CppEditor: Move CppHeaderSource implementation and test to same files

... and remove the now-empty cppeditorplugin.h

Change-Id: Ia28b180c280ba7b10ce0f2826f2ac69d128a453c
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

19 files changed, 384 insertions, 388 deletions

diff --git a/src/plugins/cppeditor/CMakeLists.txt b/src/plugins/cppeditor/CMakeLists.txt
index c64817cfb0..ec5ad89cea 100644
--- a/src/plugins/cppeditor/CMakeLists.txt
+++ b/src/plugins/cppeditor/CMakeLists.txt
@@ -40,7 +40,7 @@ add_qtc_plugin(CppEditor
     cppeditorconstants.h
     cppeditordocument.cpp cppeditordocument.h
     cppeditoroutline.cpp cppeditoroutline.h
-    cppeditorplugin.cpp cppeditorplugin.h
+    cppeditorplugin.cpp
     cppeditorwidget.cpp cppeditorwidget.h
     cppelementevaluator.cpp cppelementevaluator.h
     cppfileiterationorder.cpp cppfileiterationorder.h
@@ -49,6 +49,7 @@ add_qtc_plugin(CppEditor
     cppfollowsymbolundercursor.cpp cppfollowsymbolundercursor.h
     cppfunctiondecldeflink.cpp cppfunctiondecldeflink.h
     cppfunctionparamrenaminghandler.cpp cppfunctionparamrenaminghandler.h
+    cppheadersource.cpp cppheadersource.h
     cpphighlighter.cpp cpphighlighter.h
     cppincludehierarchy.cpp cppincludehierarchy.h
     cppincludesfilter.cpp cppincludesfilter.h
@@ -121,7 +122,6 @@ extend_qtc_plugin(CppEditor
     cppcodegen_test.cpp cppcodegen_test.h
     cppcompletion_test.cpp cppcompletion_test.h
     cppdoxygen_test.cpp cppdoxygen_test.h
-    cppheadersource_test.cpp cppheadersource_test.h
     cppincludehierarchy_test.cpp cppincludehierarchy_test.h
     cpplocalsymbols_test.cpp cpplocalsymbols_test.h
     cpplocatorfilter_test.cpp cpplocatorfilter_test.h
diff --git a/src/plugins/cppeditor/builtineditordocumentprocessor.cpp b/src/plugins/cppeditor/builtineditordocumentprocessor.cpp
index 9c7535ee74..4d43546334 100644
--- a/src/plugins/cppeditor/builtineditordocumentprocessor.cpp
+++ b/src/plugins/cppeditor/builtineditordocumentprocessor.cpp
@@ -7,7 +7,6 @@
 #include "cppchecksymbols.h"
 #include "cppcodemodelsettings.h"
 #include "cppeditordocument.h"
-#include "cppeditorplugin.h"
 #include "cppmodelmanager.h"
 #include "cpptoolsreuse.h"
 #include "cppworkingcopy.h"
diff --git a/src/plugins/cppeditor/cppautocompleter.cpp b/src/plugins/cppeditor/cppautocompleter.cpp
index dcd2cebacd..0710131862 100644
--- a/src/plugins/cppeditor/cppautocompleter.cpp
+++ b/src/plugins/cppeditor/cppautocompleter.cpp
@@ -13,7 +13,6 @@
 
 #ifdef WITH_TESTS
 #include "cppeditorconstants.h"
-#include "cppeditorplugin.h"
 #include "cppeditorwidget.h"
 
 #include <coreplugin/editormanager/editormanager.h>
diff --git a/src/plugins/cppeditor/cppeditor.qbs b/src/plugins/cppeditor/cppeditor.qbs
index 2e8581a50c..b684b0e0ea 100644
--- a/src/plugins/cppeditor/cppeditor.qbs
+++ b/src/plugins/cppeditor/cppeditor.qbs
@@ -95,7 +95,6 @@ QtcPlugin {
         "cppeditoroutline.cpp",
         "cppeditoroutline.h",
         "cppeditorplugin.cpp",
-        "cppeditorplugin.h",
         "cppelementevaluator.cpp",
         "cppelementevaluator.h",
         "cppfileiterationorder.cpp",
@@ -110,6 +109,8 @@ QtcPlugin {
         "cppfunctiondecldeflink.h",
         "cppfunctionparamrenaminghandler.cpp",
         "cppfunctionparamrenaminghandler.h",
+        "cppheadersource.cpp",
+        "cppheadersource.h",
         "cpphighlighter.cpp",
         "cpphighlighter.h",
         "cppincludehierarchy.cpp",
@@ -252,8 +253,6 @@ QtcPlugin {
             "cppcompletion_test.h",
             "cppdoxygen_test.cpp",
             "cppdoxygen_test.h",
-            "cppheadersource_test.cpp",
-            "cppheadersource_test.h",
             "cppincludehierarchy_test.cpp",
             "cppincludehierarchy_test.h",
             "cpplocalsymbols_test.cpp",
diff --git a/src/plugins/cppeditor/cppeditordocument.cpp b/src/plugins/cppeditor/cppeditordocument.cpp
index 8d4adebf14..d1297b1dd3 100644
--- a/src/plugins/cppeditor/cppeditordocument.cpp
+++ b/src/plugins/cppeditor/cppeditordocument.cpp
@@ -6,11 +6,9 @@
 #include "baseeditordocumentparser.h"
 #include "cppcodeformatter.h"
 #include "cppeditorconstants.h"
-#include "cppeditorplugin.h"
 #include "cppeditortr.h"
 #include "cppmodelmanager.h"
 #include "cppeditorconstants.h"
-#include "cppeditorplugin.h"
 #include "cppeditortr.h"
 #include "cpphighlighter.h"
 #include "cppquickfixassistant.h"
diff --git a/src/plugins/cppeditor/cppeditorplugin.cpp b/src/plugins/cppeditor/cppeditorplugin.cpp
index 24d821aac2..a5f1275538 100644
--- a/src/plugins/cppeditor/cppeditorplugin.cpp
+++ b/src/plugins/cppeditor/cppeditorplugin.cpp
@@ -1,8 +1,6 @@
 // Copyright (C) 2016 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
 
