[psteinroe]

Stacked on #917.

Comments written before a keyword that has no AST node of its own (ELSE, THEN, END, GRANT's ON/TO/FROM) moved past the keyword, sometimes into another branch or clause. The output was stable on reformat, so nothing flagged it, but the comment no longer sat where it was written. Finding P17 of the release review.

select case -- why
when a then 'x' /* inline */ else 'y' end from t;
-- before
select
  case
    when a then 'x'
    else /* inline */ 'y' -- why
  end
from
  t;
-- after
select
  case
    -- why
    when a then 'x' /* inline */
    else 'y'
  end
from
  t;

select case when a /* cond */ then 1 else 2 /* last */ end from t;
-- before
select case when a then /* cond */ 1 else 2 end from /* last */ t;
-- after
select case when a /* cond */ then 1 else 2 /* last */ end from t;

grant select -- c
on t to u;
-- before
grant select
  on table -- c
  t
  to u;
-- after
grant select -- c
  on table t
  to u;

Why they moved

Comments are attached to AST nodes by source position, and a comment that leads goes to the next node: a block comment, an own-line comment, or a comment after a clause keyword. For 'x' /* inline */ else 'y' the next node is 'y', so the comment came out after else. A comment right after case didn't count as following a clause keyword, so it trailed the whole CASE and came out after the last branch. A comment before end led the next node after the CASE, in the FROM clause.

What changed

• When the token after a comment is a keyword that no node starts at, the comment remembers that keyword (before_keyword). A parent that writes such a keyword before a child can take the comments written before it, with emit_comments_before_keyword, and emit them before the keyword. They are emitted like the trailing comments of the previous node, so an own-line comment keeps its own line. Only comments recorded for that exact keyword are taken. A parent that doesn't call it keeps today's placement, so nothing else moves.
• CASE takes them before ELSE and THEN. GRANT/REVOKE takes them before ON and TO/FROM, and GRANT role before TO/FROM.
• A comment before END stays with the last branch: it trails the previous node instead of leading the next one, because nothing inside the CASE follows END.
• CASE counts as a clause keyword, so a line comment right after it goes before the first WHEN.
• The renderer collapses two spaces in a row inside a group that stays on one line, as it already did for broken groups. The comment emission otherwise gave a /* cond */ then.

Tests

• New tests in comment_layout.rs cover a comment before ELSE, THEN and END, after CASE, and before GRANT's ON and TO, in fit and expanded layout, each formatted twice to check idempotence.
• Two unit tests in comments.rs cover the attachment.
• No snapshot changes: the snapshot harness renders without comments.
• The option matrix from test(pretty_print): fuzz the option matrix in CI #912 passes over the fixtures and the regression suite.

Not covered

Other keyword-only positions (ON in a join, AS before an alias, FROM in a SELECT, ...) keep the old placement. They can opt in the same way when needed.