Rust Analyzer passes 0-indexed line numbers using proc_macro_span unstable API

[mr-adult]

Rust-analyzer appears to be passing Spans' line numbers (from the proc_macro_span unstable API) as 0-indexed values to my proc-macro. According to the documentation, this line is supposed to always be 1-indexed. The rustc compiler is using 1-indexed lines. The result of this is an LSP error of proc-macro panicked: attempt to subtract with overflow. When compiled and run using rustc, however, the code runs perfectly fine.

rust-analyzer version: 0.3.2273-standalone (248bd51 2025-01-18)
rustc version: 1.84.0-nightly (9b18a122f 2024-10-26)

editor or extension: VSCode. For VSCode users, specify your extension version: 0.3.2273

relevant settings: N/A

repository link (if public, optional): rust-analyzer-bug-report

code snippet to reproduce:

use simpleml_macro::sml;

fn main() {
    let tree = sml!{
        Configuration
            Video
                Resolution 1280 720
                RefreshRate  60
                Fullscreen true
            -
            Audio
                Volume 100
                Music  80
            -
            Player
                Name "Hero 123"
            -
        -
    };
    println!("{tree:?}")
}

[ChayimFriedman2]

You should note that we don't really support the line/column API (and can't, for incrementality reasons). Currently it just returns 0. Returning 1 is trivial, but it won't really mean we support this API.

[mr-adult]

That's fair. I don't think returning 1 would help my use case, but would probably still be more consistent with the Span.line() documentation. Since the syntax of SimpleML is whitespace-sensitive, using the line/column APIs was the best way I could find to achieve whitespace-sensitive syntax in a rust macro.

Probably the most helpful thing that could be done here would be to monitor the line/column APIs and, if they're called, suppress all diagnostics from the macro. That doesn't seem worth the development effort though, so I'd also be okay with closing the issue. I can let my users know in documentation that rust-analyzer doesn't support this macro particularly well and they will see phantom errors.

[ChayimFriedman2]

We can return line/column numbers relative to the macro call's beginning (instead of the file's beginning); will that help you? (Anyway that's not what we're doing currently).

Relying on whitespace information is brittle anyway and macros weren't meant for that. If you'll make the whole argument a string it'll be easier.