CMakeProjectManager: Fix clang code model when CMake PCHs are used

CMake gives the path to the cmake_pch.h[xx] file as relative path
to build directory. Making it absolute fixes the code model.

Fixes: QTCREATORBUG-22888
Change-Id: I2fdc080be779f22b737788be2074254290994aaa
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/libs/utils/fileutils.cpp

@@ -925,6 +925,12 @@ bool FilePath::isChildOf(const QDir &dir) const
     return isChildOf(FilePath::fromString(dir.absolutePath()));
 }
 
+/// \returns whether FilePath startsWith \a s
+bool FilePath::startsWith(const QString &s) const
+{
+    return m_data.startsWith(s, HostOsInfo::fileNameCaseSensitivity());
+}
+
 /// \returns whether FilePath endsWith \a s
 bool FilePath::endsWith(const QString &s) const
 {

src/libs/utils/fileutils.h

@@ -97,6 +97,7 @@ public:
 
     bool isChildOf(const FilePath &s) const;
     bool isChildOf(const QDir &dir) const;
+    bool startsWith(const QString &s) const;
     bool endsWith(const QString &s) const;
 
     bool isLocal() const;

src/plugins/cmakeprojectmanager/fileapidataextractor.cpp

@@ -271,13 +271,15 @@ static QStringList splitFragments(const QStringList &fragments)
 }
 
 RawProjectParts generateRawProjectParts(const PreprocessedData &input,
-                                        const FilePath &sourceDirectory)
+                                        const FilePath &sourceDirectory,
+                                        const FilePath &buildDirectory)
 {
     RawProjectParts rpps;
 
     int counter = 0;
     for (const TargetDetails &t : input.targetDetails) {
         QDir sourceDir(sourceDirectory.toString());
+        QDir buildDir(buildDirectory.toString());
 
         bool needPostfix = t.compileGroups.size() > 1;
         int count = 1;
@@ -321,16 +323,25 @@ RawProjectParts generateRawProjectParts(const PreprocessedData &input,
             cxxProjectFlags.commandLineFlags = cProjectFlags.commandLineFlags;
             rpp.setFlagsForCxx(cxxProjectFlags);
 
-            const QString precompiled_header
+            FilePath precompiled_header
-                = findOrDefault(t.sources, [&ending](const SourceInfo &si) {
+                = FilePath::fromString(findOrDefault(t.sources, [&ending](const SourceInfo &si) {
                                            return si.path.endsWith(ending);
-                  }).path;
+                                       }).path);
 
             rpp.setFiles(transform<QList>(ci.sources, [&t, &sourceDir](const int si) {
                 return sourceDir.absoluteFilePath(t.sources[static_cast<size_t>(si)].path);
             }));
-            if (!precompiled_header.isEmpty())
+            if (!precompiled_header.isEmpty()) {
-                rpp.setPreCompiledHeaders({precompiled_header});
+                if (precompiled_header.toFileInfo().isRelative()) {
+                    const FilePath parentDir = FilePath::fromString(buildDir.absolutePath());
+                    const QString dirName = buildDir.dirName();
+                    if (precompiled_header.startsWith(dirName))
+                        precompiled_header = FilePath::fromString(
+                            precompiled_header.toString().mid(dirName.length() + 1));
+                    precompiled_header = parentDir.pathAppended(precompiled_header.toString());
+                }
+                rpp.setPreCompiledHeaders({precompiled_header.toString()});
+            }
 
             const bool isExecutable = t.type == "EXECUTABLE";
             rpp.setBuildTargetType(isExecutable ? ProjectExplorer::BuildTargetType::Executable
@@ -602,7 +613,7 @@ FileApiQtcData extractData(FileApiData &input,
 
     result.buildTargets = generateBuildTargets(data, sourceDirectory, buildDirectory);
     result.cmakeFiles = std::move(data.cmakeFiles);
-    result.projectParts = generateRawProjectParts(data, sourceDirectory);
+    result.projectParts = generateRawProjectParts(data, sourceDirectory, buildDirectory);
 
     auto pair = generateRootProjectNode(data, sourceDirectory, buildDirectory);
     result.rootProjectNode = std::move(pair.first);