[LLVMbugs] [Bug 12053] New: infinite recursion in decltype crashes compiler

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12053

             Bug #: 12053
           Summary: infinite recursion in decltype crashes compiler
           Product: clang
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++0x
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: seth.cantrell at gmail.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Created attachment 8086
  --> http://llvm.org/bugs/attachment.cgi?id=8086
source, preprocessed source, and build script

Attempting to instantiate the following template causes clang to segfault

template<typename T> auto foo(T t) -> decltype(foo(t)) {}


The printed error

clang: error: unable to execute command: Segmentation fault: 11

preprocessed source, and build script included, as per clang's instructions, as
well as the original source.

The command line I used was simply clang++ -std=c++11 main.cpp


A non-template version of the above does not cause a crash. It simply results
in a compile error because foo is not declared until the opening brace.

auto foo(int t) -> decltype(foo(t)) {}

Also, trying a non-recursive template shows that the name used inside the
decltype is not a dependent name, and so is resolved during the first phase of
two-phase lookup

//int bar(int i) { return 1; }

template<typename T>
auto foo(T t) -> decltype(bar(t))
{
    return bar(t);
}

int bar(double d) { return 2; }

int main() {
    foo(double());
}


If I understand correctly, in the case of the recursive template clang should
be trying to resolve 'foo' inside decltype during the first phase of two-phase
lookup, and this should fail, resulting in a substitution error with a nice
compiler diagnostic.

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