Clarify copyright header policy for fork-added and upstream files

[bernalde]

While preparing Pyomo integration work in the SECQUOIA fork, we noticed that copyright headers can become ambiguous when a downstream fork adds new files and modifies existing upstream files.

The concern is that upstream LyoPRONTO does not belong to SECQUOIA, so fork-side PRs should not accidentally imply SECQUOIA ownership over upstream-authored files. Our current working convention in the SECQUOIA fork is:

• Leave existing upstream copyright headers intact for files that already existed upstream.
• Use Copyright (C) 2026, SECQUOIA only for files newly added by SECQUOIA.
• Avoid rewriting untouched upstream files just to normalize headers.

Questions for upstream:

1. What copyright/header convention should contributors follow for files that already existed upstream but are modified by downstream contributors?
2. Should new contributor or organization notices be added as extra header lines, recorded in a central AUTHORS/NOTICE file, or omitted from per-file headers?
3. Should upstream document a repository-wide policy so future PRs apply the same convention consistently?

This came up while working on a stacked set of PRs in the SECQUOIA fork for Pyomo integration. Depending on the preferred policy, several PRs in that stack may need to be updated to keep copyright notices consistent before they are proposed upstream.

[Ickaser]

I have the copyright headers in place because it is recommended to do so for the GPLv3 (see e.g. https://softwareengineering.stackexchange.com/questions/125836/do-you-have-to-include-a-license-notice-with-every-source-file).

Practically speaking, I am open to suggestions on (1) and (2), particularly if you can point to what has been done in practice by other GPLv3 libraries.

(3) probably makes sense to put in the README once we have something.

[bernalde]

Thanks, that makes sense to me. I am not trying to make this heavier than it needs to be, just to avoid implying downstream ownership of upstream-authored files.

My suggested convention is:

1. Keep GPL/license notices in nontrivial source files.
2. For files that already exist in upstream LyoPRONTO, preserve the existing copyright/header.
3. If a downstream contributor adds a substantial copyrightable contribution to an existing file, add a separate copyright line beneath the existing one rather than replacing the upstream notice.
4. For small edits, rely on git history and PR metadata; do not add a new per-file notice just because a fork touched the file.
5. For new files, use the actual copyright holder for that file, e.g. Copyright (C) 2026, SECQUOIA, followed by the same GPL notice style used by the project.
6. Use AUTHORS/CONTRIBUTORS for attribution if desired. I would reserve NOTICE for required third-party notices, not general authorship tracking.

That seems consistent with GNU guidance: copied code should keep its existing notices, copyright/license notices should live near the top of source files, and files with multiple non-assigning contributors can have multiple copyright holders without needing to list every small contributor.

For a more machine-readable future version, REUSE/SPDX is also a reasonable model:

SPDX-FileCopyrightText: ...
SPDX-License-Identifier: GPL-3.0-or-later

But I would not make an SPDX migration a prerequisite here. A short README or CONTRIBUTING section with the rules above would probably be enough.

References:

• GNU GPL how-to: https://www.gnu.org/licenses/gpl-howto.en.html
• GNU copyright notice guidance: https://www.gnu.org/prep/maintain/html_node/Copyright-Notices.html
• GPLv3 section 5: https://www.gnu.org/licenses/gpl-3.0.en.html
• REUSE/SPDX: https://reuse.software/spec/