[m-rev.] for post-commit review: unused interface imports

[Peter Wang]

On Mon, 09 Aug 2021 13:44:36 +1000 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> For review by anyone.
> 
> Zoltan.

> Fix a bug in the unused import computation.
> 
> compiler/unused_imports.m:
>     The bug was that if a procedure is exported, then the code considered
>     that any module mentioned in the type of *any* its variables was used
>     in the interface, when in fact only the modules mention in the types
>     of its *arguments* are used in the interface; the rest are used *only*
>     in the implementation.
> 
>     Improve the debugging infrastructure.
> 
> NEWS:
>     Announce the change in the behavior of --warn-unused-imports.
> 
> compiler/type_util.m:
>     If a type_ctor has an unqualified sym_name, return "builtin" as its
>     module name, since
> 
>     - after typechecking, all type_ctors will be module qualified, with
>       the only exceptions being the type_ctors of builtin types; and
>     - before typechecking, no type_ctors will be module qualified beyond
>       whatever qualification may have been written down explicitly
>       by the programmer, which makes calling the affected functions futile.
> 

> diff --git a/NEWS b/NEWS
> index ac7c103b0..fc6de6e26 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -487,6 +487,10 @@ Changes to the Mercury compiler
>    keep `opt1` enabled even if `opt1` is not normally enabled at optimization
>    level `N`.
>  
> +* Due to a bugx fix, the --warn-unused-imports is now stricter in warning

Typo: bugx

> +  about modules that are imported in the interface section but are not used
> +  in the interface section.
> +
>  Portability improvements
>  ------------------------
>  

> diff --git a/compiler/type_util.m b/compiler/type_util.m
> index 22102d991..c42da43ed 100644
> --- a/compiler/type_util.m
> +++ b/compiler/type_util.m
> @@ -462,7 +462,8 @@
>  %-----------------------------------------------------------------------------%
>  
>  type_ctor_module(type_ctor(TypeSymName, _Arity)) = ModuleName :-
> -    sym_name_get_module_name_default(TypeSymName, unqualified(""), ModuleName).
> +    sym_name_get_module_name_default(TypeSymName,
> +        unqualified("builtin"), ModuleName).
>  
>  type_ctor_name(type_ctor(TypeSymName, _Arity)) =
>      unqualify_name(TypeSymName).
> @@ -471,8 +472,8 @@ type_ctor_arity(type_ctor(_TypeSymName, Arity)) = Arity.
>  
>  type_ctor_module_name_arity(type_ctor(TypeSymName, Arity), ModuleName, Name,
>          Arity) :-
> -    sym_name_get_module_name_default_name(TypeSymName, unqualified(""),
> -        ModuleName, Name).
> +    sym_name_get_module_name_default_name(TypeSymName,
> +        unqualified("builtin"), ModuleName, Name).
>  

Consider adding the explanation from the log message
regarding why these return "builtin" as a comment.

The rest looks fine.

Peter