The source was reduced by Milian to:

class LockableHolder
{
    friend void swap(LockableHolder a, LockableHolder b)
    {
        a = b;
    }
};
 

Execution of clang-parser yields:
 
clang-parser -a /tmp/test.cpp
AST tree successfully generated
ClassDecl (4) | type: "LockableHolder" (105) | display: "LockableHolder" | loc: /tmp/test.cpp@[(1,1),(7,2)] | isDecl
  UnexposedDecl (1) | loc: /tmp/test.cpp@[(3,5),(6,6)] | isDecl
no problems encountered during parsing

Reproducible: Always




This is likely an upstream issue.