MSVC: Consider build environment when calculating header paths

Fixes: QTCREATORBUG-25816
Change-Id: Id6274d2bec4ed3db07729f1d88a5a9ad82c8d98d
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/projectexplorer/msvctoolchain.cpp

@@ -1125,13 +1125,15 @@ ToolChain::BuiltInHeaderPathsRunner MsvcToolChain::createBuiltInHeaderPathsRunne
 
     return [this, fullEnv](const QStringList &, const QString &, const QString &) {
         QMutexLocker locker(&m_headerPathsMutex);
-        if (m_headerPaths.isEmpty()) {
+        const auto envList = fullEnv.toStringList();
-            m_headerPaths = transform<QVector>(fullEnv.pathListValue("INCLUDE"),
+        const auto it = m_headerPathsPerEnv.constFind(envList);
-                                               [](const FilePath &p) {
+        if (it != m_headerPathsPerEnv.cend())
-                return HeaderPath(p.toString(), HeaderPathType::BuiltIn);
+            return *it;
-            });
+        const auto mapper = [](const FilePath &p) { // TODO: Define functions for this.
-        }
+            return HeaderPath(p.toString(), HeaderPathType::BuiltIn);
-        return m_headerPaths;
+        };
+        return *m_headerPathsPerEnv.insert(envList,
+                    transform<QVector>(fullEnv.pathListValue("INCLUDE"), mapper));
     };
 }
 
@@ -1787,7 +1789,7 @@ ClangClToolChain::BuiltInHeaderPathsRunner ClangClToolChain::createBuiltInHeader
 {
     {
         QMutexLocker locker(&m_headerPathsMutex);
-        m_headerPaths.clear();
+        m_headerPathsPerEnv.clear();
     }
 
     return MsvcToolChain::createBuiltInHeaderPathsRunner(env);

src/plugins/projectexplorer/msvctoolchain.h

@@ -140,7 +140,7 @@ protected:
 
 protected:
     mutable QMutex m_headerPathsMutex;
-    mutable HeaderPaths m_headerPaths;
+    mutable QHash<QStringList, HeaderPaths> m_headerPathsPerEnv;
 
 private:
     void updateEnvironmentModifications(Utils::EnvironmentItems modifications);