change error type for trailing commas, fixes #352

[fmoor]

NOTE: There is one small defect with this patch. The line and column numbers that the error message reports match the position of the closing brace after the trailing comma and not the position of the trailing comma.

I plant to continue searching for the logic that determines the line and column numbers. If someone wants to speed things up and point me towards the relevant code it would be much appreciated.

[dtolnay]

I would go a step further and add an error variant that specifically means trailing comma. "Trailing characters" is pretty ambiguous.

[fmoor]

There is still the problem of reporting misleading line and column numbers.

[fmoor]

@dtolnay why are there suddenly a bunch of clippy errors in code I haven't touched? Should I make all of the suggested changes?

[dtolnay]

Clippy adds new lints occasionally. I filed #354 to follow up.

[dtolnay]

Thanks!