDir.isEmpty())
+        env.prependOrSetPath(compilerDir.toString());
+}
+
 ///
 // IBuildConfigurationFactory
 ///

src/plugins/projectexplorer/buildconfiguration.h

@@ -90,6 +90,8 @@ public:
 
     bool isActive() const override;
 
+    void prependCompilerPathToEnvironment(Utils::Environment &env) const;
+
 signals:
     void environmentChanged();
     void buildDirectoryChanged();

src/plugins/projectexplorer/gcctoolchain.cpp

@@ -718,7 +718,7 @@ GccToolChain::GccToolChain(const GccToolChain &) = default;
 
 void GccToolChain::addToEnvironment(Environment &env) const
 {
-    addCommandPathToEnvironment(m_compilerCommand, env);
+    Q_UNUSED(env);
 }
 
 FileNameList GccToolChain::suggestedMkspecList() const

src/plugins/qmakeprojectmanager/qmakebuildconfiguration.cpp

@@ -756,6 +756,11 @@ BuildConfiguration::BuildType QmakeBuildConfiguration::buildType() const
         return Release;
 }
 
+void QmakeBuildConfiguration::addToEnvironment(Environment &env) const
+{
+    prependCompilerPathToEnvironment(env);
+}
+
 QmakeBuildConfiguration::LastKitState::LastKitState() { }
 
 QmakeBuildConfiguration::LastKitState::LastKitState(Kit *k)

src/plugins/qmakeprojectmanager/qmakebuildconfiguration.h

@@ -99,6 +99,8 @@ public:
 
     BuildType buildType() const override;
 
+    void addToEnvironment(Utils::Environment &env) const override;
+
     void emitProFileEvaluateNeeded();
 
 signals: