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fix: improve error message for initialize with missing Nonempty instance #11919

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Merged
kim-em merged 2 commits into from
Jan 8, 2026
Merged

fix: improve error message for initialize with missing Nonempty instance #11919

kim-em merged 2 commits into from
Jan 8, 2026

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@kim-em kim-em commented Jan 6, 2026

This PR improves the error message when initialize (or opaque) fails to find an Inhabited or Nonempty instance.

Before:

failed to synthesize
  Inhabited Foo

After:

failed to synthesize 'Inhabited' or 'Nonempty' instance for
  Foo

If this type is defined using the 'structure' or 'inductive' command, you can try adding a 'deriving Nonempty' clause to it.

Prompted by https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/initialize.20structure.20with.20IO.2ERef/near/564936030

🤖 Prepared with Claude Code

@kim-em @claude
fix: improve error message for initialize with missing Nonempty i…
f5b1ed2 
…nstance

This PR improves the error message when `initialize` (or `opaque`) fails
to find an `Inhabited` or `Nonempty` instance. Previously, the error was
just "failed to synthesize Inhabited Foo", which didn't hint that
`Nonempty` would also work. The new message explains that both were
tried and suggests adding `deriving Nonempty`.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
@kim-em kim-em added the changelog-language Language features and metaprograms label Jan 6, 2026
@kim-em @claude
chore: update expected output for sanitychecks test
436dc88 
🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
@github-actions github-actions bot added the toolchain-available A toolchain is available for this PR, at leanprover/lean4-pr-releases:pr-release-NNNN label Jan 7, 2026
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leanprover-community-bot commented Jan 7, 2026

Mathlib CI status (docs):

  • ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 11e4e44be070ec99bc734e40f8431fd92725842d --onto 0f866236c7c2e77e8d12ff61d08ef48694a0cbfb. You can force Mathlib CI using the force-mathlib-ci label. (2026-01-07 03:47:11)

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leanprover-bot commented Jan 7, 2026

Reference manual CI status:

  • ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 11e4e44be070ec99bc734e40f8431fd92725842d --onto 0f866236c7c2e77e8d12ff61d08ef48694a0cbfb. You can force reference manual CI using the force-manual-ci label. (2026-01-07 03:47:12)

@kim-em kim-em added this pull request to the merge queue Jan 7, 2026
Merged via the queue into master with commit f7de0c4 Jan 8, 2026
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