Improve 'Selection' exception messages.

Source/core/page/DOMSelection.cpp

Index: Source/core/page/DOMSelection.cpp
diff --git a/Source/core/page/DOMSelection.cpp b/Source/core/page/DOMSelection.cpp
index f26d1faf09a2082e36b8c049893b594bad9be3a5..39d10d84158854f2493a4b6d814e72dcdd83ddac 100644
--- a/Source/core/page/DOMSelection.cpp
+++ b/Source/core/page/DOMSelection.cpp
@@ -199,7 +199,7 @@ void DOMSelection::collapse(Node* node, int offset, ExceptionState& es)
         return;
 
     if (offset < 0) {
-        es.throwDOMException(IndexSizeError);
+        es.throwDOMException(IndexSizeError, "Failed to execute 'collapse' on a 'Selection' object: " + String::number(offset) + " is not a valid offset.");
         return;
     }
 
@@ -218,7 +218,7 @@ void DOMSelection::collapseToEnd(ExceptionState& es)
     const VisibleSelection& selection = m_frame->selection()->selection();
 
     if (selection.isNone()) {
-        es.throwDOMException(InvalidStateError);
+        es.throwDOMException(InvalidStateError, "Failed to execute 'collapseToEnd' on a 'Selection' object: there is no selection.");

[arv (Not doing code reviews), 2013/08/13 13:57:31]

I feel like we are repeating ourselves a lot. Maybe use String::format?

es.throwDOMException(InvalidStateError, String::format(failedToExecutePattern,
"collapseToEnd", "Selection", "there is no selection"));

where pattern is defined somewhere where it can be reused

failedToExecutePattern = "Failed to execute '%s' on a '%s' object: %s."

[Mike West, 2013/08/13 14:00:17]

I can do that. I have vague performance reluctance to use String::format, but
given the rarity with which exceptions should be thrown, I guess it's nothing to
really worry about.

[arv (Not doing code reviews), 2013/08/13 14:07:49]

Yeah, I don't think we need to optimize for the exception case ;-)

         return;
     }
 
@@ -233,7 +233,7 @@ void DOMSelection::collapseToStart(ExceptionState& es)
     const VisibleSelection& selection = m_frame->selection()->selection();
 
     if (selection.isNone()) {
-        es.throwDOMException(InvalidStateError);
+        es.throwDOMException(InvalidStateError, "Failed to execute 'collapseToStart' on a 'Selection' object: there is no selection.");
         return;
     }
 
@@ -252,8 +252,13 @@ void DOMSelection::setBaseAndExtent(Node* baseNode, int baseOffset, Node* extent
     if (!m_frame)
         return;
 
-    if (baseOffset < 0 || extentOffset < 0) {
-        es.throwDOMException(IndexSizeError);
+    if (baseOffset < 0) {
+        es.throwDOMException(IndexSizeError, "Failed to execute 'setBaseAndExtent' on a 'Selection' object: " + String::number(baseOffset) + " is not a valid base offset.");
+        return;
+    }
+
+    if (extentOffset < 0) {
+        es.throwDOMException(IndexSizeError, "Failed to execute 'setBaseAndExtent' on a 'Selection' object: " + String::number(extentOffset) + " is not a valid extent offset.");
         return;
     }
 
@@ -272,7 +277,7 @@ void DOMSelection::setPosition(Node* node, int offset, ExceptionState& es)
     if (!m_frame)
         return;
     if (offset < 0) {
-        es.throwDOMException(IndexSizeError);
+        es.throwDOMException(IndexSizeError, "Failed to execute 'setPosition' on a 'Selection' object: " + String::number(offset) + " is not a valid offset.");
         return;
     }
 
@@ -339,12 +344,16 @@ void DOMSelection::extend(Node* node, int offset, ExceptionState& es)
         return;
 
     if (!node) {
-        es.throwDOMException(TypeMismatchError);
+        es.throwDOMException(TypeMismatchError, "Failed to execute 'extend' on a 'Selection' object: The node provided is invalid.");
         return;
     }
 
-    if (offset < 0 || offset > (node->offsetInCharacters() ? caretMaxOffset(node) : (int)node->childNodeCount())) {
-        es.throwDOMException(IndexSizeError);
+    if (offset < 0) {
+        es.throwDOMException(IndexSizeError, "Failed to execute 'extend' on a 'Selection' object: " + String::number(offset) + " is not a valid offset.");
+        return;
+    }
+    if (offset > (node->offsetInCharacters() ? caretMaxOffset(node) : (int)node->childNodeCount())) {
+        es.throwDOMException(IndexSizeError, "Failed to execute 'extend' on a 'Selection' object: " + String::number(offset) + " is larger than the given node's length.");
         return;
     }
 
@@ -361,7 +370,7 @@ PassRefPtr<Range> DOMSelection::getRangeAt(int index, ExceptionState& es)
         return 0;
 
     if (index < 0 || index >= rangeCount()) {
-        es.throwDOMException(IndexSizeError);
+        es.throwDOMException(IndexSizeError, "Failed to execute 'getRangeAt' on a 'Selection' object: " + String::number(index) + " is not a valid index.");
         return 0;
     }