-#include "cppeditorplugin.h"
-
 #include "cppautocompleter.h"
 #include "cppcodemodelinspectordialog.h"
 #include "cppcodemodelsettings.h"
@@ -14,9 +12,9 @@
 #include "cppeditorwidget.h"
 #include "cppfilesettingspage.h"
 #include "cppincludehierarchy.h"
+#include "cppheadersource.h"
 #include "cppmodelmanager.h"
 #include "cppoutline.h"
-#include "cppprojectfile.h"
 #include "cppprojectupdater.h"
 #include "cppquickfixes.h"
 #include "cppquickfixprojectsettingswidget.h"
@@ -24,7 +22,6 @@
 #include "cpptoolsreuse.h"
 #include "cpptoolssettings.h"
 #include "cpptypehierarchy.h"
-#include "projectinfo.h"
 #include "resourcepreviewhoverhandler.h"
 
 #ifdef WITH_TESTS
@@ -32,7 +29,6 @@
 #include "cppcodegen_test.h"
 #include "cppcompletion_test.h"
 #include "cppdoxygen_test.h"
-#include "cppheadersource_test.h"
 #include "cpphighlighter.h"
 #include "cppincludehierarchy_test.h"
 #include "cppinsertvirtualmethods.h"
@@ -89,7 +85,6 @@
 #include <utils/mimeconstants.h>
 #include <utils/mimeutils.h>
 #include <utils/qtcassert.h>
-#include <utils/stringtable.h>
 #include <utils/theme/theme.h>
 
 #include <QAction>
@@ -106,11 +101,7 @@ using namespace ProjectExplorer;
 using namespace TextEditor;
 using namespace Utils;
 
-namespace CppEditor {
-namespace Internal {
-
-enum { QUICKFIX_INTERVAL = 20 };
-enum { debug = 0 };
+namespace CppEditor::Internal {
 
 static CppEditorWidget *currentCppEditorWidget()
 {
@@ -183,8 +174,6 @@ public:
     CppProjectUpdaterFactory m_cppProjectUpdaterFactory;
 };
 
-static QHash<FilePath, FilePath> m_headerSourceMapping;
-
 class CppEditorPlugin final : public ExtensionSystem::IPlugin
 {
     Q_OBJECT
@@ -498,7 +487,7 @@ void CppEditorPlugin::registerTests()
     addTest<CppHighlighterTest>();
     addTest<FunctionUtilsTest>();
     addTest<HeaderPathFilterTest>();
-    addTest<HeaderSourceTest>();
+    addTestCreator(createCppHeaderSourceTest);
     addTest<IncludeGroupsTest>();
     addTest<LocalSymbolsTest>();
     addTest<LocatorFilterTest>();
@@ -551,239 +540,6 @@ void CppEditorPluginPrivate::inspectCppCodeModel()
     }
 }
 
