[cfe-dev] Returning original parsing state after parsing arbitrary tokens

[ja_comp]

Eli Friedman wrote
> On Tue, Oct 23, 2012 at 3:02 AM, Eli Friedman <

> eli.friedman@

> > wrote:

>> It's impossible to completely save/restore the state of semantic
>> analysis short of using fork() or equivalent.

> This is a slight exaggeration; that said, parsing a statement in
> thegeneral case can change essentially arbitrary pieces of the AST andthe
> lookup data-structures in Sema, particularly in C++ when
> templateinstantiation is involved.  Even in C there are bits stored in the
> ASTlike whether a declaration is used which can't be easilysaved/restored. 

The sub-goal is to parse the parameters of function-like macros to produce
StmtResults without altering the normal parsing. While all macro parameters
may not be well formed, most will likely produce valid results after calling
ParseStatement.
The goal is to facilitate source-to-source translation by walking the AST.
Maintaining the original parameters for function-like macros is desirable in
this task.
(I realize that having a valid StmtResult is only half of the equation to
determining if the parameter makes sense to be parsed in isolation. The next
task is to expand the macro to a canonical form using the obtained
StmtResult, and compare against a canonical form of the "normally parsed"
already expanded macro)
My code to parse macro parameters works on simple cases, but not when
including certain headers because of parsing state changes.
Would you recommend I resort to fork() and messaging, or is there a more
elegant solution to keep the parsing state pristine?




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