rst: invalid use of admonition silently removes line

[timotheecour]

/cc @a-mr
just found this in docs https://nim-lang.github.io/Nim/iterators.html for fieldPairs, which were missing a line This really transforms the 'for' and unrolls the loop. The because docs used .. warning::: instead of .. warning::

Example

iterator fieldPairs2*[T: tuple|object](x: T): tuple[key: string, val: RootObj] =
  ## Iterates over every field of `x` returning their name and value.
  ##
  ## .. warning::: This really transforms the 'for' and unrolls the loop. The
  ##   current implementation also has a bug that affects symbol binding in the
  ##   loop body.

Current Output

please check whether the problem still exists in git head before posting,
see rebuilding the compiler.

Hola mundo!

Expected Output

if it's illegal in RST, give a CT error (simplest) or warning when running nim doc
if it's legal in RST, give a warning and probably render the skipped line as text

Additional Information

1.5.1 70a3031

[a-mr]

Unfortunately .. syntax is reused for comments in rst, so it's legal.

But I agree that a warning should be given. Especially easy is to input single : after a directive name instead of ::.