[m-rev.] for post-commit review: fix crash while adding pragmas

[Julien Fischer]

On Sun, 19 Dec 2021, Zoltan Somogyi wrote:

> Fix compiler abort adding pragmas for unknown procs.
> 
> compiler/add_pragma.m:
>     The code that added gen_pragmas (pragmas that are generated
>     *only* by the compiler, and which hold the analysis results)
>     to the HLDS checked whether the *predicate* named by the pragma
>     existed, and was prepared for the case where it did not.
>     However, it was NOT prepared for the case where the predicate
>     did exist, but the *procedure* whose mode number the pragma also named
>     did not exist. It called module_info_pred_proc_info, which did a map.lookup
>     in the predicate's procedure table, which crashed the compiler
>     when the lookup failed.
>
>     The code that puts these pragmas into .opt files does not check
>     whether the pragma is for a predicate whose declaration will be visible
>     to the readers of the .opt file, either by being contained in the
>     module's .int file (for exported predicates) or in the .opt file itself
>     (for nonexported predicates). Fixing that will be next.
>
>     To help with that fix, change how we handle pragmas whose target
>     predicate/procedure is not uniquely determined, i.e. either unknown
>     or ambiguous. Before, we always ignored the error. Now, we still do that
>     by default, but a developmer can now specify a new option
>     which will cause add_pragma.m to generate an informational message
>     for each such pragma.
> 
> compiler/options.m:
>     Add the new option, --inform-ignored-pragma-errors.
> 
> doc/user_guide.texi:
>     Document the new option, as well as an old one whose documentation
>     was missing.

That's fine.

Julien.