-void clearHeaderSourceCache()
-{
-    m_headerSourceMapping.clear();
-}
-
-static FilePaths findFilesInProject(const QStringList &names, const Project *project,
-                                      FileType fileType)
-{
-    if (debug)
-        qDebug() << Q_FUNC_INFO << names << project;
-
-    if (!project)
-        return {};
-
-    const auto filter = [&](const Node *n) {
-        const auto fn = n->asFileNode();
-        return fn && fn->fileType() == fileType && names.contains(fn->filePath().fileName());
-    };
-    return project->files(filter);
-}
-
-// Return the suffixes that should be checked when trying to find a
-// source belonging to a header and vice versa
-static QStringList matchingCandidateSuffixes(ProjectFile::Kind kind)
-{
-    using namespace Utils::Constants;
-    switch (kind) {
-    case ProjectFile::AmbiguousHeader:
-    case ProjectFile::CHeader:
-    case ProjectFile::CXXHeader:
-    case ProjectFile::ObjCHeader:
-    case ProjectFile::ObjCXXHeader:
-        return mimeTypeForName(C_SOURCE_MIMETYPE).suffixes()
-             + mimeTypeForName(CPP_SOURCE_MIMETYPE).suffixes()
-             + mimeTypeForName(OBJECTIVE_C_SOURCE_MIMETYPE).suffixes()
-             + mimeTypeForName(OBJECTIVE_CPP_SOURCE_MIMETYPE).suffixes()
-             + mimeTypeForName(CUDA_SOURCE_MIMETYPE).suffixes();
-    case ProjectFile::CSource:
-    case ProjectFile::ObjCSource:
-        return mimeTypeForName(C_HEADER_MIMETYPE).suffixes();
-    case ProjectFile::CXXSource:
-    case ProjectFile::ObjCXXSource:
-    case ProjectFile::CudaSource:
-    case ProjectFile::OpenCLSource:
-        return mimeTypeForName(CPP_HEADER_MIMETYPE).suffixes();
-    default:
-        return {};
-    }
-}
-
-static QStringList baseNameWithAllSuffixes(const QString &baseName, const QStringList &suffixes)
-{
-    QStringList result;
-    const QChar dot = QLatin1Char('.');
-    for (const QString &suffix : suffixes) {
-        QString fileName = baseName;
-        fileName += dot;
-        fileName += suffix;
-        result += fileName;
-    }
-    return result;
-}
-
-static QStringList baseNamesWithAllPrefixes(const CppFileSettings &settings,
-                                            const QStringList &baseNames, bool isHeader)
-{
-    QStringList result;
-    const QStringList &sourcePrefixes = settings.sourcePrefixes;
-    const QStringList &headerPrefixes = settings.headerPrefixes;
-
-    for (const QString &name : baseNames) {
-        for (const QString &prefix : isHeader ? headerPrefixes : sourcePrefixes) {
-            if (name.startsWith(prefix)) {
-                QString nameWithoutPrefix = name.mid(prefix.size());
-                result += nameWithoutPrefix;
-                for (const QString &prefix : isHeader ? sourcePrefixes : headerPrefixes)
-                    result += prefix + nameWithoutPrefix;
-            }
-        }
-        for (const QString &prefix : isHeader ? sourcePrefixes : headerPrefixes)
-            result += prefix + name;
-
-    }
-    return result;
-}
-
-static QStringList baseDirWithAllDirectories(const QDir &baseDir, const QStringList &directories)
-{
-    QStringList result;
-    for (const QString &dir : directories)
-        result << QDir::cleanPath(baseDir.absoluteFilePath(dir));
-    return result;
-}
-
-static int commonFilePathLength(const QString &s1, const QString &s2)
-{
-    int length = qMin(s1.length(), s2.length());
-    for (int i = 0; i < length; ++i)
-        if (HostOsInfo::fileNameCaseSensitivity() == Qt::CaseSensitive) {
-            if (s1[i] != s2[i])
-                return i;
-        } else {
-            if (s1[i].toLower() != s2[i].toLower())
-                return i;
-        }
-    return length;
-}
-
-static FilePath correspondingHeaderOrSourceInProject(const FilePath &filePath,
-                                                     const QStringList &candidateFileNames,
-                                                     const Project *project,
-                                                     FileType fileType,
-                                                     CacheUsage cacheUsage)
-{
-    const FilePaths projectFiles = findFilesInProject(candidateFileNames, project, fileType);
-
-    // Find the file having the most common path with fileName
-    FilePath bestFilePath;
-    int compareValue = 0;
-    for (const FilePath &projectFile : projectFiles) {
-        int value = commonFilePathLength(filePath.toString(), projectFile.toString());
-        if (value > compareValue) {
-            compareValue = value;
-            bestFilePath = projectFile;
-        }
-    }
-    if (!bestFilePath.isEmpty()) {
-        QTC_ASSERT(bestFilePath.isFile(), return {});
-        if (cacheUsage == CacheUsage::ReadWrite) {
-            m_headerSourceMapping[filePath] = bestFilePath;
-            m_headerSourceMapping[bestFilePath] = filePath;
-        }
-        return bestFilePath;
-    }
-
-    return {};
-}
-
-} // namespace Internal
-
-using namespace Internal;
-
-FilePath correspondingHeaderOrSource(const FilePath &filePath, bool *wasHeader, CacheUsage cacheUsage)
-{
-    ProjectFile::Kind kind = ProjectFile::classify(filePath.fileName());
-    const bool isHeader = ProjectFile::isHeader(kind);
-    if (wasHeader)
-        *wasHeader = isHeader;
-    if (const auto it = m_headerSourceMapping.constFind(filePath);
-        it != m_headerSourceMapping.constEnd()) {
-        return it.value();
-    }
-
-    Project * const projectForFile = ProjectManager::projectForFile(filePath);
-    const CppFileSettings settings = cppFileSettingsForProject(projectForFile);
-
-    if (debug)
-        qDebug() << Q_FUNC_INFO << filePath.fileName() <<  kind;
-
-    if (kind == ProjectFile::Unsupported)
-        return {};
-
-    const QString baseName = filePath.completeBaseName();
-    const QString privateHeaderSuffix = QLatin1String("_p");
-    const QStringList suffixes = matchingCandidateSuffixes(kind);
-
-    QStringList candidateFileNames = baseNameWithAllSuffixes(baseName, suffixes);
-    if (isHeader) {
-        if (baseName.endsWith(privateHeaderSuffix)) {
-            QString sourceBaseName = baseName;
-            sourceBaseName.truncate(sourceBaseName.size() - privateHeaderSuffix.size());
-            candidateFileNames += baseNameWithAllSuffixes(sourceBaseName, suffixes);
-        }
-    } else {
-        QString privateHeaderBaseName = baseName;
-        privateHeaderBaseName.append(privateHeaderSuffix);
-        candidateFileNames += baseNameWithAllSuffixes(privateHeaderBaseName, suffixes);
-    }
-
-    const QDir absoluteDir = filePath.toFileInfo().absoluteDir();
-    QStringList candidateDirs(absoluteDir.absolutePath());
-    // If directory is not root, try matching against its siblings
-    const QStringList searchPaths = isHeader ? settings.sourceSearchPaths
-                                             : settings.headerSearchPaths;
-    candidateDirs += baseDirWithAllDirectories(absoluteDir, searchPaths);
-
-    candidateFileNames += baseNamesWithAllPrefixes(settings, candidateFileNames, isHeader);
-
-    // Try to find a file in the same or sibling directories first
-    for (const QString &candidateDir : std::as_const(candidateDirs)) {
-        for (const QString &candidateFileName : std::as_const(candidateFileNames)) {
-            const FilePath candidateFilePath
-                = FilePath::fromString(candidateDir + '/' + candidateFileName).normalizedPathName();
-            if (candidateFilePath.isFile()) {
-                if (cacheUsage == CacheUsage::ReadWrite) {
-                    m_headerSourceMapping[filePath] = candidateFilePath;
-                    if (!isHeader || !baseName.endsWith(privateHeaderSuffix))
-                        m_headerSourceMapping[candidateFilePath] = filePath;
-                }
-                return candidateFilePath;
-            }
-        }
-    }
-
-    // Find files in the current project
-    Project *currentProject = projectForFile;
-    if (!projectForFile)
-        currentProject = ProjectTree::currentProject();
-    const FileType requestedFileType = isHeader ? FileType::Source : FileType::Header;
-    if (currentProject) {
-        const FilePath path = correspondingHeaderOrSourceInProject(
-            filePath, candidateFileNames, currentProject, requestedFileType, cacheUsage);
-        if (!path.isEmpty())
-            return path;
-
-    // Find files in other projects
-    } else {
-        const QList<ProjectInfo::ConstPtr> projectInfos = CppModelManager::projectInfos();
-        for (const ProjectInfo::ConstPtr &projectInfo : projectInfos) {
-            const Project *project = projectForProjectInfo(*projectInfo);
-            if (project == currentProject)
-                continue; // We have already checked the current project.
-
-            const FilePath path = correspondingHeaderOrSourceInProject(
-                filePath, candidateFileNames, project, requestedFileType, cacheUsage);
-            if (!path.isEmpty())
-                return path;
-        }
-    }
-
-    return {};
-}
-
-} // namespace CppEditor
+} // CppEditor::Internal
 
