"New Class" wizard: Try to find a base class header

If the project has a header file whose name suggests that it might
declare the base class, then add an include statement for it.
While we cannot guarantee that the include statement is resolvable as-
is, it's at least a basis for the user to adapt accordingly, while
without any include statement the class will definitely not compile.

Fixes: QTCREATORBUG-3855
Change-Id: I55ec43d58a9a13b9b59a5bbe6415a457b974b654
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

share/qtcreator/templates/wizards/classes/cpp/file.h

@@ -6,6 +6,7 @@
 #define %{GUARD}
 @endif
 
+%{JS: Cpp.includeStatement('%{Base}', Util.preferredSuffix('text/x-c++hdr'), ['QObject', 'QWidget', 'QMainWindow', 'QQuickItem', 'QSharedData'], '%{TargetPath}')}\
 %{JS: QtSupport.qtIncludes([ ( '%{IncludeQObject}' )          ? 'QtCore/%{IncludeQObject}'                 : '',
                              ( '%{IncludeQWidget}' )          ? 'QtGui/%{IncludeQWidget}'                  : '',
                              ( '%{IncludeQMainWindow}' )      ? 'QtGui/%{IncludeQMainWindow}'              : '',

src/plugins/cpptools/cpptoolsjsextension.cpp

@@ -29,10 +29,15 @@
 
 #include <coreplugin/icore.h>
 
+#include <projectexplorer/project.h>
+#include <projectexplorer/projectnodes.h>
+#include <projectexplorer/session.h>
+
 #include <utils/codegeneration.h>
 #include <utils/fileutils.h>
 
 #include <QFileInfo>
+#include <QStringList>
 #include <QTextStream>
 
 namespace CppTools {
@@ -113,5 +118,69 @@ QString CppToolsJsExtension::closeNamespaces(const QString &klass) const
     return result;
 }
 
+QString CppToolsJsExtension::includeStatement(
+        const QString &fullyQualifiedClassName,
+        const QString &suffix,
+        const QString &specialClasses,
+        const QString &pathOfIncludingFile
+        )
+{
+    if (fullyQualifiedClassName.isEmpty())
+        return {};
+    const QString className = parts(fullyQualifiedClassName).last();
+    if (className.isEmpty() || specialClasses.contains(className))
+        return {};
+    if (className.startsWith('Q') && className.length() > 2 && className.at(1).isUpper())
+        return "#include <" + className + ">\n";
+    const auto withUnderScores = [&className] {
+        QString baseName = className;
+        baseName[0] = baseName[0].toLower();
+        for (int i = 1; i < baseName.length(); ++i) {
+            if (baseName[i].isUpper()) {
+                baseName.insert(i, '_');
+                baseName[i + 1] = baseName[i + 1].toLower();
+                ++i;
+            }
+        }
+        return baseName;
+    };
+    QStringList candidates{className + '.' + suffix};
+    bool hasUpperCase = false;
+    bool hasLowerCase = false;
+    for (int i = 0; i < className.length() && (!hasUpperCase || !hasLowerCase); ++i) {
+        if (className.at(i).isUpper())
+            hasUpperCase = true;
+        if (className.at(i).isLower())
+            hasLowerCase = true;
+    }
+    if (hasUpperCase)
+        candidates << className.toLower() + '.' + suffix;
+    if (hasUpperCase && hasLowerCase)
+        candidates << withUnderScores()  + '.' + suffix;
+    candidates.removeDuplicates();
+    using namespace ProjectExplorer;
+    const auto nodeMatchesFileName = [&candidates](Node *n) {
+        if (const FileNode * const fileNode = n->asFileNode()) {
+            if (fileNode->fileType() == FileType::Header
+                && candidates.contains(fileNode->filePath().fileName())) {
+                return true;
+            }
+        }
+        return false;
+    };
+    for (const Project * const p : SessionManager::projects()) {
+        const Node *theNode = p->rootProjectNode()->findNode(nodeMatchesFileName);
+        if (theNode) {
+            const bool sameDir = pathOfIncludingFile == theNode->filePath().toFileInfo().path();
+            return QString("#include ")
+                    .append(sameDir ? '"' : '<')
+                    .append(theNode->filePath().fileName())
+                    .append(sameDir ? '"' : '>')
+                    .append('\n');
+        }
+    }
+    return {};
+}
+
 } // namespace Internal
 } // namespace CppTools

src/plugins/cpptools/cpptoolsjsextension.h

@@ -55,6 +55,14 @@ public:
     Q_INVOKABLE QString classToHeaderGuard(const QString &klass, const QString &extension) const;
     Q_INVOKABLE QString openNamespaces(const QString &klass) const;
     Q_INVOKABLE QString closeNamespaces(const QString &klass) const;
+
+    // Find header file for class.
+    Q_INVOKABLE QString includeStatement(
+            const QString &fullyQualifiedClassName,
+            const QString &suffix,
+            const QString &specialClasses,
+            const QString &pathOfIncludingFile
+            );
 };
 
 } // namespace Internal