More concise error handling about carbon-lang HOT 4 CLOSED

I think the value_or part doesn't work out...

Consider:

      std::optional<const Value*> type = types.Get(ident.Name());
      if (type) {
        return TCExpression(e, *type, types);
      } else {
        FATAL_COMPILATION_ERROR(e->SourceLoc())
            << "could not find `" << ident.Name() << "`";
      }

We probably want lazy evaluation of SourceLoc() and Name(). My best idea for that was to wrap with a macro, but with an eye on maintaining lazy evaluation, the best I reached is:

      const Value* type = types.Get(ident.Name())
                              .value_or(OPTIONAL_FATAL_COMPILATION_ERROR(
                                  const Value*, (e->SourceLoc()),
                                  ("could not find `" << ident.Name() << "`")));
      return TCExpression(e, type, types);

Syntactically, I don't think this ends up being very readable. I think the macros already help a good amount with readability. So my leaning is to consider this sufficiently addressed and close. I'll leave this open a little longer if anybody wants to make suggestions for a better approach.

from carbon-lang.

@geoffromer suggests that we should probably use std::abort rather than std::exit.

from carbon-lang.

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from carbon-lang.

I think the FATAL code partly addresses this, but the point about using value_or is interesting, maybe we can do a little more.

from carbon-lang.