Clarified comments around the JUCE_ALLOW_STATIC_NULL_VARIABLES items to make clear that they're deprecated

modules/juce_core/containers/juce_NamedValueSet.cpp

@@ -120,12 +120,8 @@ bool NamedValueSet::isEmpty() const noexcept    { return values.isEmpty(); }
 
 static const var& getNullVarRef() noexcept
 {
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    return var::null;
-   #else
     static var nullVar;
     return nullVar;
-   #endif
 }
 
 const var& NamedValueSet::operator[] (const Identifier& name) const noexcept

modules/juce_core/containers/juce_Variant.h

@@ -64,11 +64,6 @@ public:
     /** Destructor. */
     ~var() noexcept;
 
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    /** A static var object that can be used where you need an empty variant object. */
-    static const var null;
-   #endif
-
     var (const var& valueToCopy);
     var (int value) noexcept;
     var (int64 value) noexcept;
@@ -277,6 +272,18 @@ public:
     */
     static var readFromStream (InputStream& input);
 
+   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
+    /** This was a static empty var object, but is now deprecated as it's too easy to accidentally
+        use it indirectly during a static constructor, leading to hard-to-find order-of-initialisation
+        problems.
+        @deprecated If you need a default-constructed var, just use var() or {}.
+        The only time you might miss having var::null available might be if you need to return an
+        empty var from a function by reference, but if you need to do that, it's easy enough to use
+        a function-local static var and return that, avoiding any order-of-initialisation issues.
+    */
+    static const var null;
+   #endif
+
 private:
     //==============================================================================
     class VariantType;            friend class VariantType;

modules/juce_core/files/juce_File.h

@@ -87,15 +87,6 @@ public:
     /** Move assignment operator */
     File& operator= (File&&) noexcept;
 
-    //==============================================================================
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    /** This static constant is used for referring to an 'invalid' file.
-        Bear in mind that you should avoid this kind of static variable, and always prefer
-        to use File() or {} if you need a default-constructed File object.
-    */
-    static const File nonexistent;
-   #endif
-
     //==============================================================================
     /** Checks whether the file actually exists.
 
@@ -1037,6 +1028,16 @@ public:
     JUCE_DEPRECATED (static const StringRef separatorString);
    #endif
 
+    //==============================================================================
+   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
+    /** This was a static empty File object, but is now deprecated as it's too easy to accidentally
+        use it indirectly during a static constructor, leading to hard-to-find order-of-initialisation
+        problems.
+        @deprecated If you need a default-constructed File object, just use File() or {}.
+    */
+    static const File nonexistent;
+   #endif
+
 private:
     //==============================================================================
     String fullPath;

modules/juce_core/text/juce_String.h

@@ -138,17 +138,6 @@ public:
     /** Destructor. */
     ~String() noexcept;
 
-    //==============================================================================
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    /** This is a static empty string object that can be used if you need a reference to one.
-        The value of String::empty is exactly the same as String(), and in almost all cases
-        it's better to avoid String::empty and just use String() or {} instead, so that the compiler
-        only has to reason about locally-constructed objects, rather than taking into account
-        the fact that you're referencing a global shared static memory address.
-    */
-    static const String empty;
-   #endif
-
     /** This is the character encoding type used internally to store the string.
 
         By setting the value of JUCE_STRING_UTF_TYPE to 8, 16, or 32, you can change the
@@ -1247,6 +1236,19 @@ public:
     */
     int getReferenceCount() const noexcept;
 
+    //==============================================================================
+   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
+    /** This was a static empty string object, but is now deprecated as it's too easy to accidentally
+        use it indirectly during a static constructor, leading to hard-to-find order-of-initialisation
+        problems.
+        @deprecated If you need an empty String object, just use String() or {}.
+        The only time you might miss having String::empty available might be if you need to return an
+        empty string from a function by reference, but if you need to do that, it's easy enough to use
+        a function-local static String object and return that, avoiding any order-of-initialisation issues.
+    */
+    static const String empty;
+   #endif
+
 private:
     //==============================================================================
     CharPointerType text;

modules/juce_core/text/juce_StringArray.cpp

@@ -120,12 +120,8 @@ const String& StringArray::operator[] (int index) const noexcept
     if (isPositiveAndBelow (index, strings.size()))
         return strings.getReference (index);
 
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    return String::empty;
-   #else
     static String empty;
     return empty;
-   #endif
 }
 
 String& StringArray::getReference (int index) noexcept

modules/juce_core/xml/juce_XmlElement.cpp

@@ -447,12 +447,8 @@ int XmlElement::getNumAttributes() const noexcept
 
 static const String& getEmptyStringRef() noexcept
 {
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    return String::empty;
-   #else
     static String empty;
     return empty;
-   #endif
 }
 
 const String& XmlElement::getAttributeName (const int index) const noexcept

modules/juce_data_structures/values/juce_ValueTree.cpp

@@ -688,12 +688,8 @@ ValueTree ValueTree::getSibling (int delta) const noexcept
 
 static const var& getNullVarRef() noexcept
 {
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    return var::null;
-   #else
     static var nullVar;
     return nullVar;
-   #endif
 }
 
 const var& ValueTree::operator[] (const Identifier& name) const noexcept

modules/juce_data_structures/values/juce_ValueTree.h

@@ -532,19 +532,18 @@ public:
         }
     }
 
+    /** Returns the total number of references to the shared underlying data structure that this
+        ValueTree is using.
+    */
+    int getReferenceCount() const noexcept;
+
    #if JUCE_ALLOW_STATIC_NULL_VARIABLES
     /** An invalid ValueTree that can be used if you need to return one as an error condition, etc.
-        This invalid object is equivalent to ValueTree created with its default constructor, but
-        you should always prefer to avoid it and use ValueTree() or {} instead.
+        @deprecated If you need an empty ValueTree object, just use ValueTree() or {}.
     */
     static const ValueTree invalid;
    #endif
 