 #include "cppeditorplugin.moc"
diff --git a/src/plugins/cppeditor/cppeditorwidget.cpp b/src/plugins/cppeditor/cppeditorwidget.cpp
index 2d8a699727..958a908915 100644
--- a/src/plugins/cppeditor/cppeditorwidget.cpp
+++ b/src/plugins/cppeditor/cppeditorwidget.cpp
@@ -8,7 +8,6 @@
 #include "cppeditorconstants.h"
 #include "cppeditordocument.h"
 #include "cppeditoroutline.h"
-#include "cppeditorplugin.h"
 #include "cppeditortr.h"
 #include "cppfunctiondecldeflink.h"
 #include "cppfunctionparamrenaminghandler.h"
diff --git a/src/plugins/cppeditor/cppfilesettingspage.cpp b/src/plugins/cppeditor/cppfilesettingspage.cpp
index d11a811498..2c8fa41054 100644
--- a/src/plugins/cppeditor/cppfilesettingspage.cpp
+++ b/src/plugins/cppeditor/cppfilesettingspage.cpp
@@ -3,8 +3,8 @@
 
 #include "cppfilesettingspage.h"
 
-#include "cppeditorplugin.h"
 #include "cppeditortr.h"
+#include "cppheadersource.h"
 
 #include <coreplugin/icore.h>
 #include <coreplugin/editormanager/editormanager.h>
diff --git a/src/plugins/cppeditor/cppheadersource.cpp b/src/plugins/cppeditor/cppheadersource.cpp
new file mode 100644
index 0000000000..84dcb98c70
--- /dev/null
+++ b/src/plugins/cppeditor/cppheadersource.cpp
@@ -0,0 +1,368 @@
+// Copyright (C) 2016 Orgad Shaneh <orgads@gmail.com>.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#include "cppheadersource.h"
+
+#include "cpptoolsreuse.h"
+#include "cpptoolstestcase.h"
+#include "cppfilesettingspage.h"
+#include "cppmodelmanager.h"
+#include "cppfilesettingspage.h"
+
+#include <projectexplorer/project.h>
+#include <projectexplorer/projectnodes.h>
+#include <projectexplorer/projectmanager.h>
+#include <projectexplorer/projecttree.h>
+
+#include <utils/fileutils.h>
+#include <utils/mimeconstants.h>
+#include <utils/mimeutils.h>
+#include <utils/temporarydirectory.h>
+
+#include <QDir>
+
+#ifdef WITH_TESTS
+#include <QtTest>
+#endif
+
+using namespace CppEditor::Internal;
+using namespace ProjectExplorer;
+using namespace Utils;
+
+namespace CppEditor {
+
+enum { debug = 0 };
+
+static QHash<FilePath, FilePath> m_headerSourceMapping;
+
+void Internal::clearHeaderSourceCache()
+{
+    m_headerSourceMapping.clear();
+}
+
+static inline QString _(const QByteArray &ba) { return QString::fromLatin1(ba, ba.size()); }
+
+static void createTempFile(const FilePath &filePath)
+{
+    QString fileName = filePath.toString();
+    QFile file(fileName);
+    QDir(QFileInfo(fileName).absolutePath()).mkpath(_("."));
+    file.open(QFile::WriteOnly);
+    file.close();
+}
+
+static QString baseTestDir()
+{
+    return Utils::TemporaryDirectory::masterDirectoryPath() + "/qtc_cppheadersource/";
+}
+
+static FilePaths findFilesInProject(const QStringList &names, const Project *project,
+                                    FileType fileType)
+{
+    if (debug)
+        qDebug() << Q_FUNC_INFO << names << project;
+
+    if (!project)
+        return {};
+
+    const auto filter = [&](const Node *n) {
+        const auto fn = n->asFileNode();
+        return fn && fn->fileType() == fileType && names.contains(fn->filePath().fileName());
+    };
+    return project->files(filter);
+}
+
+// Return the suffixes that should be checked when trying to find a
+// source belonging to a header and vice versa
+static QStringList matchingCandidateSuffixes(ProjectFile::Kind kind)
+{
+    using namespace Utils::Constants;
+    switch (kind) {
+    case ProjectFile::AmbiguousHeader:
+    case ProjectFile::CHeader:
+    case ProjectFile::CXXHeader:
+    case ProjectFile::ObjCHeader:
+    case ProjectFile::ObjCXXHeader:
+        return mimeTypeForName(C_SOURCE_MIMETYPE).suffixes()
+             + mimeTypeForName(CPP_SOURCE_MIMETYPE).suffixes()
+             + mimeTypeForName(OBJECTIVE_C_SOURCE_MIMETYPE).suffixes()
+             + mimeTypeForName(OBJECTIVE_CPP_SOURCE_MIMETYPE).suffixes()
+             + mimeTypeForName(CUDA_SOURCE_MIMETYPE).suffixes();
+    case ProjectFile::CSource:
+    case ProjectFile::ObjCSource:
+        return mimeTypeForName(C_HEADER_MIMETYPE).suffixes();
+    case ProjectFile::CXXSource:
+    case ProjectFile::ObjCXXSource:
+    case ProjectFile::CudaSource:
+    case ProjectFile::OpenCLSource:
+        return mimeTypeForName(CPP_HEADER_MIMETYPE).suffixes();
+    default:
+        return {};
+    }
+}
+
+static QStringList baseNameWithAllSuffixes(const QString &baseName, const QStringList &suffixes)
+{
+    QStringList result;
+    const QChar dot = QLatin1Char('.');
+    for (const QString &suffix : suffixes) {
+        QString fileName = baseName;
+        fileName += dot;
+        fileName += suffix;
+        result += fileName;
+    }
+    return result;
+}
+
+static QStringList baseNamesWithAllPrefixes(const CppFileSettings &settings,
+                                            const QStringList &baseNames, bool isHeader)
+{
+    QStringList result;
+    const QStringList &sourcePrefixes = settings.sourcePrefixes;
