[llvm-bugs] [Bug 38542] New: llvm-ar 'Replace' option adds duplicate files to thin archives

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38542

            Bug ID: 38542
           Summary: llvm-ar 'Replace' option adds duplicate files to thin
                    archives
           Product: tools
           Version: 6.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: llvm-ar
          Assignee: unassignedbugs at nondot.org
          Reporter: wdelgenio at ocient.com
                CC: llvm-bugs at lists.llvm.org

When creating thin archives, the 'Replace' option is buggy and will allow for
multiple copies of the same object file within the archive iff the object file
is not in the current directory.

Steps to reproduce:
mkdir foo
clang -c -x c /dev/null -o foo/test.o
llvm-ar Trcs test.a foo/test.o
llvm-ar Trcs test.a foo/test.o
llvm-ar t test.a

Output:
/foo/test.o
/foo/test.o

The bug appears to be in computerInsertAction() in llvm-ar.cpp:

  auto MI = find_if(Members, [Name](StringRef Path) {
    return Name == sys::path::filename(Path);
  });

The objects files are stored with the full path in the thin archive format, but
sys::path::filename will throw out the path, making the find_if function fail
every time unless the object file is in the current directory.  Ie in the
example above Name = "/foo/test.o" and sys::path::filename(Path) = "test.o".

I think the fix is to check if it's a thin archive, and if so, compare Name and
Path without the call to filename().

Will that work?

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