r284777 - Fix off-by-one error in PPCaching.cpp token annotation assertion

[Yung, Douglas via cfe-commits]

Hi Reid,

Just a heads up that the test you added fails if the compiler defaults to a different C++ standard. Our internal version defaults to c++11, and the test fails because the error "expected ';' after top level declarator" is not emitted.

Douglas Yung

> -----Original Message-----
> From: cfe-commits [mailto:cfe-commits-bounces at lists.llvm.org] On Behalf
> Of Reid Kleckner via cfe-commits
> Sent: Thursday, October 20, 2016 13:53
> To: cfe-commits at lists.llvm.org
> Subject: r284777 - Fix off-by-one error in PPCaching.cpp token
> annotation assertion
> 
> Author: rnk
> Date: Thu Oct 20 15:53:20 2016
> New Revision: 284777
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=284777&view=rev
> Log:
> Fix off-by-one error in PPCaching.cpp token annotation assertion
> 
> This assert is intended to defend against backtracking into the middle
> of a sequence of tokens that is being replaced with an annotation, but
> it's OK if we backtrack to the exact position of the start of the
> annotation sequence. Use a <= comparison instead of <.
> 
> Fixes PR25946
> 
> Added:
>     cfe/trunk/test/Parser/backtrack-off-by-one.cpp
> Modified:
>     cfe/trunk/lib/Lex/PPCaching.cpp
> 
> Modified: cfe/trunk/lib/Lex/PPCaching.cpp
> URL: http://llvm.org/viewvc/llvm-
> project/cfe/trunk/lib/Lex/PPCaching.cpp?rev=284777&r1=284776&r2=284777&
> view=diff
> =======================================================================
> =======
> --- cfe/trunk/lib/Lex/PPCaching.cpp (original)
> +++ cfe/trunk/lib/Lex/PPCaching.cpp Thu Oct 20 15:53:20 2016
> @@ -105,7 +105,7 @@ void Preprocessor::AnnotatePreviousCache
>    for (CachedTokensTy::size_type i = CachedLexPos; i != 0; --i) {
>      CachedTokensTy::iterator AnnotBegin = CachedTokens.begin() + i-1;
>      if (AnnotBegin->getLocation() == Tok.getLocation()) {
> -      assert((BacktrackPositions.empty() || BacktrackPositions.back()
> < i) &&
> +      assert((BacktrackPositions.empty() || BacktrackPositions.back()
> + <= i) &&
>               "The backtrack pos points inside the annotated tokens!");
>        // Replace the cached tokens with the single annotation token.
>        if (i < CachedLexPos)
> 
> Added: cfe/trunk/test/Parser/backtrack-off-by-one.cpp
> URL: http://llvm.org/viewvc/llvm-
> project/cfe/trunk/test/Parser/backtrack-off-by-
> one.cpp?rev=284777&view=auto
> =======================================================================
> =======
> --- cfe/trunk/test/Parser/backtrack-off-by-one.cpp (added)
> +++ cfe/trunk/test/Parser/backtrack-off-by-one.cpp Thu Oct 20 15:53:20
> +++ 2016
> @@ -0,0 +1,17 @@
> +// RUN: %clang_cc1 -verify %s
> +
> +// PR25946
> +// We had an off-by-one error in an assertion when annotating A<int>
> +below.  Our // error recovery checks if A<int> is a constructor
> +declarator, and opens a // TentativeParsingAction. Then we attempt to
> +annotate the token at the exact // position that we want to possibly
> backtrack to, and this used to crash.
> +
> +template <typename T> class A {};
> +
> +// expected-error at +1 {{expected '{' after base class list}} template
> +<typename T> class B : T // not ',' or '{'
> +// expected-error at +3 {{C++ requires a type specifier for all
> +declarations}} // expected-error at +2 {{expected ';' after top level
> +declarator}} // expected-error at +1 {{expected ';' after class}} A<int>
> {
> +};
> 
> 
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