+    const QStringList &headerPrefixes = settings.headerPrefixes;
+
+    for (const QString &name : baseNames) {
+        for (const QString &prefix : isHeader ? headerPrefixes : sourcePrefixes) {
+            if (name.startsWith(prefix)) {
+                QString nameWithoutPrefix = name.mid(prefix.size());
+                result += nameWithoutPrefix;
+                for (const QString &prefix : isHeader ? sourcePrefixes : headerPrefixes)
+                    result += prefix + nameWithoutPrefix;
+            }
+        }
+        for (const QString &prefix : isHeader ? sourcePrefixes : headerPrefixes)
+            result += prefix + name;
+
+    }
+    return result;
+}
+
+static QStringList baseDirWithAllDirectories(const QDir &baseDir, const QStringList &directories)
+{
+    QStringList result;
+    for (const QString &dir : directories)
+        result << QDir::cleanPath(baseDir.absoluteFilePath(dir));
+    return result;
+}
+
+static int commonFilePathLength(const QString &s1, const QString &s2)
+{
+    int length = qMin(s1.length(), s2.length());
+    for (int i = 0; i < length; ++i)
+        if (HostOsInfo::fileNameCaseSensitivity() == Qt::CaseSensitive) {
+            if (s1[i] != s2[i])
+                return i;
+        } else {
+            if (s1[i].toLower() != s2[i].toLower())
+                return i;
+        }
+    return length;
+}
+
+static FilePath correspondingHeaderOrSourceInProject(const FilePath &filePath,
+                                                     const QStringList &candidateFileNames,
+                                                     const Project *project,
+                                                     FileType fileType,
+                                                     CacheUsage cacheUsage)
+{
+    const FilePaths projectFiles = findFilesInProject(candidateFileNames, project, fileType);
+
+    // Find the file having the most common path with fileName
+    FilePath bestFilePath;
+    int compareValue = 0;
+    for (const FilePath &projectFile : projectFiles) {
+        int value = commonFilePathLength(filePath.toString(), projectFile.toString());
+        if (value > compareValue) {
+            compareValue = value;
+            bestFilePath = projectFile;
+        }
+    }
+    if (!bestFilePath.isEmpty()) {
+        QTC_ASSERT(bestFilePath.isFile(), return {});
+        if (cacheUsage == CacheUsage::ReadWrite) {
+            m_headerSourceMapping[filePath] = bestFilePath;
+            m_headerSourceMapping[bestFilePath] = filePath;
+        }
+        return bestFilePath;
+    }
+
+    return {};
+}
+
+FilePath correspondingHeaderOrSource(const FilePath &filePath, bool *wasHeader, CacheUsage cacheUsage)
+{
+    ProjectFile::Kind kind = ProjectFile::classify(filePath.fileName());
+    const bool isHeader = ProjectFile::isHeader(kind);
+    if (wasHeader)
+        *wasHeader = isHeader;
+    if (const auto it = m_headerSourceMapping.constFind(filePath);
+        it != m_headerSourceMapping.constEnd()) {
+        return it.value();
+    }
+
+    Project * const projectForFile = ProjectManager::projectForFile(filePath);
+    const CppFileSettings settings = cppFileSettingsForProject(projectForFile);
+
+    if (debug)
+        qDebug() << Q_FUNC_INFO << filePath.fileName() <<  kind;
+
+    if (kind == ProjectFile::Unsupported)
+        return {};
+
+    const QString baseName = filePath.completeBaseName();
+    const QString privateHeaderSuffix = QLatin1String("_p");
+    const QStringList suffixes = matchingCandidateSuffixes(kind);
+
+    QStringList candidateFileNames = baseNameWithAllSuffixes(baseName, suffixes);
+    if (isHeader) {
+        if (baseName.endsWith(privateHeaderSuffix)) {
+            QString sourceBaseName = baseName;
+            sourceBaseName.truncate(sourceBaseName.size() - privateHeaderSuffix.size());
+            candidateFileNames += baseNameWithAllSuffixes(sourceBaseName, suffixes);
+        }
+    } else {
+        QString privateHeaderBaseName = baseName;
+        privateHeaderBaseName.append(privateHeaderSuffix);
+        candidateFileNames += baseNameWithAllSuffixes(privateHeaderBaseName, suffixes);
+    }
+
+    const QDir absoluteDir = filePath.toFileInfo().absoluteDir();
+    QStringList candidateDirs(absoluteDir.absolutePath());
+    // If directory is not root, try matching against its siblings
+    const QStringList searchPaths = isHeader ? settings.sourceSearchPaths
+                                             : settings.headerSearchPaths;
+    candidateDirs += baseDirWithAllDirectories(absoluteDir, searchPaths);
+
+    candidateFileNames += baseNamesWithAllPrefixes(settings, candidateFileNames, isHeader);
+
+    // Try to find a file in the same or sibling directories first
+    for (const QString &candidateDir : std::as_const(candidateDirs)) {
+        for (const QString &candidateFileName : std::as_const(candidateFileNames)) {
