Use serde's error message option to avoid implementing Deserialize.

Cargo.toml

@@ -52,7 +52,7 @@ percent-encoding = "2.0"
 rustfix = "0.5.0"
 same-file = "1"
 semver = { version = "0.10", features = ["serde"] }
-serde = { version = "1.0.82", features = ["derive"] }
+serde = { version = "1.0.123", features = ["derive"] }
 serde_ignored = "0.1.0"
 serde_json = { version = "1.0.30", features = ["raw_value"] }
 shell-escape = "0.1.4"

src/cargo/util/toml/mod.rs

@@ -419,53 +419,13 @@ impl ser::Serialize for TomlOptLevel {
     }
 }
 
-#[derive(Clone, Debug, Serialize, Eq, PartialEq)]
-#[serde(untagged)]
+#[derive(Clone, Debug, Deserialize, Serialize, Eq, PartialEq)]
+#[serde(untagged, expecting = "expected a boolean or an integer")]
 pub enum U32OrBool {
     U32(u32),
     Bool(bool),
 }
 
-impl<'de> de::Deserialize<'de> for U32OrBool {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: de::Deserializer<'de>,
-    {
-        struct Visitor;
-
-        impl<'de> de::Visitor<'de> for Visitor {
-            type Value = U32OrBool;
-
-            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
-                formatter.write_str("a boolean or an integer")
-            }
-
-            fn visit_bool<E>(self, b: bool) -> Result<Self::Value, E>
-            where
-                E: de::Error,
-            {
-                Ok(U32OrBool::Bool(b))
-            }
-
-            fn visit_i64<E>(self, u: i64) -> Result<Self::Value, E>
-            where
-                E: de::Error,
-            {
-                Ok(U32OrBool::U32(u as u32))
-            }
-
-            fn visit_u64<E>(self, u: u64) -> Result<Self::Value, E>
-            where
-                E: de::Error,
-            {
-                Ok(U32OrBool::U32(u as u32))
-            }
-        }
-
-        deserializer.deserialize_any(Visitor)
-    }
-}
-
 #[derive(Deserialize, Serialize, Clone, Debug, Default, Eq, PartialEq)]
 #[serde(default, rename_all = "kebab-case")]
 pub struct TomlProfile {
@@ -770,46 +730,13 @@ impl<'de> de::Deserialize<'de> for StringOrVec {
     }
 }
 
-#[derive(Clone, Debug, Serialize, Eq, PartialEq)]
-#[serde(untagged)]
+#[derive(Clone, Debug, Deserialize, Serialize, Eq, PartialEq)]
+#[serde(untagged, expecting = "expected a boolean or a string")]
 pub enum StringOrBool {
     String(String),
     Bool(bool),
 }
 
-impl<'de> de::Deserialize<'de> for StringOrBool {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: de::Deserializer<'de>,
-    {
-        struct Visitor;
-
-        impl<'de> de::Visitor<'de> for Visitor {
-            type Value = StringOrBool;
-
-            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
-                formatter.write_str("a boolean or a string")
-            }
-
-            fn visit_bool<E>(self, b: bool) -> Result<Self::Value, E>
-            where
-                E: de::Error,
-            {
-                Ok(StringOrBool::Bool(b))
-            }
-
-            fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
-            where
-                E: de::Error,
-            {
-                Ok(StringOrBool::String(s.to_string()))
-            }
-        }
-
-        deserializer.deserialize_any(Visitor)
-    }
-}
-
 #[derive(PartialEq, Clone, Debug, Serialize)]
 #[serde(untagged)]
 pub enum VecStringOrBool {

tests/testsuite/bad_config.rs

@@ -1309,7 +1309,7 @@ fn bad_debuginfo() {
 error: failed to parse manifest at `[..]`
 
 Caused by:
-  invalid type: string \"a\", expected a boolean or an integer for [..]
+  expected a boolean or an integer for [..]
 ",
         )
         .run();
@@ -1338,7 +1338,7 @@ fn bad_opt_level() {
 error: failed to parse manifest at `[..]`
 
 Caused by:
-  invalid type: integer `3`, expected a boolean or a string for key [..]
+  expected a boolean or a string for key [..]
 ",
         )
         .run();