[LLVMbugs] [Bug 14036] New: declval/decltype -- incorrect deduction of return type for std::bind

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=14036

             Bug #: 14036
           Summary: declval/decltype -- incorrect deduction of return type
                    for std::bind
           Product: clang
           Version: trunk
          Platform: Macintosh
        OS/Version: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: randy.thiemann at student.uhasselt.be
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Test case:
#include <functional>
#include <type_traits>
#include <random>

typedef decltype(std::bind(
            std::declval<std::uniform_int_distribution<int>>(), 
            std::declval<std::default_random_engine>())) func;

func randInt(int max) {
    std::default_random_engine engine;
    std::uniform_int_distribution<int> dist(0, max);
    return std::bind(dist, engine);
}

int main() {
    int i = randInt(9)();
}


Expected behaviour:
The typedef "func" matches the return type of the function randInt.


Actual behaviour:
clang does not build the test case:

test.cpp:12:12: error: no viable conversion from
      '__bind<std::__1::uniform_int_distribution<int> &,
      std::__1::linear_congruential_engine<unsigned int, 48271, 0, 2147483647>
      &>' to 'func' (aka '__bind<std::__1::uniform_int_distribution<int>,
      std::__1::linear_congruential_engine<unsigned int, 48271, 0,
      2147483647>>')
    return std::bind(dist, engine);
           ^~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib/c++/v1/functional:1682:5: note: candidate constructor not
      viable: no known conversion from
      '__bind<std::__1::uniform_int_distribution<int> &,
      std::__1::linear_congruential_engine<unsigned int, 48271, 0, 2147483647>
      &>' to 'const std::__1::__bind<std::__1::uniform_int_distribution<int>,
      std::__1::linear_congruential_engine<unsigned int, 48271, 0, 2147483647>>
      &' for 1st argument;
    __bind(const __bind& __b)
    ^
/usr/bin/../lib/c++/v1/functional:1695:5: note: candidate constructor not
      viable: no known conversion from
      '__bind<std::__1::uniform_int_distribution<int> &,
      std::__1::linear_congruential_engine<unsigned int, 48271, 0, 2147483647>
      &>' to 'std::__1::__bind<std::__1::uniform_int_distribution<int>,
      std::__1::linear_congruential_engine<unsigned int, 48271, 0, 2147483647>>
      &&' for 1st argument;
    __bind(__bind&& __b)
    ^
1 error generated.


Extra notes:
Build tested on clang 3.1svn on OS X 10.8.2, using flags: -std=c++11
-stdlib=libc++.
Also tested on gcc 4.7.2 on OS X 10.8.2, using flags -std=c++11. It builds
using this configuration.

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