+            const FilePath candidateFilePath
+                = FilePath::fromString(candidateDir + '/' + candidateFileName).normalizedPathName();
+            if (candidateFilePath.isFile()) {
+                if (cacheUsage == CacheUsage::ReadWrite) {
+                    m_headerSourceMapping[filePath] = candidateFilePath;
+                    if (!isHeader || !baseName.endsWith(privateHeaderSuffix))
+                        m_headerSourceMapping[candidateFilePath] = filePath;
+                }
+                return candidateFilePath;
+            }
+        }
+    }
+
+    // Find files in the current project
+    Project *currentProject = projectForFile;
+    if (!projectForFile)
+        currentProject = ProjectTree::currentProject();
+    const FileType requestedFileType = isHeader ? FileType::Source : FileType::Header;
+    if (currentProject) {
+        const FilePath path = correspondingHeaderOrSourceInProject(
+            filePath, candidateFileNames, currentProject, requestedFileType, cacheUsage);
+        if (!path.isEmpty())
+            return path;
+
+    // Find files in other projects
+    } else {
+        const QList<ProjectInfo::ConstPtr> projectInfos = CppModelManager::projectInfos();
+        for (const ProjectInfo::ConstPtr &projectInfo : projectInfos) {
+            const Project *project = projectForProjectInfo(*projectInfo);
+            if (project == currentProject)
+                continue; // We have already checked the current project.
+
+            const FilePath path = correspondingHeaderOrSourceInProject(
+                filePath, candidateFileNames, project, requestedFileType, cacheUsage);
+            if (!path.isEmpty())
+                return path;
+        }
+    }
+
+    return {};
+}
+
+} // CppEditor
+
+#ifdef WITH_TESTS
+
+namespace CppEditor::Internal {
+
+class HeaderSourceTest : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void initTestCase();
+    void cleanupTestCase();
+
+    void test_data();
+    void test();
+};
+
+void HeaderSourceTest::test()
+{
+    QFETCH(QString, sourceFileName);
+    QFETCH(QString, headerFileName);
+
+    CppEditor::Tests::TemporaryDir temporaryDir;
+    QVERIFY(temporaryDir.isValid());
+
+    const QDir path = QDir(temporaryDir.path() + QLatin1Char('/') + _(QTest::currentDataTag()));
+    const FilePath sourcePath = FilePath::fromString(path.absoluteFilePath(sourceFileName));
+    const FilePath headerPath = FilePath::fromString(path.absoluteFilePath(headerFileName));
+    createTempFile(sourcePath);
+    createTempFile(headerPath);
+
+    bool wasHeader;
+    clearHeaderSourceCache();
+    QCOMPARE(correspondingHeaderOrSource(sourcePath, &wasHeader, CacheUsage::ReadWrite), headerPath);
+    QVERIFY(!wasHeader);
+    clearHeaderSourceCache();
+    QCOMPARE(correspondingHeaderOrSource(headerPath, &wasHeader, CacheUsage::ReadWrite), sourcePath);
+    QVERIFY(wasHeader);
+}
+
+void HeaderSourceTest::test_data()
+{
+    QTest::addColumn<QString>("sourceFileName");
+    QTest::addColumn<QString>("headerFileName");
+    QTest::newRow("samedir") << _("foo.cpp") << _("foo.h");
+    QTest::newRow("includesub") << _("foo.cpp") << _("include/foo.h");
+    QTest::newRow("headerprefix") << _("foo.cpp") << _("testh_foo.h");
+    QTest::newRow("sourceprefixwsub") << _("testc_foo.cpp") << _("include/foo.h");
+    QTest::newRow("sourceAndHeaderPrefixWithBothsub") << _("src/testc_foo.cpp") << _("include/testh_foo.h");
+}
+
+void HeaderSourceTest::initTestCase()
+{
+    QDir(baseTestDir()).mkpath(_("."));
+    CppFileSettings &fs = globalCppFileSettings();
+    fs.headerSearchPaths.append(QLatin1String("include"));
+    fs.headerSearchPaths.append(QLatin1String("../include"));
+    fs.sourceSearchPaths.append(QLatin1String("src"));
+    fs.sourceSearchPaths.append(QLatin1String("../src"));
+    fs.headerPrefixes.append(QLatin1String("testh_"));
+    fs.sourcePrefixes.append(QLatin1String("testc_"));
+}
+
+void HeaderSourceTest::cleanupTestCase()
+{
+    Utils::FilePath::fromString(baseTestDir()).removeRecursively();
+    CppFileSettings &fs = globalCppFileSettings();
+    fs.headerSearchPaths.removeLast();
+    fs.headerSearchPaths.removeLast();
+    fs.sourceSearchPaths.removeLast();
+    fs.sourceSearchPaths.removeLast();
+    fs.headerPrefixes.removeLast();
+    fs.sourcePrefixes.removeLast();
+}
+
+QObject *createCppHeaderSourceTest()
+{
+    return new HeaderSourceTest;
+}
+
+} // namespace CppEditor::Internal
+
+#include "cppheadersource.moc"
+
+#endif // WITH_TESTS
diff --git a/src/plugins/cppeditor/cppeditorplugin.h b/src/plugins/cppeditor/cppheadersource.h
index 8dde52b15e..a408e4aac3 100644
--- a/src/plugins/cppeditor/cppeditorplugin.h
+++ b/src/plugins/cppeditor/cppheadersource.h
@@ -1,10 +1,16 @@
-// Copyright (C) 2016 The Qt Company Ltd.
+// Copyright (C) 2021 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
 
