[m-rev.] for post-commit review: fix misleading context

[Peter Wang]

On Tue, 03 Aug 2021 13:03:05 +1000 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> Fix a misleading context.
> 
> compiler/state_var.m:
>     When replacing the argument terms !.X or !:X with a reference to
>     the relevant instance of the state var, make the updated form of
>     the argument inherit its context from the original form.
>     The dummy context we used to use would lead to a misleading context
>     in any error message about that argument.
> 
> compiler/superhomogeneous.m:
>     Fix an unrelated problem I came across while tracking down the above bug.
>     The problem was that we used to tell people that lambda expressions
>     had to have the form "<lambda head> :- <lambda body>", even if the
>     malformed lambda expression had "-->" as its top functor, i.e. if it
>     used DCG syntax.
> 
>     Simplify a comment.
> 
> tests/invalid/bad_statevar_bad_context.{m,err_exp}:
>     A new test case for the state var bug above.
> 
> tests/invalid/Mmakefile:
>     Enable the new test case.

That's fine.

Peter