[LLVMbugs] [Bug 20454] New: Missing warning for implicit cast from qualified id to class that shares a conforming protocol

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20454

            Bug ID: 20454
           Summary: Missing warning for implicit cast from qualified id to
                    class that shares a conforming protocol
           Product: clang
           Version: trunk
          Hardware: Macintosh
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: yiding at fb.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 12828
  --> http://llvm.org/bugs/attachment.cgi?id=12828&action=edit
repro.m

Implicit casting from qualified ID that conforms to a protocol to a class that
conforms to a protocol should give a warning but does not, even with -Wall.

This allows for unsafe casts to pass by with no warning, which allows for
impossible function calls or ivar accesses to happen (demonstrated in attached
repro case) with no warnings.

The code seems to allow this explicitly and there are tests which assert that
this should be allowed. As this seems pretty broken I don't see why it ought to
be.

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