 #pragma once
 
+#include <QObject>
+
 namespace CppEditor::Internal {
 
 void clearHeaderSourceCache();
 
+#ifdef WITH_TESTS
+QObject *createCppHeaderSourceTest();
+#endif
+
 } // CppEditor::Internal
diff --git a/src/plugins/cppeditor/cppheadersource_test.cpp b/src/plugins/cppeditor/cppheadersource_test.cpp
deleted file mode 100644
index 2b6621c74f..0000000000
--- a/src/plugins/cppeditor/cppheadersource_test.cpp
+++ /dev/null
@@ -1,95 +0,0 @@
-// Copyright (C) 2016 Orgad Shaneh <orgads@gmail.com>.
-// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
-
-#include "cppheadersource_test.h"
-
-#include "cppeditorplugin.h"
-#include "cpptoolsreuse.h"
-#include "cpptoolstestcase.h"
-#include "cppfilesettingspage.h"
-
-#include <utils/fileutils.h>
-#include <utils/temporarydirectory.h>
-
-#include <QDir>
-#include <QtTest>
-
-using namespace Utils;
-
-static inline QString _(const QByteArray &ba) { return QString::fromLatin1(ba, ba.size()); }
-
-static void createTempFile(const FilePath &filePath)
-{
-    QString fileName = filePath.toString();
-    QFile file(fileName);
-    QDir(QFileInfo(fileName).absolutePath()).mkpath(_("."));
-    file.open(QFile::WriteOnly);
-    file.close();
-}
-
-static QString baseTestDir()
-{
-    return Utils::TemporaryDirectory::masterDirectoryPath() + "/qtc_cppheadersource/";
-}
-
-namespace CppEditor::Internal {
-
-void HeaderSourceTest::test()
-{
-    QFETCH(QString, sourceFileName);
-    QFETCH(QString, headerFileName);
-
-    CppEditor::Tests::TemporaryDir temporaryDir;
-    QVERIFY(temporaryDir.isValid());
-
-    const QDir path = QDir(temporaryDir.path() + QLatin1Char('/') + _(QTest::currentDataTag()));
-    const FilePath sourcePath = FilePath::fromString(path.absoluteFilePath(sourceFileName));
-    const FilePath headerPath = FilePath::fromString(path.absoluteFilePath(headerFileName));
-    createTempFile(sourcePath);
-    createTempFile(headerPath);
-
-    bool wasHeader;
-    clearHeaderSourceCache();
-    QCOMPARE(correspondingHeaderOrSource(sourcePath, &wasHeader), headerPath);
-    QVERIFY(!wasHeader);
-    clearHeaderSourceCache();
-    QCOMPARE(correspondingHeaderOrSource(headerPath, &wasHeader), sourcePath);
-    QVERIFY(wasHeader);
-}
-
-void HeaderSourceTest::test_data()
-{
-    QTest::addColumn<QString>("sourceFileName");
-    QTest::addColumn<QString>("headerFileName");
-    QTest::newRow("samedir") << _("foo.cpp") << _("foo.h");
-    QTest::newRow("includesub") << _("foo.cpp") << _("include/foo.h");
-    QTest::newRow("headerprefix") << _("foo.cpp") << _("testh_foo.h");
-    QTest::newRow("sourceprefixwsub") << _("testc_foo.cpp") << _("include/foo.h");
-    QTest::newRow("sourceAndHeaderPrefixWithBothsub") << _("src/testc_foo.cpp") << _("include/testh_foo.h");
-}
-
-void HeaderSourceTest::initTestCase()
-{
-    QDir(baseTestDir()).mkpath(_("."));
-    CppFileSettings &fs = globalCppFileSettings();
-    fs.headerSearchPaths.append(QLatin1String("include"));
-    fs.headerSearchPaths.append(QLatin1String("../include"));
-    fs.sourceSearchPaths.append(QLatin1String("src"));
-    fs.sourceSearchPaths.append(QLatin1String("../src"));
-    fs.headerPrefixes.append(QLatin1String("testh_"));
-    fs.sourcePrefixes.append(QLatin1String("testc_"));
-}
-
-void HeaderSourceTest::cleanupTestCase()
-{
-    Utils::FilePath::fromString(baseTestDir()).removeRecursively();
-    CppFileSettings &fs = globalCppFileSettings();
-    fs.headerSearchPaths.removeLast();
-    fs.headerSearchPaths.removeLast();
-    fs.sourceSearchPaths.removeLast();
-    fs.sourceSearchPaths.removeLast();
-    fs.headerPrefixes.removeLast();
-    fs.sourcePrefixes.removeLast();
-}
-
-} // namespace CppEditor::Internal
diff --git a/src/plugins/cppeditor/cppheadersource_test.h b/src/plugins/cppeditor/cppheadersource_test.h
deleted file mode 100644
index 5f11c0272e..0000000000
--- a/src/plugins/cppeditor/cppheadersource_test.h
+++ /dev/null
@@ -1,22 +0,0 @@
-// Copyright (C) 2021 The Qt Company Ltd.
-// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
-
-#pragma once
-
-#include <QObject>
-
-namespace CppEditor::Internal {
-
-class HeaderSourceTest : public QObject
-{
-    Q_OBJECT
-
-private slots:
-    void initTestCase();
-    void cleanupTestCase();
-
-    void test_data();
-    void test();
-};
-
-} // namespace CppEditor::Internal
diff --git a/src/plugins/cppeditor/cppinsertvirtualmethods.cpp b/src/plugins/cppeditor/cppinsertvirtualmethods.cpp
index fd76b8522a..50a9c2c48a 100644
--- a/src/plugins/cppeditor/cppinsertvirtualmethods.cpp
+++ b/src/plugins/cppeditor/cppinsertvirtualmethods.cpp
@@ -40,7 +40,6 @@
 #include <QVBoxLayout>
 
