Derive Default for structs when all field defaults are intrinsic

cargo-typify/tests/outputs/attr.rs

@@ -174,18 +174,10 @@ pub struct Veggie {
 #[doc = r" ```"]
 #[doc = r" </details>"]
 #[extra_attr]
-#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug)]
+#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug, Default)]
 pub struct Veggies {
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub fruits: ::std::vec::Vec<::std::string::String>,
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub vegetables: ::std::vec::Vec<Veggie>,
 }
-impl ::std::default::Default for Veggies {
-    fn default() -> Self {
-        Self {
-            fruits: Default::default(),
-            vegetables: Default::default(),
-        }
-    }
-}

cargo-typify/tests/outputs/builder.rs

@@ -175,21 +175,13 @@ impl Veggie {
 #[doc = "}"]
 #[doc = r" ```"]
 #[doc = r" </details>"]
-#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug)]
+#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug, Default)]
 pub struct Veggies {
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub fruits: ::std::vec::Vec<::std::string::String>,
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub vegetables: ::std::vec::Vec<Veggie>,
 }
-impl ::std::default::Default for Veggies {
-    fn default() -> Self {
-        Self {
-            fruits: Default::default(),
-            vegetables: Default::default(),
-        }
-    }
-}
 impl Veggies {
     pub fn builder() -> builder::Veggies {
         Default::default()

cargo-typify/tests/outputs/custom_btree_map.rs

@@ -176,21 +176,13 @@ impl Veggie {
 #[doc = "}"]
 #[doc = r" ```"]
 #[doc = r" </details>"]
-#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug)]
+#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug, Default)]
 pub struct Veggies {
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub fruits: ::std::vec::Vec<::std::string::String>,
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub vegetables: ::std::vec::Vec<Veggie>,
 }
-impl ::std::default::Default for Veggies {
-    fn default() -> Self {
-        Self {
-            fruits: Default::default(),
-            vegetables: Default::default(),
-        }
-    }
-}
 impl Veggies {
     pub fn builder() -> builder::Veggies {
         Default::default()

cargo-typify/tests/outputs/derive.rs

@@ -170,18 +170,10 @@ pub struct Veggie {
 #[doc = "}"]
 #[doc = r" ```"]
 #[doc = r" </details>"]
-#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug, ExtraDerive)]
+#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug, Default, ExtraDerive)]
 pub struct Veggies {
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub fruits: ::std::vec::Vec<::std::string::String>,
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub vegetables: ::std::vec::Vec<Veggie>,
 }
-impl ::std::default::Default for Veggies {
-    fn default() -> Self {
-        Self {
-            fruits: Default::default(),
-            vegetables: Default::default(),
-        }
-    }
-}

cargo-typify/tests/outputs/multi_derive.rs

@@ -177,19 +177,17 @@ pub struct Veggie {
 #[doc = r" ```"]
 #[doc = r" </details>"]
 #[derive(
-    :: serde :: Deserialize, :: serde :: Serialize, AnotherDerive, Clone, Debug, ExtraDerive,
+    :: serde :: Deserialize,
+    :: serde :: Serialize,
+    AnotherDerive,
+    Clone,
+    Debug,
+    Default,
+    ExtraDerive,
 )]
 pub struct Veggies {
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub fruits: ::std::vec::Vec<::std::string::String>,
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub vegetables: ::std::vec::Vec<Veggie>,
 }
-impl ::std::default::Default for Veggies {
-    fn default() -> Self {
-        Self {
-            fruits: Default::default(),
-            vegetables: Default::default(),
-        }
-    }
-}

cargo-typify/tests/outputs/no-builder.rs

@@ -170,18 +170,10 @@ pub struct Veggie {
 #[doc = "}"]
 #[doc = r" ```"]
 #[doc = r" </details>"]
-#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug)]
+#[derive(:: serde :: Deserialize, :: serde :: Serialize, Clone, Debug, Default)]
 pub struct Veggies {
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub fruits: ::std::vec::Vec<::std::string::String>,
     #[serde(default, skip_serializing_if = "::std::vec::Vec::is_empty")]
     pub vegetables: ::std::vec::Vec<Veggie>,
 }
-impl ::std::default::Default for Veggies {
-    fn default() -> Self {
-        Self {
-            fruits: Default::default(),
-            vegetables: Default::default(),
-        }
-    }
-}

typify-impl/src/type_entry.rs

@@ -1111,7 +1111,7 @@ impl TypeEntry {
         type_space: &TypeSpace,
         output: &mut OutputSpace,
         struct_details: &TypeEntryStruct,
-        derive_set: BTreeSet<&str>,
+        mut derive_set: BTreeSet<&str>,
     ) {
         enum PropDefault {
             None(String),
@@ -1193,6 +1193,19 @@ impl TypeEntry {
             });
         });
 
+        // If there's no whole-type default value and every property's default
+        // is the intrinsic `Default::default()`, the hand-written `impl Default`
+        // would be exactly what `#[derive(Default)]` produces (and would trip
+        // clippy's `derivable_impls` lint downstream). In that case we derive
+        // `Default` rather than emitting the manual impl below.
+        let derive_default = default.is_none()
+            && prop_default
+                .iter()
+                .all(|pd| matches!(pd, PropDefault::Default(_)));
+        if derive_default {
+            derive_set.insert("Default");
+        }
+
         let derives = strings_to_derives(
             derive_set,
             &self.extra_derives,
@@ -1233,6 +1246,8 @@ impl TypeEntry {
                     }
                 },
             );
+        } else if derive_default {
+            // Handled above via `#[derive(Default)]`.
         } else if let Some(prop_default) = prop_default
             .iter()
             .map(|pd| match pd {