leanprover-community/mathlib4

Make `scripts/add_deprecations.sh` support additivised declarations

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#38,550 opened on Apr 26, 2026

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Description

Currently, changing

@[to_additive]
lemma foo_mul ...

to

@[to_additive]
lemma bar_mul ...

then running scripts/add_deprecations.sh creates

@[to_additive]
lemma bar_mul ...

@[deprecated ...] alias foo_mul := bar_mul

It should instead create

@[to_additive]
lemma bar_mul ...

@[deprecated ...] alias foo_mul := bar_mul
@[deprecated ...] alias foo_add := bar_add

Note that

@[to_additive (attr := deprecated ...)] alias foo_mul := bar_mul

doesn't work because deprecated loses track of what the deprecated declaration is an alias of (see #19424).

Contributor guide

Research direction
Investigate the `to additive` attribute and understand how the script currently processes declarations. Trace the logic in `scripts/add deprecations.sh` to modify it to also generate deprecation aliases for additive versions.
Tech stack
shell
Domain
build systemdevops
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
GitShell
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40