[LLVMbugs] [Bug 23856] New: Generic lambda init-captures can't be captured again

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23856

            Bug ID: 23856
           Summary: Generic lambda init-captures can't be captured again
           Product: clang
           Version: 3.6
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++14
          Assignee: unassignedclangbugs at nondot.org
          Reporter: jvp4846 at g.rit.edu
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 14476
  --> https://llvm.org/bugs/attachment.cgi?id=14476&action=edit
Test case

Sorry for the confusing bug title; I couldn't come up with a better description
that wasn't incredibly verbose. Anyway...

If you use an init-capture with a generic lambda, and then in turn capture that
capture in another lambda, the compiler fails, thinking that the variable used
in the init-capture's *initializer* is being *captured*. See the test file,
which produces these errors on clang 3.4, 3.5, and 3.6 (full versions below):

--------------------
$ clang++-3.4 -std=c++1y test.cpp
test.cpp:10:17: error: variable 'i' cannot be implicitly captured in a lambda
      with no capture-default specified
  auto f = [cap=i*2](auto) {
                ^
test.cpp:5:3: note: in instantiation of function template specialization
      'main()::<anonymous class>::operator()<int>' requested here
  f(1); // (1)
  ^
test.cpp:13:3: note: in instantiation of function template specialization
      'metafunc<<lambda at test.cpp:10:12> >' requested here
  metafunc(f);
  ^
test.cpp:9:7: note: 'i' declared here
  int i = 1;
      ^
test.cpp:10:12: note: lambda expression begins here
  auto f = [cap=i*2](auto) {
           ^
1 error generated.
--------------------

The full versions of clang are:

  Ubuntu clang version 3.4.2- (branches/release_34) (based on LLVM 3.4.2)
  Target: x86_64-pc-linux-gnu
  Thread model: posix

  Debian clang version 3.5.2-svn232162-1~exp1 (branches/release_35) (based on
LLVM 3.5.2)
  Target: x86_64-pc-linux-gnu
  Thread model: posix

  Ubuntu clang version 3.6.0-2ubuntu1~trusty1 (tags/RELEASE_360/final) (based
on LLVM 3.6.0)
  Target: x86_64-pc-linux-gnu
  Thread model: posix

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