 #ifdef WITH_TESTS
-#include "cppeditorplugin.h"
 #include "cppquickfix_test.h"
 #include <QtTest>
 #endif
diff --git a/src/plugins/cppeditor/cpplocatorfilter.cpp b/src/plugins/cppeditor/cpplocatorfilter.cpp
index c6d1be6663..8fab8f4dcd 100644
--- a/src/plugins/cppeditor/cpplocatorfilter.cpp
+++ b/src/plugins/cppeditor/cpplocatorfilter.cpp
@@ -4,7 +4,6 @@
 #include "cpplocatorfilter.h"
 
 #include "cppeditorconstants.h"
-#include "cppeditorplugin.h"
 #include "cppeditortr.h"
 #include "cpplocatordata.h"
 #include "cppmodelmanager.h"
diff --git a/src/plugins/cppeditor/cppquickfix_test.cpp b/src/plugins/cppeditor/cppquickfix_test.cpp
index 3b3d88f149..b0064ab790 100644
--- a/src/plugins/cppeditor/cppquickfix_test.cpp
+++ b/src/plugins/cppeditor/cppquickfix_test.cpp
@@ -4,7 +4,6 @@
 #include "cppquickfix_test.h"
 
 #include "cppcodestylepreferences.h"
-#include "cppeditorplugin.h"
 #include "cppeditorwidget.h"
 #include "cppmodelmanager.h"
 #include "cppquickfixassistant.h"
diff --git a/src/plugins/cppeditor/cpptoolsjsextension.cpp b/src/plugins/cppeditor/cpptoolsjsextension.cpp
index e5b3499a96..607744eec1 100644
--- a/src/plugins/cppeditor/cpptoolsjsextension.cpp
+++ b/src/plugins/cppeditor/cpptoolsjsextension.cpp
@@ -3,7 +3,6 @@
 
 #include "cpptoolsjsextension.h"
 
-#include "cppeditorplugin.h"
 #include "cppfilesettingspage.h"
 #include "cpplocatordata.h"
 #include "cppworkingcopy.h"
diff --git a/src/plugins/cppeditor/fileandtokenactions_test.cpp b/src/plugins/cppeditor/fileandtokenactions_test.cpp
index ca6411116f..f341cc1808 100644
--- a/src/plugins/cppeditor/fileandtokenactions_test.cpp
+++ b/src/plugins/cppeditor/fileandtokenactions_test.cpp
@@ -3,14 +3,11 @@
 
 #include "fileandtokenactions_test.h"
 
-#include "cppeditorplugin.h"
 #include "cppeditorwidget.h"
 #include "cppquickfix.h"
 #include "cppquickfixassistant.h"
-#include "cppquickfixes.h"
 #include "cppinsertvirtualmethods.h"
 #include "cppmodelmanager.h"
-#include "cpptoolsreuse.h"
 #include "cpptoolstestcase.h"
 #include "cpptypehierarchy.h"
 #include "cppworkingcopy.h"
diff --git a/src/plugins/cppeditor/followsymbol_switchmethoddecldef_test.cpp b/src/plugins/cppeditor/followsymbol_switchmethoddecldef_test.cpp
index 0c06f86783..d18e8dc391 100644
--- a/src/plugins/cppeditor/followsymbol_switchmethoddecldef_test.cpp
+++ b/src/plugins/cppeditor/followsymbol_switchmethoddecldef_test.cpp
@@ -4,12 +4,9 @@
 #include "followsymbol_switchmethoddecldef_test.h"
 
 #include "cppcodemodelsettings.h"
-#include "cppeditorplugin.h"
 #include "cppeditorwidget.h"
-#include "cppelementevaluator.h"
 #include "cppfollowsymbolundercursor.h"
 #include "cppmodelmanager.h"
-#include "cpptoolsreuse.h"
 #include "cpptoolstestcase.h"
 #include "cppvirtualfunctionassistprovider.h"
 #include "cppvirtualfunctionproposalitem.h"
diff --git a/src/plugins/designer/qtcreatorintegration.cpp b/src/plugins/designer/qtcreatorintegration.cpp
index 0428067105..267e0ddeeb 100644
--- a/src/plugins/designer/qtcreatorintegration.cpp
+++ b/src/plugins/designer/qtcreatorintegration.cpp
@@ -12,7 +12,6 @@
 #include <designer/cpp/formclasswizardpage.h>
 
 #include <cppeditor/cppeditorconstants.h>
-#include <cppeditor/cppeditorplugin.h>
 #include <cppeditor/cppeditorwidget.h>
 #include <cppeditor/cppmodelmanager.h>
 #include <cppeditor/cppsemanticinfo.h>