slow typeclass synthesis: takes 19000 heartbeats to fail on `AddMonoidHomClass (AddGroupSeminorm ℂ) ℂ ℝ`

[Kim Morrison]

live.lean-lang.org

import Mathlib

open Complex Filter Bornology

/--
error: failed to synthesize
  AddMonoidHomClass (AddGroupSeminorm ℂ) ℂ ℝ
(deterministic) timeout at 'typeclass', maximum number of heartbeats (19000) has been reached (use 'set_option synthInstance.maxHeartbeats <num>' to set the limit)
-/
#guard_msgs in
set_option synthInstance.maxHeartbeats 19000 in
#synth AddMonoidHomClass (AddGroupSeminorm ℂ) ℂ ℝ

-- This then results in a near failure (or failure on nightly-testing) of the simpNF linter on
-- `Complex.comap_exp_cobounded` and `Complex.map_exp_comap_re_atTop`:

/--
error: failed to synthesize
  AddMonoidHomClass (AddGroupSeminorm ℂ) ℂ ℝ
(deterministic) timeout at 'typeclass', maximum number of heartbeats (19000) has been reached (use 'set_option synthInstance.maxHeartbeats <num>' to set the limit)
-/
#guard_msgs in
set_option synthInstance.maxHeartbeats 19000 in
example : comap exp (cobounded ℂ) = comap re atTop := by simp

Output of

set_option trace.Meta.synthInstance true in
#synth AddMonoidHomClass (AddGroupSeminorm ℂ) ℂ ℝ 

[Matthew Robert Ballard]

Also fixed by leanprover/lean4#4085

[Johan Commelin]

I confirm that this is fixed:

import Mathlib

/-!
# Test against slow typeclass synthesis

This file tests against regression in typeclass synthesis speed.

See https://github.com/leanprover-community/mathlib4/issues/12226
for the initial issue, that was fixed by
https://github.com/leanprover/lean4/pull/4085
-/

open Complex Filter Bornology

/--
error: failed to synthesize
  AddMonoidHomClass (AddGroupSeminorm ℂ) ℂ ℝ
-/
#guard_msgs in
set_option synthInstance.maxHeartbeats 3000 in
#synth AddMonoidHomClass (AddGroupSeminorm ℂ) ℂ ℝ

-- This then results in a near failure (or failure on nightly-testing) of the simpNF linter on
-- `Complex.comap_exp_cobounded` and `Complex.map_exp_comap_re_atTop`:

set_option synthInstance.maxHeartbeats 3000 in
example : comap exp (cobounded ℂ) = comap re atTop := by simp