Error tweaks

[cmyr]

With this patch, we now track the path involved anytime we fail to load a .glif or a .plist file.

This also removes the position tracking for errors that occur when parsing glifs; there isn't a great way to get this information from quick_xml, and the information we did have was often inaccurate enough that it wasn't even on the correct line, which made it not very helpful for producing diagnostics.

@madig if you're interested in adding path information to other errors, I think you should be able to follow the pattern I've used here.

[madig]

So the general pattern is, provide specific error types for some things and then wrap them with a path in the top-level Error type?

[madig]

With this branch, changing a content.plist file entry to intentionally point nowhere, I now get

Glif { path: "C:\\...\\Temp\\aaa\\MutatorSansLightWide.ufo\\glyphs\\E__.glif", inner: IoError(Os { code: 2, kind: NotFound, message: "The system cannot find the file specified." }

That's better. The path implicitly also includes the layer name, though it could be presented a bit nicer maybe 🤔

[madig]

Also, this makes the Error::ParseError variant redundant. Maybe I can even get rid of Error::IoError?

[cmyr]

So the general pattern is, provide specific error types for some things and then wrap them with a path in the top-level Error type?

This is a function of the code's "separation of concerns": the glyph parsing code does not know the path, it just receives a pointer to some bytes. This means that whatever error it returns cannot include the path, so we have to add that information later.

If the glif parsing code did happen to know the path, this would be unnecessary, and I would include the path in the error there. I'm not advocating this, though, since the separation of concerns is good for any number of reasons: as a simple example it means that we can test glyph parsing without needing to worry about having the files written to disk.

[cmyr]

okay, fixed up and rebased :)

[github-actions]

🗜 Bloat check ⚖️

Comparing 1bb71e1 against ddaaaf6

target	old size	new size	difference
target/release/examples/load_save	1.86 MB	1.88 MB	18.71 KB (0.98%)
target/debug/examples/load_save	8.43 MB	8.45 MB	27.28 KB (0.32%)

[github-actions]

🗜 Bloat check ⚖️

Comparing ea988e4 against ddaaaf6

target	old size	new size	difference
target/release/examples/load_save	1.86 MB	1.88 MB	18.75 KB (0.99%)
target/debug/examples/load_save	8.43 MB	8.45 MB	27.3 KB (0.32%)

[cmyr]

I can't approve this since I opened it, but I'm happy to merge. :)

[madig]

Approved it for you 😁