[cdt-dev] empty AST macro expansions

[Andrew Eidsness <eclipse@xxxxxxxxxx>]

I'm trying to use the AST to discover whether a specific macro was used 
to create a particular node in the AST.  I'm calling 
IASTNode.getNodeLocations and looking for instances of 
IASTMacroExpansionLocation that reference the target macro.

This works if the macro expands to a real value, but does not work when 
the expansion is to nothing.  E.g., expansions of the first macro are 
found, expansions of the second are not:

	#define FOUND     found
	#define NOT_FOUND

The reason for the difference is the implementation of 
LocationCtxContainer.collectLocations.

In both cases, the LocationCtxMacroExpansion is present in the fChildren 
list.  However, in the NOT_FOUND case, the child's fSequenceNumber is 
the same as childEndSequenceNumber (since length is 0).

Approximately:

	if (sequenceNumber < child.fSequenceNumber) {
	// ...
[159]		sequenceNumber= child.fSequenceNumber;
	}

	// ...
[164]	if (sequenceNumber < childEndSequenceNumber) {
		child.collectLocations( // ...

The loop's counter, sequenceNumber, is advanced (on line 159), which is 
before the check to see if the child is within the target range (on line 
164).

The questions that I have are:

	1) Is there a better way to do what I want?  The expansion that I'm 
looking for is stored in the node's fChildren list, maybe there is a 
different way to access it?

	2) Is this a bug or a feature?  :-)  Is there other code that depends 
on empty expansions being removed from the result?

If it is a bug, then I could submit a patch to fix it.  My first ideas are:
	a) empty expansions should be given a sequenceLength of 1 when the 
LocationCtxMacroExpansion is created, or

	b) the sequenceNumber counter should not be incremented until the child 
is fully processed.

-Andrew