Switch to proc_macro_error2

Fixes #441.

proc_macro_error is marked as unmaintained in rustsec:
https://rustsec.org/advisories/RUSTSEC-2024-0370.html

Because proc_macro_error2 removed automatic nightly detection, the error
messages changed slightly.

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+- Switch to `proc_macro_error2`
+  [#441](https://github.com/lambda-fairy/maud/issues/441)
+  [#442](https://github.com/lambda-fairy/maud/pull/442)
+
 ## [0.26.0] - 2024-01-15
 
 - Remove `AsRef<str>` restriction from `PreEscaped`

maud/tests/warnings/keyword-without-at.stderr

@@ -1,7 +1,8 @@
 error: found keyword `if`
+
+         = help: should this be a `@if`?
+
  --> $DIR/keyword-without-at.rs:5:9
   |
 5 |         if {}
   |         ^^
-  |
-  = help: should this be a `@if`?

maud/tests/warnings/non-string-literal.stderr

@@ -35,19 +35,21 @@ error: expected string
    |         ^^^^
 
 error: attribute value must be a string
+
+         = help: to declare an empty attribute, omit the equals sign: `disabled`
+         = help: to toggle the attribute, use square brackets: `disabled[some_boolean_flag]`
+
   --> tests/warnings/non-string-literal.rs:13:24
    |
 13 |         input disabled=true;
    |                        ^^^^
-   |
-   = help: to declare an empty attribute, omit the equals sign: `disabled`
-   = help: to toggle the attribute, use square brackets: `disabled[some_boolean_flag]`
 
 error: attribute value must be a string
+
+         = help: to declare an empty attribute, omit the equals sign: `disabled`
+         = help: to toggle the attribute, use square brackets: `disabled[some_boolean_flag]`
+
   --> tests/warnings/non-string-literal.rs:14:24
    |
 14 |         input disabled=false;
    |                        ^^^^^
-   |
-   = help: to declare an empty attribute, omit the equals sign: `disabled`
-   = help: to toggle the attribute, use square brackets: `disabled[some_boolean_flag]`

maud/tests/warnings/void-element-slash.stderr

@@ -1,17 +1,19 @@
 error: void elements must use `;`, not `/`
+
+         = help: change this to `;`
+         = help: see https://github.com/lambda-fairy/maud/pull/315 for details
+
  --> $DIR/void-element-slash.rs:5:12
   |
 5 |         br /
   |            ^
-  |
-  = help: change this to `;`
-  = help: see https://github.com/lambda-fairy/maud/pull/315 for details
 
 error: void elements must use `;`, not `/`
+
+         = help: change this to `;`
+         = help: see https://github.com/lambda-fairy/maud/pull/315 for details
+
  --> $DIR/void-element-slash.rs:7:27
   |
 7 |         input type="text" /
   |                           ^
-  |
-  = help: change this to `;`
-  = help: see https://github.com/lambda-fairy/maud/pull/315 for details

maud_macros/Cargo.toml

@@ -15,7 +15,7 @@ edition.workspace = true
 syn = "2"
 quote = "1.0.7"
 proc-macro2 = "1.0.23"
-proc-macro-error = { version = "1.0.0", default-features = false }
+proc-macro-error2 = { version = "2.0.1", default-features = false }
 
 [lib]
 name = "maud_macros"

maud_macros/src/ast.rs

@@ -1,5 +1,5 @@
 use proc_macro2::{TokenStream, TokenTree};
-use proc_macro_error::SpanRange;
+use proc_macro_error2::SpanRange;
 use syn::Lit;
 
 #[derive(Debug)]

maud_macros/src/generate.rs

@@ -1,5 +1,5 @@
 use proc_macro2::{Delimiter, Group, Ident, Literal, Span, TokenStream, TokenTree};
-use proc_macro_error::SpanRange;
+use proc_macro_error2::SpanRange;
 use quote::quote;
 
 use crate::{ast::*, escape};

maud_macros/src/lib.rs

@@ -11,7 +11,7 @@ mod generate;
 mod parse;
 
 use proc_macro2::{Ident, Span, TokenStream, TokenTree};
-use proc_macro_error::proc_macro_error;
+use proc_macro_error2::proc_macro_error;
 use quote::quote;
 
 #[proc_macro]

maud_macros/src/parse.rs

@@ -1,5 +1,5 @@
 use proc_macro2::{Delimiter, Ident, Literal, Spacing, Span, TokenStream, TokenTree};
-use proc_macro_error::{abort, abort_call_site, emit_error, SpanRange};
+use proc_macro_error2::{abort, abort_call_site, emit_error, SpanRange};
 use std::collections::HashMap;
 
 use syn::Lit;