[m-rev.] for review: disable_warnings scope

[Zoltan Somogyi]

On Wed, 11 Jan 2017 14:13:57 +1100 (AEDT), "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> Instead, I think I can implement the disabling of warnings generated by
> ml_tailcalls.m by
> 
> - adding a field to the state of the HLDS-to-MLDS code generator that gives
>    a list of the warnings disabled by any disable_warnings scopes surrounding
>    the goal it is currently translating,
> - when it translates a call, marking the ml_stmt_call it generates with the
>    disabled warnings applicable to that calls (currently only the warning
>    we are talking about now, but later possible others as well),
> - having ml_tailcall.m not generate its warning if the call's markings
>    say the warning should be disabled.
> 
> This gets information about suppressing the warning from the HLDS
> to the MLDS without having to introduce a scope construct to the MLDS.
> 
> Alternatively, instead of marking calls at code generation time,
> we could have an earlier pass (maybe simplification) attach a goal feature
> to HLDS call goals, and the HLDS-to-MLDS code generator could mark
> ml_stmt_calls based on the absence or presence of this feature.
> The difference would be in whether we mark calls that are (a) in the scope
> when the code generator sees it, or (b) in the scope in the source that
> the programmer sees. The difference is in code transformations that can move
> code in or out of scopes.

The attached diff implements option (a), as the above email and the reply
to it agreed. It fixes the failure of the require_tailrec_1 test case in MLDS grades.

Once this is installed, we can publically document the ability to disable
warnings about non-tail recursive calls.

For review by anyone.

Zoltan.

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