-    /** Returns the total number of references to the shared underlying data structure that this
-        ValueTree is using.
-    */
-    int getReferenceCount() const noexcept;
-
 private:
     //==============================================================================
     JUCE_PUBLIC_IN_DLL_BUILD (class SharedObject)

modules/juce_graphics/geometry/juce_AffineTransform.h

@@ -68,20 +68,12 @@ public:
     /** Compares two transforms. */
     bool operator!= (const AffineTransform& other) const noexcept;
 
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    /** A ready-to-use identity transform.
-        Note that you should always avoid using a static variable like this, and
-        prefer AffineTransform() or {} if you need a default-constructed instance.
-    */
-    static const AffineTransform identity;
-   #endif
-
     //==============================================================================
     /** Transforms a 2D coordinate using this matrix. */
     template <typename ValueType>
     void transformPoint (ValueType& x, ValueType& y) const noexcept
     {
-        const ValueType oldX = x;
+        auto oldX = x;
         x = static_cast<ValueType> (mat00 * oldX + mat01 * y + mat02);
         y = static_cast<ValueType> (mat10 * oldX + mat11 * y + mat12);
     }
@@ -95,7 +87,7 @@ public:
     void transformPoints (ValueType& x1, ValueType& y1,
                           ValueType& x2, ValueType& y2) const noexcept
     {
-        const ValueType oldX1 = x1, oldX2 = x2;
+        auto oldX1 = x1, oldX2 = x2;
         x1 = static_cast<ValueType> (mat00 * oldX1 + mat01 * y1 + mat02);
         y1 = static_cast<ValueType> (mat10 * oldX1 + mat11 * y1 + mat12);
         x2 = static_cast<ValueType> (mat00 * oldX2 + mat01 * y2 + mat02);
@@ -112,7 +104,7 @@ public:
                           ValueType& x2, ValueType& y2,
                           ValueType& x3, ValueType& y3) const noexcept
     {
-        const ValueType oldX1 = x1, oldX2 = x2, oldX3 = x3;
+        auto oldX1 = x1, oldX2 = x2, oldX3 = x3;
         x1 = static_cast<ValueType> (mat00 * oldX1 + mat01 * y1 + mat02);
         y1 = static_cast<ValueType> (mat10 * oldX1 + mat11 * y1 + mat12);
         x2 = static_cast<ValueType> (mat00 * oldX2 + mat01 * y2 + mat02);
@@ -276,6 +268,13 @@ public:
     */
     float getScaleFactor() const noexcept;
 
+   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
+    /** A ready-to-use identity transform - now depracated.
+        @deprecated If you need an identity transform, just use AffineTransform() or {}.
+    */
+    static const AffineTransform identity;
+   #endif
+
     //==============================================================================
     /* The transform matrix is:
 

modules/juce_graphics/images/juce_Image.h

@@ -153,14 +153,6 @@ public:
     */
     inline bool isNull() const noexcept                     { return image == nullptr; }
 
-   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
-    /** A null Image object that can be used when you need to return an invalid image.
-        This object is the equivalient to an Image created with the default constructor, and
-        you should always prefer to use Image() or {} when you need an empty image object.
-    */
-    static const Image null;
-   #endif
-
     //==============================================================================
     /** Returns the image's width (in pixels). */
     int getWidth() const noexcept;
@@ -420,6 +412,13 @@ public:
     /** @internal */
     explicit Image (ImagePixelData*) noexcept;
 
+   #if JUCE_ALLOW_STATIC_NULL_VARIABLES
+    /** A null Image object that can be used when you need to return an invalid image.
+        @deprecated If you need a default-constructed var, just use Image() or {}.
+    */
+    static const Image null;
+   #endif
+
 private:
     //==============================================================================
     ReferenceCountedObjectPtr<ImagePixelData> image;

modules/juce_gui_basics/juce_gui_basics.h

@@ -117,8 +117,6 @@ namespace juce
     class MouseInputSource;
     class MouseInputSourceInternal;
     class ComponentPeer;
-    class MarkerList;
-    class RelativeRectangle;
     class MouseEvent;
     struct MouseWheelDetails;
     struct PenDetails;
@@ -130,28 +128,21 @@ namespace juce
     class ComboBox;
     class Button;
     class FilenameComponent;
-    class DocumentWindow;
     class ResizableWindow;
-    class GroupComponent;
     class MenuBarComponent;
-    class DropShadower;
     class GlyphArrangement;
-    class PropertyComponent;
     class TableHeaderComponent;
     class Toolbar;
-    class ToolbarItemComponent;
     class PopupMenu;
     class ProgressBar;
     class FileBrowserComponent;
     class DirectoryContentsDisplayComponent;
     class FilePreviewComponent;
-    class ImageButton;
     class CallOutBox;
     class Drawable;
     class DrawablePath;
     class DrawableComposite;
     class CaretComponent;
-    class BubbleComponent;
     class KeyPressMappingSet;
     class ApplicationCommandManagerListener;
     class DrawableButton;