Fix find_width_of_character_at_span bounds check
Commit 0bd96671f0 added bounds checking of our current target byte position to prevent infinite loops. Unfortunately it was comparing the file-relative `target` versus the global `file_start_pos` and `file_end_pos`.
The result is failing to detect multibyte characters unless their file-relative offset fit within their global offset. This causes other parts of the compiler to generate spans pointing to the middle of a
multibyte character which will ultimately panic in `bytepos_to_file_charpos`.
Fix by comparing the `target` to the total file size when moving forward and doing checked subtraction when moving backwards. This should preserve the intent of the bounds check while removing the offset confusion.
cc @davidtwco
Fixes#48508
Commit 0bd96671f0 added bounds checking of our current target byte
position to prevent infinite loops. Unfortunately it was comparing the
file-relative `target` versus the global relative `file_start_pos` and
`file_end_pos`.
The result is failing to detect multibyte characters unless their
file-relative offset fit within their global offset. This causes other
parts of the compiler to generate spans pointing to the middle of a
multibyte character which will ultimately panic in
`bytepos_to_file_charpos`.
Fix by comparing the `target` to the total file size when moving forward
and doing checked subtraction when moving backwards. This should
preserve the intent of the bounds check while removing the offset
confusion.
Fixes#48508
Remove experimental -Zremap-path-prefix-from/to, and replace it with
the stabilized --remap-path-prefix=from=to variant.
This is an implementation for issue of #41555.
The previous method ran into problems because ICH would treat Spans
as (file,line,col) but the cache contained byte offsets and its
possible for the latter to change while the former stayed stable.
We already had a cache for file contents, but we read the source-file
before testing the cache, causing obvious slowness, so this just avoids
loading the source-file when the cache already has the contents.
* The lazy loading mechanism has been moved to a more appropriate place.
* Return values from the functions invoked there are properly used.
* Documentation has gotten some minor improvements.
* Possibly some larger restructuring will need to take place still.
They are now handled in their own member to prevent mutating access to
the `src` member. This way, we can safely load external sources, while
keeping the mutation of local source strings off-limits.
The rationale is that BOM stripping is needed for lazy source loading
for external crates, and duplication can be avoided by moving the
corresponding functionality to libsyntax_pos.
We can use these to perform lazy loading of source files belonging to
external crates. That way we will be able to show the source code of
external spans that have been translated.
```rust
error[E0072]: recursive type `X` has infinite size
--> file.rs:10:1
|
10 | struct X {
| ^^^^^^^^ recursive type has infinite size
|
= help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `X` representable
```
vs
```rust
error[E0072]: recursive type `X` has infinite size
--> file.rs:10:1
|
10 | struct X {
| _^ starting here...
11 | | x: X,
12 | | }
| |_^ ...ending here: recursive type has infinite size
|
= help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `X` representable
```
