Description:
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Copying a file into itself causes the source file to be truncate to 0 bytes.

copy("test", "test"); // test.txt -> 0

You can't avoid this problem just by comparing the filenames, since one could be a symlink pointing to the other. The following would destroy test1 if test2 is a link to test1:

copy("test1", "test2");



Reproduce code:
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copy("test", "test");


Expected result:
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Nothing happens or a file open error.

Actual result:
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Contents in source file is lost.