serde::json macro invocation failed to parse

[extremegf]

This is a new problem, as the snippets that now fail in my codebase used to be handled without issue.

I did some bisecting. This worked fine on v0.2.400 and fails on v0.2.408. It also fails on v0.2.416, albeit with a smaller red highlight.

Steps to reproduce:

lib.rs

use serde_json::json;

fn foo() {
    json!({ "a": "b" });
}

Cargo.toml

[dependencies]
serde = "1.0"
serde_json = "1"

Observe that the json! call is highlighted red with "failed to parse macro invocation".

[flodiebold]

It probably failed to expand before those versions; we just didn't have the diagnostic yet. You can disable the error for now by adding "macro-error" to the rust-analyzer.diagnostics.disabled setting.

[flodiebold]

This was also reported as a comment in #6704, but it might not be the same issue.

[lnicola]

Reproducer:

macro_rules! json_internal {
    ({ $tt:tt }) => {
        let _ = 42;
    };
}

fn main() {
    json_internal!({ "a" });
}

[flodiebold]

Hmm that looks like the same expanding-to-statements problem as #6811 then. Which actually #6704 is probably as well.

[lnicola]

That's right. Closing as duplicate of #6811.

[extremegf]

It probably failed to expand before those versions; we just didn't have the diagnostic yet. You can disable the error for now by adding "macro-error" to the rust-analyzer.diagnostics.disabled setting.

Thank you. That's a useful workaround!

I'm impressed at how quickly this was analyzed by the RA team.