[`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

@@ -51,13 +51,17 @@ impl<'de> serde::Deserialize<'de> for LineLength {
     where
         D: serde::Deserializer<'de>,
     {
-        let value = u16::deserialize(deserializer)?;
+        let value = i64::deserialize(deserializer)?;
-        Self::try_from(value).map_err(|_| {
+
-            serde::de::Error::custom(format!(
+        u16::try_from(value)
-                "line-length must be between 1 and {} (got {value})",
+            .ok()
-                Self::MAX,
+            .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,
+                ))
+            })
     }
 }
 

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(())
     }