Can software released under the Boost software license be relicensed under the Zlib/Libpng License?

Question

I came across a library on GitHub (now Zlib/Libpng licensed) that is a fork of a library that was originally released under the Boost software license.

Is it legitimate/legal to relicense boost software under the zlib license?

I guess the Boost license doesn't explicitly deny nor explicitly allow relicensing as far as I can tell, so I thought it was worth a question.

See: https://github.com/r-lyeh/units

Answer 1

The Boost license specifically states:

The copyright notices in the Software and this entire statement, including the above license grant, this restriction and the following disclaimer, must be included in all copies of the Software, in whole or in part, and all derivative works of the Software, unless such copies or derivative works are solely in the form of machine-executable object code generated by a source language processor.

So no, you can't relicense code under the Boost license.

The project in question is rather confused about its license though; the top of the README still says it's licensed using the Boost license, as does the library's code itself. You could argue that the project as a whole uses the Zlib license, and includes Boost-licensed code, which is valid — but the code in question constitutes the entirety of the project...