Summary
--
This is the other commit I wanted to spin off from #19415, currently
stacked on #19644.
This PR suppresses blank snippets for empty ranges at the very beginning
of a file, and for empty ranges in non-existent files. Ruff includes
empty ranges for IO errors, for example.
f4e93b6335/crates/ruff_linter/src/message/text.rs (L100-L110)
The diagnostics now look like this (new snapshot test):
```
error[test-diagnostic]: main diagnostic message
--> example.py:1:1
```
Instead of [^*]
```
error[test-diagnostic]: main diagnostic message
--> example.py:1:1
|
|
```
Test Plan
--
A new `ruff_db` test showing the expected output format
[^*]: This doesn't correspond precisely to the example in the PR because
of some details of the diagnostic builder helper methods in `ruff_db`,
but you can see another example in the current version of the summary in
#19415.
b324ae1be3