Comply with rule-of-three

The rule-of-three says that if any of virtual destructor, copy constructor
or assignment operator needs to be manually implemented, then all three
should be implemented. Otherwise you can get subtle bugs which can be
difficult to find. In the changed classes, changing a copy-construction to
an assignment would have had surprising effects. Now they all behave
consistently.

src/insets/InsetCommand.cpp

@@ -65,6 +65,20 @@ InsetCommand::InsetCommand(InsetCommand const & rhs)
 {}
 
 
+InsetCommand & InsetCommand::operator=(InsetCommand const & rhs)
+{
+	if (&rhs == this)
+		return *this;
+
+	Inset::operator=(rhs);
+	p_ = rhs.p_;
+	mouse_hover_.clear();
+	button_ = RenderButton();
+
+	return *this;
+}
+
+
 InsetCommand::~InsetCommand()
 {
 	if (p_.code() != NO_CODE)

src/insets/InsetCommand.h

@@ -39,6 +39,8 @@ public:
 	///
 	InsetCommand(InsetCommand const & rhs);
 	///
+	InsetCommand & operator=(InsetCommand const & rhs);
+	///
 	virtual ~InsetCommand();
 	///
 	InsetCommand * asInsetCommand() { return this; }

src/insets/InsetIPA.cpp

@@ -54,6 +54,18 @@ InsetIPA::InsetIPA(InsetIPA const & other)
 }
 
 
+InsetIPA & InsetIPA::operator=(InsetIPA const & other)
+{
+	if (&other == this)
+		return *this;
+
+	InsetText::operator=(other);
+	preview_.reset(new RenderPreview(*other.preview_, this));
+
+	return *this;
+}
+
+
 void InsetIPA::write(ostream & os) const
 {
 	os << "IPA" << "\n";

src/insets/InsetIPA.h

@@ -36,6 +36,8 @@ public:
 	~InsetIPA();
 	///
 	InsetIPA(InsetIPA const & other);
+	///
+	InsetIPA & operator=(InsetIPA const & other);
 
 	/// \name Methods inherited from Inset class
 	//@{

src/insets/InsetInclude.h

@@ -35,6 +35,10 @@ namespace support {
 
 /// for including tex/lyx files
 class InsetInclude : public InsetCommand {
+	// Disable assignment operator, since it is not used, and cannot be
+	// implemented consistently with the copy constructor, because
+	// include_label is const.
+	InsetInclude & operator=(InsetInclude const &);
 public:
 	///
 	InsetInclude(Buffer * buf, InsetCommandParams const &);

src/insets/InsetPreview.cpp

@@ -54,6 +54,18 @@ InsetPreview::InsetPreview(InsetPreview const & other)
 }
 
 
+InsetPreview & InsetPreview::operator=(InsetPreview const & other)
+{
+	if (&other == this)
+		return *this;
+
+	InsetText::operator=(other);
+	preview_.reset(new RenderPreview(*other.preview_, this));
+
+	return *this;
+}
+
+
 void InsetPreview::write(ostream & os) const
 {
 	os << "Preview" << "\n";

src/insets/InsetPreview.h

@@ -36,6 +36,8 @@ public:
 	~InsetPreview();
 	///
 	InsetPreview(InsetPreview const & other);
+	///
+	InsetPreview & operator=(InsetPreview const & other);
 
 	/// \name Methods inherited from Inset class
 	//@{