[cfe-dev] How to debug an AST matcher

Gábor Márton via cfe-dev cfe-dev at lists.llvm.org
Tue Jul 3 03:22:12 PDT 2018

Have you tried the binary "clang-query"? It can save you a few steps,
particularly 3) , 4) and 5).


On Tue, Jul 3, 2018 at 9:10 AM Thomas Patson via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi all,
> I'm a Clang newbie. So, I've been trying to write some basic checkers that
> do AST traversal. Now, one of the difficulties I'm running into is on how
> to debug when my AST matcher doesn't work as expected.
> My current workflow is this:
> 1) `clang -Xclang -ast-dump -fsyntax-only test.cc` and get a sense of how
> the AST tree looks like for code snippets the AST checker is supposed to
> figure out.
> 2) Write the checker.
> 3) Build the checker and fix syntactic plus other rookie errors when the
> compiler points out.
> 4) Run the checker
> 5) Notice that it doesn't work as expected, so stare at the checker. Do 1)
> again and see if I missed anything. If I spot anything, fix the checker and
> restart from 3).
> 6) If ran into 5) and couldn't spot anything in the ast-dump output, then
> go through ASTMatcher.h and try to see if you have a Eureka moment.
> 7) Twiddle my thumbs for a while and then email cfe-dev for help.
> Ideally I want to rely on lldb in this kind of situation, and I suspect
> the answer lies in the Debug Prints and Tricks section (from
> https://clang-analyzer.llvm.org/checker_dev_manual.html). But I was
> hoping someone can perhaps go in more detail than what's in the Debug
> Prints and Tricks section to help a beginner like me. I'll be even more
> specific: Say there's a DeclStmt which has a VarDecl descendant, and I want
> to see if DeclRefExpr contains an IntegerLiteral of value 10 in the
> denominator assuming it's a divide operation. Now assuming that after
> looking at the ast-dump output, you're still not able to figure out what
> might be wrong with your matcher. How would you go about this predicament
> of yours ? I don't want to tell what the specific issue is because I want
> to go through the debugging process myself to figure out the problem with
> my matcher.
> Copy-pasting an old email response for the same type of question should
> suffice.
> Tom
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