Unexpected token mutual after docstring comment

[ionathanch]

Prerequisites

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• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
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Description

A comment block followed by a mutual block doesn't type check, possibly doesn't parse at all either

Steps to Reproduce

/-- T --/

mutual
inductive T where
end

Expected behavior: Code successfully type checks

Actual behavior: Errors with the following message:

unexpected token 'mutual'; expected '#guard_msgs', 'abbrev', 'add_decl_doc', 'axiom', 'binder_predicate', 'builtin_dsimproc', 'builtin_dsimproc_decl', 'builtin_initialize', 'builtin_simproc', 'builtin_simproc_decl', 'class', 'declare_simp_like_tactic', 'declare_syntax_cat', 'def', 'dsimproc', 'dsimproc_decl', 'elab', 'elab_rules', 'example', 'inductive', 'infix', 'infixl', 'infixr', 'initialize', 'instance', 'macro', 'macro_rules', 'notation', 'opaque', 'postfix', 'prefix', 'simproc', 'simproc_decl', 'structure', 'syntax', 'theorem' or 'unif_hint'

Versions

4.8.0-rc1, as well as Lean nightly at https://live.lean-lang.org/#project=lean-nightly

[nomeata]

Note that you wrote not a normal comment /- but a docstring /--, and docstrings only make sense preceding a declaration. This is probably good, but the error message could be better!

[Kha]

Closing in favor of #3135