bare_trait_objects suggestion JSON includes stray suggestion

[ehuss]

Given the following code:

pub type T = Copy;

Running rustc foo.rs --error=format=json produces two machine-applicable suggestions. One of them is an empty span which has no effect. The relevant part of the JSON output is:

{
    "message": "use `dyn`",
    "code": null,
    "level": "help",
    "spans":
    [
        {
            "file_name": "foo.rs",
            "byte_start": 13,
            "byte_end": 13,
            "line_start": 1,
            "line_end": 1,
            "column_start": 14,
            "column_end": 14,
            "is_primary": true,
            "text":
            [
                {
                    "text": "pub type T = Copy;",
                    "highlight_start": 14,
                    "highlight_end": 14
                }
            ],
            "label": null,
            "suggested_replacement": "dyn ",
            "suggestion_applicability": "MachineApplicable",
            "expansion": null
        },
        {
            "file_name": "foo.rs",
            "byte_start": 17,
            "byte_end": 17,
            "line_start": 1,
            "line_end": 1,
            "column_start": 18,
            "column_end": 18,
            "is_primary": true,
            "text":
            [
                {
                    "text": "pub type T = Copy;",
                    "highlight_start": 18,
                    "highlight_end": 18
                }
            ],
            "label": null,
            "suggested_replacement": "",
            "suggestion_applicability": "MachineApplicable",
            "expansion": null
        }
    ],
    "children":
    [],
    "rendered": null
}

Notice that the second suggestion is an empty string for an empty span.

I expect this to not emit an empty span suggestion.

rustc 1.66.0-nightly (8b0c05d9a 2022-10-07)
binary: rustc
commit-hash: 8b0c05d9ad7121cdb97600f261bcd5f04c8db20d
commit-date: 2022-10-07
host: x86_64-apple-darwin
release: 1.66.0-nightly
LLVM version: 15.0.2

[compiler-errors]

I bet this is the span to insert ) if it's a complex trait object that needs parens. While this can probably be fixed in that one case specifically, it's probably better to filter multipart suggestion parts that are empty spans with empty replacements out of the list before emitting them as JSON.

This shouldn't be too hard.

[kper]

@rustbot claim

[kper]

@ehuss the fix was merged. Can you close the ticket?

[ehuss]

Indeed, thanks!