[cfe-dev] ASTMatcher for assert()

[Alex Horn]

> [...] Why not write all tools to work on the non-macro-rewritten code?
> (you can get  macros yourself via the PPCallbacks interface).

As far as I understand, PPCallbacks operate on a different level of
abstraction than ASTMatchers. The RefactoringTool I have in mind
rewrites two things: (1) "assert()" macros and (2) control-flow
conditions in "if-then-else", "while" and "for" statements. The
rewriting of both (1) and (2) is now implemented as ASTMatchers.
Unfortunately, (2) does not work correctly unless macros are rewritten
beforehand. To see this, consider "#define compare(a, b) do { if ((a)
< (b)) swap(a, b) } while(0);".

I presumed for now that it does not make sense, generally speaking, to
invoke ASTMatchers from within PPCallbacks because the source code
inside a macro definition may not be well-formed. This is why I was
merely looking for a way to combine ASTMatchers and cc1 drivers.

Best,
Alex

On 6 June 2014 15:13, Manuel Klimek <klimek at google.com> wrote:
> On Fri, Jun 6, 2014 at 4:10 PM, Alex Horn <alex.horn at cs.ox.ac.uk> wrote:
>>
>> Thanks for the effective response. This helped on the right track and
>> I've successfully used SourceManager::getImmediateExpansionRange() to
>> insert BAR and its surrounding parenthesis correctly.
>>
>> As a directly related issue: The proposed technique of using the
>> expansion range does the trick but of course requires that "-cc1
>> -rewrite-macros" is _not_ invoked prior to rewriting "assert()"
>> macros. However, this is problematic when other rewrites in the same
>> RefactoringTool _do_ rely on macros having been rewritten. This poses
>> the question whether these things can coexist in the same
>> RefactoringTool. In particular, is it possible to call the
>> RewriteMacros functionality only after certain matches have completed?
>>
>> To ask the same thing differently, what is the preferred way to
>> compose ASTMatchers and cc1 drivers such as RewriteMacros?
>
>
> I wouldn't combine them. Why not write all tools to work on the
> non-macro-rewritten code? (you can get macros yourself via the PPCallbacks
> interface).
>
>>
>>
>> On 6 June 2014 13:56, Manuel Klimek <klimek at google.com> wrote:
>> > On Tue, Jun 3, 2014 at 5:36 PM, Alex Horn <alex.horn at cs.ox.ac.uk> wrote:
>> >>
>> >> Hello,
>> >>
>> >> I am struggling to replace "assert(c)" macro calls by "BAR(c)" where c
>> >> is some integer expression and BAR is a function.
>> >>
>> >> The problem manifests itself in RefactoringTool::applyAllReplacements
>> >> which returns false, thereby causing the tool to skip replacements.
>> >>
>> >> I am using the following ASTMatcher:
>> >>
>> >> StatementMatcher makeAssertMatcher() {
>> >>   return
>> >>
>> >> callExpr(callee(functionDecl(hasName("__builtin_expect")))).bind("AssertBindId");
>> >> }
>> >>
>> >> Note: callExpr(callee(functionDecl(hasName("assert"))) won't work here
>> >> because assert() is a macro according to the assert.h and cassert
>> >> headers.
>> >>
>> >> Here's an example match using clang-query:
>> >>
>> >> example.cpp:
>> >>
>> >>   #include <assert.h>
>> >>   int main() {
>> >>     assert(false);
>> >>     return 0;
>> >>   }
>> >>
>> >> $ clang-query> match
>> >> callExpr(callee(functionDecl(hasName("__builtin_expect"))))
>> >>
>> >>   Match #1:
>> >>
>> >>   example.cpp:4:3: note: "AssertBindId" binds here
>> >>     assert(false);
>> >>     ^~~~~~~~~~~~~
>> >>   /usr/include/assert.h:93:6: note: expanded from macro 'assert'
>> >>       (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __FILE__,
>> >> __LINE__, #e) : (void)0)
>> >>        ^~~~~~~~~~~~~~~~~~~~~~~~~
>> >>   1 match.
>> >>
>> >> But I cannot find the correct way to rewrite the match; the following
>> >> replacement is skipped (i.e. see line 295 in Refactoring.cpp):
>> >>
>> >>   const CallExpr *E = Result.Nodes.getNodeAs<CallExpr>("AssertBindId");
>> >>   SourceManager &SM = *Result.SourceManager;
>> >>   SourceLocation LocBegin = E->getLocStart();
>> >>   Replace->insert(tooling::Replacement(SM, LocBegin,
>> >>     /* number of letters in assert */ 6, "BAR"));
>> >>
>> >> What is the correct way (if any) to rewrite call expressions of macros
>> >> such as "assert()"?
>> >
>> >
>> > You need to get the expansion location:
>> > SourceLocation ExpLocBegin = SM.getExpansionLoc(LocBegin);
>> > Replace->insert(tooling::Replacement(SM, ExpLocBegin, 6, "BAR"));
>> >
>> > Something like this should do the trick...
>> > Cheers,
>> > /Manuel
>
>