From 5b36e375c2f6b0a8189134f34b7c8f5ca3ec28d1 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 9 Nov 2024 22:05:33 -0800
Subject: [PATCH 1/2] Add ui test of invalid expression syntax in display
 attribute

---
 tests/ui/expression-fallback.rs | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 tests/ui/expression-fallback.rs

diff --git a/tests/ui/expression-fallback.rs b/tests/ui/expression-fallback.rs
new file mode 100644
index 0000000..7269129
--- /dev/null
+++ b/tests/ui/expression-fallback.rs
@@ -0,0 +1,7 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+#[error("".yellow)]
+pub struct ArgError;
+
+fn main() {}

From 591a44d9a37b0326e808df7ef38a6a101badab17 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 9 Nov 2024 22:18:07 -0800
Subject: [PATCH 2/2] Fix fallback fmt expression parser hang

---
 impl/src/fmt.rs                     |  2 ++
 tests/ui/expression-fallback.stderr | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 tests/ui/expression-fallback.stderr

diff --git a/impl/src/fmt.rs b/impl/src/fmt.rs
index 3d1394c..d2ab353 100644
--- a/impl/src/fmt.rs
+++ b/impl/src/fmt.rs
@@ -193,6 +193,8 @@ fn fallback_explicit_named_args(input: ParseStream) -> Result<FmtArguments> {
             let ident = input.call(Ident::parse_any)?;
             input.parse::<Token![=]>()?;
             args.named.insert(ident);
+        } else {
+            input.parse::<TokenTree>()?;
         }
     }
 
diff --git a/tests/ui/expression-fallback.stderr b/tests/ui/expression-fallback.stderr
new file mode 100644
index 0000000..5c9f215
--- /dev/null
+++ b/tests/ui/expression-fallback.stderr
@@ -0,0 +1,19 @@
+error: expected `,`, found `.`
+ --> tests/ui/expression-fallback.rs:4:11
+  |
+4 | #[error("".yellow)]
+  |           ^ expected `,`
+
+error: argument never used
+ --> tests/ui/expression-fallback.rs:4:12
+  |
+4 | #[error("".yellow)]
+  |         -- ^^^^^^ argument never used
+  |         |
+  |         formatting specifier missing
+
+error[E0425]: cannot find value `yellow` in this scope
+ --> tests/ui/expression-fallback.rs:4:12
+  |
+4 | #[error("".yellow)]
+  |            ^^^^^^ not found in this scope