Don't show code folding margin when it isn't supported

Introduce setCodeFoldingSupported to the BaseTextEditor, and only
enabled it for the C++ and QtScript editors. This removes the useless
margin meant for code folding markers from the plain text editor and
.pro file editor.

src/plugins/cppeditor/cppeditor.cpp

@@ -185,6 +185,7 @@ CPPEditor::CPPEditor(QWidget *parent)
 {
     setParenthesesMatchingEnabled(true);
     setMarksVisible(true);
+    setCodeFoldingSupported(true);
     setCodeFoldingVisible(true);
     baseTextDocument()->setSyntaxHighlighter(new CppHighlighter);
 //    new QShortcut(QKeySequence("Ctrl+Alt+M"), this, SLOT(foo()), 0, Qt::WidgetShortcut);

src/plugins/qtscripteditor/qtscripteditor.cpp

@@ -49,7 +49,6 @@ namespace Internal {
 ScriptEditorEditable::ScriptEditorEditable(ScriptEditor *editor, const QList<int>& context)
     : BaseTextEditorEditable(editor), m_context(context)
 {
-
 }
 
 ScriptEditor::ScriptEditor(const Context &context,
@@ -61,6 +60,7 @@ ScriptEditor::ScriptEditor(const Context &context,
 {
     setParenthesesMatchingEnabled(true);
     setMarksVisible(true);
+    setCodeFoldingSupported(true);
     setCodeFoldingVisible(true);
     setMimeType(QtScriptEditor::Constants::C_QTSCRIPTEDITOR_MIMETYPE);
 

src/plugins/texteditor/basetexteditor.cpp

@@ -1198,7 +1198,7 @@ bool BaseTextEditor::lineSeparatorsAllowed() const
 
 void BaseTextEditor::setCodeFoldingVisible(bool b)
 {
-    d->m_codeFoldingVisible = b;
+    d->m_codeFoldingVisible = b && d->m_codeFoldingSupported;
     slotUpdateExtraAreaWidth();
 }
 
@@ -1207,6 +1207,22 @@ bool BaseTextEditor::codeFoldingVisible() const
     return d->m_codeFoldingVisible;
 }
 
+/**
+ * Sets whether code folding is supported by the syntax highlighter. When not
+ * supported (the default), this makes sure the code folding is not shown.
+ *
+ * Needs to be called before calling setCodeFoldingVisible.
+ */
+void BaseTextEditor::setCodeFoldingSupported(bool b)
+{
+    d->m_codeFoldingSupported = b;
+}
+
+bool BaseTextEditor::codeFoldingSupported() const
+{
+    return d->m_codeFoldingSupported;
+}
+
 void BaseTextEditor::setRevisionsVisible(bool b)
 {
     d->m_revisionsVisible = b;
@@ -1294,6 +1310,7 @@ BaseTextEditorPrivate::BaseTextEditorPrivate()
     m_extraArea(0),
     m_marksVisible(false),
     m_codeFoldingVisible(false),
+    m_codeFoldingSupported(false),
     m_revisionsVisible(false),
     m_lineNumbersVisible(true),
     m_highlightCurrentLine(true),

src/plugins/texteditor/basetexteditor.h

@@ -68,6 +68,7 @@ struct StorageSettings;
 
 struct Parenthesis;
 typedef QVector<Parenthesis> Parentheses;
+
 struct TEXTEDITOR_EXPORT Parenthesis
 {
     enum Type { Opened, Closed };
@@ -84,7 +85,6 @@ struct TEXTEDITOR_EXPORT Parenthesis
 };
 
 
-
 class TEXTEDITOR_EXPORT TextBlockUserData : public QTextBlockUserData
 {
 public:
@@ -285,6 +285,9 @@ public:
     void setCodeFoldingVisible(bool b);
     bool codeFoldingVisible() const;
 
+    void setCodeFoldingSupported(bool b);
+    bool codeFoldingSupported() const;
+
     void setRevisionsVisible(bool b);
     bool revisionsVisible() const;
 

src/plugins/texteditor/basetexteditor_p.h

@@ -180,6 +180,7 @@ public:
     void updateMarksBlock(const QTextBlock &block);
     uint m_marksVisible : 1;
     uint m_codeFoldingVisible : 1;
+    uint m_codeFoldingSupported : 1;
     uint m_revisionsVisible : 1;
     uint m_lineNumbersVisible : 1;
     uint m_highlightCurrentLine : 1;