feat: abstract tactic

[fpvandoorn]

This can be used to hide long proofs in the statement of a theorem behind an auxiliary lemma.

Co-authored-by: Sven Manthe [email protected]

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[github-actions]

PR summary 52e3c47a35

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.Tactic	1
Mathlib.Tactic.Abstract (new file)	21

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Declarations diff

+ foo

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[JovanGerb]

It would be nicer if the generated name was more robust. For example you could use mkAuxName ((← getDeclName?).get! ++ `abstract) 1.

Also the get! looks a bit dodgy, but it might be fine.

[JovanGerb]

Can you add a test showing that when tacs doesn't close the goal, abstract tacs gives the same error message as tacs?

[fpvandoorn]

We want to support multiple abstract calls in the same lemma statement. I guess we could use the smallest number where the lemma doesn't exist yet?

[JovanGerb]

Yes, mkAuxName keeps incrementing the given number (1) until it gives a name that isn't taken yet.