Add keyword to Objective-C using Clang

Question

How would I go about adding a relatively trivial keyword to Objective-C using the Clang compiler? For example, adding a literal @yes which maps to [NSNumber numberWithBool:YES].

I have looked at the (excellent) source code for Clang and believe that most of the work I would need to do is in lib/Rewrite/RewriteObjC.cpp. There is the method RewriteObjC::RewriteObjCStringLiteral (see previous link) which does a similar job for literal NSString * instances.

I ask this question as Clang is very modular and I'm not sure which .td (see tablegen) files, .h files and AST visitor passes I would need to modify to achieve my goal.

Answer 1

If I understand the clang's code correctly (I'm still learning, so take caution), I think the starting point for this type of addition would be in Parser::ParseObjCAtExpression within clang/lib/Parse/ParseObjc.cpp.

One thing to note is that the Parser class is implemented in several files (seemingly separated by input language), but is declared entirely in clang/include/Parser.h.

Parser has many methods following the pattern of ParseObjCAt, e.g., ParseObjCAtExpression ParseObjCAtStatement ParseObjCAtDirectives etc..

Specifically, line 1779 of ParseObjc.cpp appears to be where the parser detects an Objective-C string literal in the form of @"foo". However, it also calls ParsePostfixExpressionSuffix which I don't fully understand yet. I haven't figured out how it knows to parse a string literal (vs. an @synchronize, for example).

ExprResult Parser::ParseObjCAtExpression(SourceLocation AtLoc) {
...
        return ParsePostfixExpressionSuffix(ParseObjCStringLiteral(AtLoc));
...
}

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