From c357f9728e4c5497dec5128d8ed258b82bbd163a Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 2 Nov 2024 21:05:30 -0700
Subject: [PATCH 1/2] Add infallible expr scanner fallback for scanning invalid
 code

---
 impl/src/fmt.rs | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/impl/src/fmt.rs b/impl/src/fmt.rs
index df75044..a15aeb6 100644
--- a/impl/src/fmt.rs
+++ b/impl/src/fmt.rs
@@ -1,10 +1,11 @@
 use crate::ast::Field;
 use crate::attr::{Display, Trait};
 use crate::scan_expr;
-use proc_macro2::TokenTree;
+use proc_macro2::{TokenStream, TokenTree};
 use quote::{format_ident, quote, quote_spanned};
 use std::collections::{BTreeSet as Set, HashMap as Map};
 use syn::ext::IdentExt;
+use syn::parse::discouraged::Speculative;
 use syn::parse::{ParseStream, Parser};
 use syn::{Expr, Ident, Index, LitStr, Member, Result, Token};
 
@@ -119,6 +120,23 @@ impl Display<'_> {
 }
 
 fn explicit_named_args(input: ParseStream) -> Result<Set<Ident>> {
+    let ahead = input.fork();
+    if let Ok(set) = try_explicit_named_args(&ahead) {
+        input.advance_to(&ahead);
+        return Ok(set);
+    }
+
+    let ahead = input.fork();
+    if let Ok(set) = fallback_explicit_named_args(&ahead) {
+        input.advance_to(&ahead);
+        return Ok(set);
+    }
+
+    input.parse::<TokenStream>().unwrap();
+    Ok(Set::new())
+}
+
+fn try_explicit_named_args(input: ParseStream) -> Result<Set<Ident>> {
     let scan_expr = if is_syn_full() {
         |input: ParseStream| input.parse::<Expr>().map(drop)
     } else {
@@ -143,6 +161,21 @@ fn explicit_named_args(input: ParseStream) -> Result<Set<Ident>> {
     Ok(named_args)
 }
 
+fn fallback_explicit_named_args(input: ParseStream) -> Result<Set<Ident>> {
+    let mut named_args = Set::new();
+
+    while !input.is_empty() {
+        if input.peek(Token![,]) && input.peek2(Ident::peek_any) && input.peek3(Token![=]) {
+            input.parse::<Token![,]>()?;
+            let ident = input.call(Ident::parse_any)?;
+            input.parse::<Token![=]>()?;
+            named_args.insert(ident);
+        }
+    }
+
+    Ok(named_args)
+}
+
 fn is_syn_full() -> bool {
     // Expr::Block contains syn::Block which contains Vec<syn::Stmt>. In the
     // current version of Syn, syn::Stmt is exhaustive and could only plausibly

From 0ab908aab0dc12415ce34241fdc23bb722bd0eba Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 2 Nov 2024 21:12:28 -0700
Subject: [PATCH 2/2] Ignore expected unnecessary_wraps pedantic clippy lint

    warning: this function's return value is unnecessarily wrapped by `Result`
       --> impl/src/fmt.rs:122:1
        |
    122 | / fn explicit_named_args(input: ParseStream) -> Result<Set<Ident>> {
    123 | |     let ahead = input.fork();
    124 | |     if let Ok(set) = try_explicit_named_args(&ahead) {
    125 | |         input.advance_to(&ahead);
    ...   |
    136 | |     Ok(Set::new())
    137 | | }
        | |_^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_wraps
        = note: `-W clippy::unnecessary-wraps` implied by `-W clippy::pedantic`
        = help: to override `-W clippy::pedantic` add `#[allow(clippy::unnecessary_wraps)]`
    help: remove `Result` from the return type...
        |
    122 | fn explicit_named_args(input: ParseStream) -> std::collections::BTreeSet<proc_macro2::Ident> {
        |                                               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    help: ...and then change returning expressions
        |
    126 ~         return set;
    127 |     }
    ...
    131 |         input.advance_to(&ahead);
    132 ~         return set;
    133 |     }
    134 |
    135 |     input.parse::<TokenStream>().unwrap();
    136 ~     Set::new()
        |
---
 impl/src/fmt.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/impl/src/fmt.rs b/impl/src/fmt.rs
index a15aeb6..153a423 100644
--- a/impl/src/fmt.rs
+++ b/impl/src/fmt.rs
@@ -119,6 +119,7 @@ impl Display<'_> {
     }
 }
 
+#[allow(clippy::unnecessary_wraps)]
 fn explicit_named_args(input: ParseStream) -> Result<Set<Ident>> {
     let ahead = input.fork();
     if let Ok(set) = try_explicit_named_args(&ahead) {