Consider changing Span::unknown() and various instances of Span { start: 0, end: 0 } to something else

[webbedspace]

Related problem

No response

Describe the solution you'd like

In a recent PR of mine, I was told not to use Span { start: 0, end: 0 } or Span::unknown() because when displayed in errors, they show garbage arrows pointing to arbitrary code.

However, these are still used in various places in the code, so I'm opening an issue for having them replaced with something else.

"Something else" because I don't have enough familiarity with the codebase to say what this would be. A better Span variant whose error arrows are explicitly not printed, perhaps?

Describe alternatives you've considered

No response

Additional context and details

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[fdncred]

There is Span::test_data() for the occasion when spans don't matter as much, like in tests. Maybe this isn't what you're talking about though since it's the same as the other ones you mentioned.

[sophiajt]

Yeah, I wonder if we can make a lint that allows test_data() in lints but other places requires you to use a real span.

[sophiajt]

I might have a way to clean this up... experimenting now

[sophiajt]

This should help: #7383

There are still other sources of Span::unknown() and Span::new(0, 0), so it's just a start.