I've read online that MIT is a permissive licence which allows for the code to be used in propriety products, but the licence texts seems to conflict with that, which I'll quote below:
Copyright (c) <year> <copyright holders>
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
So, it seems according to the licence, derivative works must distribute the licence, and hence give those who receive the software the right to re-distribute the software, which is incompatible with most commercial software licences.
A strict reading would be that only exact copies have to distribute the copyright notice, although this seems a bit silly, as it is trivial to perform a minor modification to avoid an exact copy. Why would the licence bother including the restriction to maintain the copyright notice when that restriction is so easily circumvented?
So if "copy" includes derived works, I can only conclude that any work derived from a MIT licenced work must permit free redistribution, which means it's not really a commercial friendly licence.
The only way around this seems to include the MIT licence files, but then say that these licence files only apply to certain parts to the software, oh and by the way the rights you get to redistribute those parts doesn't really apply practically because they're but of the compiled code now and tightly coupled with bits you can't redistribute (particularly if it wasn't a separate library but just some source code copied into the commercial project).
That seems crazy, and I've also never seen such a notice. But on the other hand, just distributing the MIT licence with the software without these qualifications seems to me that a court might reasonable rule that it applies to the whole software, as you can't break compiled code into one executable into "parts" in any sense.
I'd note also, that if I'm using software
X, which contains code from
XN, to use software
X myself presumably I'd have to include the licences from
XN in distributions of my software.
So for every open source library I use, I'd have to look into its dependencies, find all the licences for it's dependencies, then look into those dependencies, and find all the licences for them, and so on.
This seems like an absolute nightmare, not really "permissive" as the
MIT licence is commonly described. It seems completely impractical to comply with.
Am I correct in this analysis or have I totally missed something?