lean4-htt/tests/lean/run/diagnostics.lean
Leonardo de Moura ab26eaf647
feat: enable implicit argument transparency bump (part 2) (#12572)
This PR is part 2 of the `implicit_reducible` refactoring (part 1:
#12567).

**Background.** When Lean checks definitional equality of function
applications
`f a₁ ... aₙ =?= f b₁ ... bₙ`, it compares arguments `aᵢ =?= bᵢ` at a
transparency level determined by the binder type. Previously, only
instance-implicit (`[C]`) arguments received a transparency bump to
`.instances`. With `backward.isDefEq.implicitBump` enabled, ALL implicit
arguments (`{x}`, `⦃x⦄`, and `[x]`) are bumped to `.instances`, so that
definitions marked `[implicit_reducible]` unfold when comparing implicit
arguments. This is important because implicit arguments often carry type
information (e.g., `P (i + 0)` vs `P i`) where the mismatch is in
non-proof positions (Sort arguments to `cast`) — proof irrelevance does
not
help here, so the relevant definitions must actually unfold.

**`[implicit_reducible]`** (renamed from `[instance_reducible]` in part
1) marks
definitions that should unfold at `TransparencyMode.instances` — between
`[reducible]` (unfolds at `.reducible` and above) and the default
`[semireducible]` (unfolds only at `.default` and above). This is the
right
level for core arithmetic operations that appear in type indices.

## Changes

- **Enable `backward.isDefEq.implicitBump` by default** and set it in
  `stage0/src/stdlib_flags.h` so stage0 also compiles with it
- **Mark `Nat.add`, `Nat.mul`, `Nat.sub`, `Array.size` as
`[implicit_reducible]`**
so they unfold when comparing implicit arguments at `.instances`
transparency
- **Remove redundant unification hints** (`n + 0 =?= n`, `n - 0 =?= n`,
  `n * 0 =?= 0`) that are now handled by `[implicit_reducible]`
- **Rename all remaining `[instance_reducible]` attribute usages** to
`[implicit_reducible]` across the codebase (the old name remains as an
alias)
- **Remove 28 `set_option backward.isDefEq.respectTransparency false
in`**
  workarounds that are no longer needed

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-20 03:28:48 +00:00

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opaque q : Nat → Nat
def f (x : Nat) : Nat :=
match x with
| 0 => 1
| x+1 => q (f x)
theorem f_eq : f (x + 1) = q (f x) := rfl
/--
trace: [diag] Diagnostics
[reduction] unfolded declarations (max: 15, num: 3):
[reduction] Nat.rec ↦ 15
[reduction] Add.add ↦ 10
[reduction] HAdd.hAdd ↦ 10
[reduction] unfolded reducible declarations (max: 15, num: 1):
[reduction] Nat.casesOn ↦ 15
use `set_option diagnostics.threshold <num>` to control threshold for reporting counters
-/
#guard_msgs in
example : f (x + 5) = q (q (q (q (q (f x))))) :=
set_option diagnostics.threshold 5 in
set_option diagnostics true in
rfl
/--
trace: [diag] Diagnostics
[reduction] unfolded declarations (max: 15, num: 3):
[reduction] Nat.rec ↦ 15
[reduction] Add.add ↦ 10
[reduction] HAdd.hAdd ↦ 10
[reduction] unfolded reducible declarations (max: 15, num: 1):
[reduction] Nat.casesOn ↦ 15
use `set_option diagnostics.threshold <num>` to control threshold for reporting counters
-/
#guard_msgs in
example : f (x + 5) = q (q (q (q (q (f x))))) := by
set_option diagnostics.threshold 5 in
set_option diagnostics true in
rfl