Re: [patch 2/7] LICENSES: Add the GPL 2.0 license

[Jonas Oberg]

Hi Thomas,

I do appreciate your work on this, it's a welcome addition!

> +SPDX-License-Identifier: GPL-2.0  // GPLv2 only
> +SPDX-License-Identifier: GPL-2.0+ // GPLv2 or later

I am concerned about this though, as the SPDX-License-Identifier is well
known to refer to the license of the document in which it appears, and
it would be beneficial to avoid a situation where a tool reading this
make the assumption the license text itself it under a particular
license. Essentially, let's avoid overloading if we can.

>From my reading, there are two intentions with the above reading:

 1) To give usage guidelines and signal that for any source file, adding
    this exact line would be a valid license identifier, and
 2) To make the license identifiers computer understandable such that
    tools can be updated to validate whether source code includes a
    license identifier which corresponds to one of the licenses in
    LICENSES/

I'd propose to not try to do both at the same time and would propose
a 'Valid-License-Identifier' tag to meet your second criteria, and
a 'Usage-Guidance' tag to meet your first one. The header would then
be:

Valid-License-Identifier: GPL-2.0
Valid-License-Identifier: GPL-2.0+
Usage-Guidance:
 To use this license in source code, you can use either of the following tags
 and values:
 .
 SPDX-License-Identifier: GPL-2.0   // For GPLv2 only
 SPDX-License-Identifier: GPL-2.0+  // For GPLv2 or any later version


Best,

-- 
Jonas Öberg
Executive Director

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