[llvm-bugs] [Bug 26217] New: cannot inherit priority_queue's constructors due to enable_if in some cases.

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26217

            Bug ID: 26217
           Summary: cannot inherit priority_queue's constructors due to
                    enable_if in some cases.
           Product: libc++
           Version: 3.7
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: koolcoy at gmail.com
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com
    Classification: Unclassified

The following code won't compile against libc++ with clang++-3.7 (it compiles
as expected against libstdc++ with clang++-3.7 or g++-5). If data member Foo::f
is moved to a function local scope or to global scope, the code also compiles

#include <queue>

template<typename T, typename Container = std::vector<T>,
        typename Compare = std::less<T>>
class PriorityQueue : public std::priority_queue<T, Container, Compare> {
    using Parent = std::priority_queue<T, Container, Compare>;
public:
    using std::priority_queue<T, Container, Compare>::priority_queue;

    void clear() {
        this->c.clear();
    }
};

struct Foo {
    struct Node {
        int distance;
    };

    struct Compare {
        bool operator () (Node* a, Node* b) const {
            return a->distance < b->distance;
        }
    };

    PriorityQueue<Node*, std::vector<Node*>, Compare> f;
};

void f() {
    Foo x;
};

error message:

In file included from t.cpp:1:
/opt/local/libexec/llvm-3.7/bin/../include/c++/v1/queue:450:43: error: no type
      named 'type' in 'std::__1::enable_if<false, void>'; 'enable_if' cannot be
      used to disable this declaration
                       typename enable_if<uses_allocator<container_type,
                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
t.cpp:8:52: note: in instantiation of member function
      'std::__1::priority_queue<Foo::Node *, std::__1::vector<Foo::Node *,
      std::__1::allocator<Foo::Node *> >, Foo::Compare>::priority_queue'
      requested here
        using std::priority_queue<T, Container, Compare>::priority_queue;
                                                          ^
t.cpp:5:7: note: while substituting deduced template arguments into function
      template 'PriorityQueue' [with _Alloc = PriorityQueue<Foo::Node *,
      std::__1::vector<Foo::Node *, std::__1::allocator<Foo::Node *> >,
      Foo::Compare>]
class PriorityQueue : public std::priority_queue<T, Container, Compare> {
      ^
In file included from t.cpp:1:
/opt/local/libexec/llvm-3.7/bin/../include/c++/v1/queue:450:43: error: no type
      named 'type' in 'std::__1::enable_if<false, void>'; 'enable_if' cannot be
      used to disable this declaration
                       typename enable_if<uses_allocator<container_type,
                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 errors generated.

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