Compute fg and bg colors for setEditable for StyledText

This commit adds the foreground and background color computation for
setEditable. Earlier this was handled only for setEnabled. This commit
also adds a different foreground and background color for StyledText
when background is not editable.

Fixes :#3132

Author: elsazac

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledText.java

@@ -8290,8 +8290,10 @@ public void setBackground(Color color) {
 	customBackground = color != null && !this.insideSetEnableCall && !backgroundDisabled;
 	background = color;
 	super.setBackground(color);
-	resetCache(0, content.getLineCount());
-	setCaretLocations();
+	if (content != null) {
+		resetCache(0, content.getLineCount());
+		setCaretLocations();
+	}
 	super.redraw();
 }
 /**
@@ -8772,6 +8774,41 @@ public void setDragDetect (boolean dragDetect) {
 	checkWidget ();
 	this.dragDetect = dragDetect;
 }
+
+/**
+ * Applies foreground and background colors based on the control's state.
+ * Custom foreground and background settings are preserved and not overridden.
+ *
+ * @param enabled  {@code true} if the control is enabled; {@code false} otherwise
+ * @param editable {@code true} if the control is editable; {@code false} otherwise
+ * @since 3.134
+ *
+ */
+protected void updateColors(boolean enabled, boolean editable) {
+	this.insideSetEnableCall = true;
+	Display display = getDisplay();
+	try {
+		if (enabled && editable) {
+			if (!customBackground)
+				setBackground(display.getSystemColor(SWT.COLOR_LIST_BACKGROUND));
+			if (!customForeground)
+				setForeground(display.getSystemColor(SWT.COLOR_LIST_FOREGROUND));
+		} else if (!enabled) {
+			if (!customBackground)
+				setBackground(display.getSystemColor(SWT.COLOR_TEXT_DISABLED_BACKGROUND));
+			if (!customForeground)
+				setForeground(display.getSystemColor(SWT.COLOR_WIDGET_DISABLED_FOREGROUND));
+		} else if (!editable) {
+			if (!customBackground)
+				setBackground(display.getSystemColor(SWT.COLOR_TITLE_INACTIVE_BACKGROUND));
+			if (!customForeground)
+				setForeground(display.getSystemColor(SWT.COLOR_GRAY));
+		}
+	} finally {
+		this.insideSetEnableCall = false;
+	}
+}
+
 /**
  * Sets whether the widget content can be edited.
  *
@@ -8785,28 +8822,13 @@ public void setDragDetect (boolean dragDetect) {
 public void setEditable(boolean editable) {
 	checkWidget();
 	this.editable = editable;
+	updateColors(this.enabled, this.editable);
 }
 @Override
 public void setEnabled(boolean enabled) {
 	super.setEnabled(enabled);
-	Display display = getDisplay();
 	this.enabled = enabled;
-	this.insideSetEnableCall = true;
-	try {
-		if (enabled && editable) {
-			if (!customBackground) setBackground(display.getSystemColor(SWT.COLOR_LIST_BACKGROUND));
-			if (!customForeground) setForeground(display.getSystemColor(SWT.COLOR_LIST_FOREGROUND));
-		} else if(!enabled) {
-			if (!customBackground) setBackground(display.getSystemColor(SWT.COLOR_TEXT_DISABLED_BACKGROUND));
-			if (!customForeground) setForeground(display.getSystemColor(SWT.COLOR_WIDGET_DISABLED_FOREGROUND));
-		} else if(!editable) {
-			if (!customBackground) setBackground(display.getSystemColor(SWT.COLOR_TEXT_DISABLED_BACKGROUND));
-			if (!customForeground) setForeground(display.getSystemColor(SWT.COLOR_LIST_FOREGROUND));
-		}
-	}
-	finally {
-		this.insideSetEnableCall = false;
-	}
+	updateColors(this.enabled, this.editable);
 }
 
 @Override
@@ -8885,8 +8907,10 @@ public void setForeground(Color color) {
 	customForeground = color != null && !this.insideSetEnableCall && !foregroundDisabled;
 	foreground = color;
 	super.setForeground(color);
-	resetCache(0, content.getLineCount());
-	setCaretLocations();
+	if (content != null) {
+		resetCache(0, content.getLineCount());
+		setCaretLocations();
+	}
 	super.redraw();
 }
 /**