Fix ICE when parsing frontmatter without newline

[chenyukang]

Fixes #151882

we can not add a normal test case for it:

• no newline at the end of file, we can bypass this with change test file name with ignore-tidy
• multiple errors in stderr, this conflicts with the previous bypass, seems we can not add multiple error annotations in one line

anyway, I added a run-make test for it.

[rustbot]

r? @mati865

rustbot has assigned @mati865.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[chenyukang]

======== tests/rustdoc-gui/globals.goml ========

[ERROR] line 14: Error: The window properties still all match: for command wait-for-window-property-false: {"searchIndex": null}
at file:///checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc-gui/doc/test_docs/index.html?search=Foo

======== tests/rustdoc-gui/search-result-display.goml ========

[WARNING] line 39: Delta is 0 for "x", maybe try to use compare-elements-position instead?

flaky test

[rustbot]

Some changes occurred in GUI tests.

cc @GuillaumeGomez

[chenyukang]

seems PR not working?
#151856
@GuillaumeGomez

[Kivooeo]

would be

- let last_line_start = real_s.rfind('\n').map_or(0, |i| i + 1);
+ let last_line_start = real_s.rfind('\n').map_or(line_end, |i| i + 1);

enough to fix it?

[chenyukang]

would be

- let last_line_start = real_s.rfind('\n').map_or(0, |i| i + 1);
+ let last_line_start = real_s.rfind('\n').map_or(line_end, |i| i + 1);

enough to fix it?

yeah, simpler.

[Kivooeo]

r=me with ci green

[Kivooeo]

@bors r+ rollup

[rust-bors]

📌 Commit dc48704 has been approved by Kivooeo

It is now in the queue for this repository.