CppTools: Add pre system include search path per project

Sometimes you want add a pre system include search path per project to
overload some system header for indexing. This can then even be checked in
the repository.

Change-Id: Ib103e5935d0553aa94522ed736f8c4eb2405a093
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/cpptools/headerpathfilter.cpp

@@ -29,6 +29,8 @@
 #include <coreplugin/icore.h>
 #endif
 
+#include <projectexplorer/project.h>
+
 #include <QRegularExpression>
 
 namespace CppTools {
@@ -41,6 +43,8 @@ void HeaderPathFilter::process()
 {
     const HeaderPaths &headerPaths = projectPart.headerPaths;
 
+    addPreIncludesPath();
+
     for (const HeaderPath &headerPath : headerPaths)
         filterHeaderPath(headerPath);
 
@@ -141,6 +145,18 @@ void HeaderPathFilter::tweakHeaderPaths()
     }
 }
 
+void HeaderPathFilter::addPreIncludesPath()
+{
+    if (projectDirectory.size()) {
+        Utils::FileName rootProjectDirectory = Utils::FileName::fromString(projectDirectory);
+
+        rootProjectDirectory.appendPath(".pre_includes");
+
+        systemHeaderPaths.push_back(
+            {rootProjectDirectory.toString(), ProjectExplorer::HeaderPathType::System});
+    }
+}
+
 QString HeaderPathFilter::ensurePathWithSlashEnding(const QString &path)
 {
     QString pathWithSlashEnding = path;

src/plugins/cpptools/headerpathfilter.h

@@ -53,6 +53,8 @@ private:
 
     void tweakHeaderPaths();
 
+    void addPreIncludesPath();
+
     bool isProjectHeaderPath(const QString &path) const;
 
     static QString ensurePathWithSlashEnding(const QString &path);