From deeda5690617162bf7c7364a2cb3faa69e880a19 Mon Sep 17 00:00:00 2001
From: Dan Parizher <105245560+danparizher@users.noreply.github.com>
Date: Mon, 10 Nov 2025 13:29:35 -0500
Subject: [PATCH] [`configuration`] Fix unclear error messages for line-length
 values exceeding `u16::MAX` (#21329)

Co-authored-by: Micha Reiser <micha@reiser.io>
---
 crates/ruff_linter/src/line_width.rs   | 18 +++++----
 crates/ruff_workspace/src/pyproject.rs | 56 ++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 7 deletions(-)

diff --git a/crates/ruff_linter/src/line_width.rs b/crates/ruff_linter/src/line_width.rs
index c8cf857621..80915c9f59 100644
--- a/crates/ruff_linter/src/line_width.rs
+++ b/crates/ruff_linter/src/line_width.rs
@@ -51,13 +51,17 @@ impl<'de> serde::Deserialize<'de> for LineLength {
     where
         D: serde::Deserializer<'de>,
     {
-        let value = u16::deserialize(deserializer)?;
-        Self::try_from(value).map_err(|_| {
-            serde::de::Error::custom(format!(
-                "line-length must be between 1 and {} (got {value})",
-                Self::MAX,
-            ))
-        })
+        let value = i64::deserialize(deserializer)?;
+
+        u16::try_from(value)
+            .ok()
+            .and_then(|u16_value| Self::try_from(u16_value).ok())
+            .ok_or_else(|| {
+                serde::de::Error::custom(format!(
+                    "line-length must be between 1 and {} (got {value})",
+                    Self::MAX,
+                ))
+            })
     }
 }
 
diff --git a/crates/ruff_workspace/src/pyproject.rs b/crates/ruff_workspace/src/pyproject.rs
index 9cfa01a35d..53649a31e8 100644
--- a/crates/ruff_workspace/src/pyproject.rs
+++ b/crates/ruff_workspace/src/pyproject.rs
@@ -468,6 +468,62 @@ line-length = 500
             "line-length must be between 1 and 320 (got 500)"
         );
 
+        // Test value at u16::MAX boundary (65535) - should show range error
+        let invalid_line_length_65535 = toml::from_str::<Pyproject>(
+            r"
+[tool.ruff]
+line-length = 65535
+",
+        )
+        .expect_err("Deserialization should have failed for line-length at u16::MAX");
+
+        assert_eq!(
+            invalid_line_length_65535.message(),
+            "line-length must be between 1 and 320 (got 65535)"
+        );
+
+        // Test value exceeding u16::MAX (65536) - should show clear error
+        let invalid_line_length_65536 = toml::from_str::<Pyproject>(
+            r"
+[tool.ruff]
+line-length = 65536
+",
+        )
+        .expect_err("Deserialization should have failed for line-length exceeding u16::MAX");
+
+        assert_eq!(
+            invalid_line_length_65536.message(),
+            "line-length must be between 1 and 320 (got 65536)"
+        );
+
+        // Test value far exceeding u16::MAX (99_999) - should show clear error
+        let invalid_line_length_99999 = toml::from_str::<Pyproject>(
+            r"
+[tool.ruff]
+line-length = 99_999
+",
+        )
+        .expect_err("Deserialization should have failed for line-length far exceeding u16::MAX");
+
+        assert_eq!(
+            invalid_line_length_99999.message(),
+            "line-length must be between 1 and 320 (got 99999)"
+        );
+
+        // Test negative value - should show clear error
+        let invalid_line_length_negative = toml::from_str::<Pyproject>(
+            r"
+[tool.ruff]
+line-length = -5
+",
+        )
+        .expect_err("Deserialization should have failed for negative line-length");
+
+        assert_eq!(
+            invalid_line_length_negative.message(),
+            "line-length must be between 1 and 320 (got -5)"
+        );
+
         Ok(())
     }