Proc macro crash with the unquote crate

[lnicola]

Here's a smaller reproduction that builds on stable Rust 1.57.0:

[package]
name = "macro-test"
version = "0.0.0"
edition = "2021"
publish = false

[lib]
# Needed because `unquote`'s syn dependency isn't set up correctly. It's hopefully not relevant.
proc_macro = true

[dependencies]
quote = "1.0.10"
syn = "1.0.83"
unquote = "0.0.6"

use quote::quote;
use syn::parse::ParseStream;
use unquote::unquote;

#[allow(dead_code)]
fn parse(input: ParseStream) -> syn::Result<()> {
    unquote!(input, a); // <--
    Ok(())
}

Settings (not minimal):

{
    "rust-analyzer.cargo-watch.command": "clippy",
    "rust-analyzer.rainbowHighlightingOn": true,
    "rust-analyzer.procMacro.enabled": true,
    "rust-analyzer.procMacro.enable": true,
    "rust-analyzer.cargo.loadOutDirsFromCheck": true,
    "rust-analyzer.checkOnSave.command": "clippy",
    "rust-analyzer.experimental.procAttrMacros": true,
    "rust-analyzer.cargo.allFeatures": true,
    "rust-analyzer.checkOnSave.extraArgs": [
        "--locked"
    ],
    "rust-analyzer.updates.channel": "nightly"
}

---

cargo expand:

Probably not relevant, but it's a fairly simple macro:

#![feature(prelude_import)]
#[prelude_import]
use std::prelude::rust_2021::*;
#[macro_use]
extern crate std;
use quote::quote;
use syn::parse::ParseStream;
use unquote::unquote;
#[allow(dead_code)]
fn parse(input: ParseStream) -> syn::Result<()> {
    let input = input;
    let mut prev_span = input.cursor().span();
    if input.call(<syn::Ident as syn::ext::IdentExt>::parse_any)?
        != syn::parse::Parser::parse2(<syn::Ident as syn::ext::IdentExt>::parse_any, {
            let mut _s = ::quote::__private::TokenStream::new();
            ::quote::__private::push_ident(&mut _s, "a");
            _s
        })
        .unwrap()
    {
        return Err(syn::Error::new(input.cursor().span(), "Expected `a`"));
    };
    Ok(())
}
const _: () = {
    extern crate proc_macro;
    #[rustc_proc_macro_decls]
    #[allow(deprecated)]
    static _DECLS: &[proc_macro::bridge::client::ProcMacro] = &[];
};

---

Error:

[{
	"resource": "[project directory]/src/lib.rs",
	"owner": "rustc",
	"code": {
		"value": "macro-error",
		"target": {
			"$mid": 1,
			"external": "https://rust-analyzer.github.io/manual.html#macro-error",
			"path": "/manual.html",
			"scheme": "https",
			"authority": "rust-analyzer.github.io",
			"fragment": "macro-error"
		}
	},
	"severity": 8,
	"message": "called `Option::unwrap()` on a `None` value",
	"source": "rust-analyzer",
	"startLineNumber": 7,
	"startColumn": 5,
	"endLineNumber": 7,
	"endColumn": 23
}]

---

Rust Analyzer Client output (abbreviated):

INFO [25.12.2021, 18:38:34]: Extension version: 0.3.875
INFO [25.12.2021, 18:38:34]: Using configuration {
  […]
}
INFO [25.12.2021, 18:38:34]: PersistentState: { serverVersion: '0.3.875' }
INFO [25.12.2021, 18:38:34]: Using server binary at [~]\.vscode\extensions\matklad.rust-analyzer-0.3.875\server\rust-analyzer.exe

Rust Analyzer Language Server Trace appears to be empty.

Originally posted by @Tamschi in #10570 (comment)

[brandondong]

I tried editing the unquote crate implementation and trimming down the code/dependencies to the bare minimum that reproduces the issue:

use proc_macro::{Span, TokenStream};

#[proc_macro]
pub fn unquote(_input: TokenStream) -> TokenStream {
	let span = Span::call_site();
	span.located_at(span);
	TokenStream::new()
}

The located_at line results in the Option.unwrap error. It doesn't seem to matter how you get the two Span's. The same thing happens for calling resolved_at.

Looking at https://github.com/rust-analyzer/rust-analyzer/blob/7409880a07803c34590ad162d7854061145c6eae/crates/proc_macro_srv/src/abis/abi_1_56/rustc_server.rs#L690, I'm really not sure why this happens.

[Tamschi]

This may be fixed, or at least I'm now getting a stack overflow in the rust-analyzer language server instead of this error in my project.

[Veykril]

This should be fixed as we changed the logic here to no longer be ID based