diff --git a/src/api/build_type.rs b/src/api/build_type.rs
index ae83def26..5b5e77a66 100644
--- a/src/api/build_type.rs
+++ b/src/api/build_type.rs
@@ -98,7 +98,6 @@ impl Engine {
 ///
 /// To define a pretty-print name, call [`with_name`][`TypeBuilder::with_name`],
 /// to use [`Engine::register_type_with_name`] instead.
-#[must_use]
 pub struct TypeBuilder<'a, T: Variant + Clone> {
     engine: &'a mut Engine,
     name: Option<&'static str>,
diff --git a/src/api/call_fn.rs b/src/api/call_fn.rs
index 3206755d3..bba9a2586 100644
--- a/src/api/call_fn.rs
+++ b/src/api/call_fn.rs
@@ -14,7 +14,6 @@ use std::{any::type_name, mem};
 /// Options for calling a script-defined function via [`Engine::call_fn_with_options`].
 #[derive(Debug, Hash)]
 #[non_exhaustive]
-#[must_use]
 pub struct CallFnOptions<'t> {
     /// A value for binding to the `this` pointer (if any). Default [`None`].
     pub this_ptr: Option<&'t mut Dynamic>,
@@ -36,6 +35,7 @@ impl Default for CallFnOptions<'_> {
 impl<'a> CallFnOptions<'a> {
     /// Create a default [`CallFnOptions`].
     #[inline(always)]
+    #[must_use]
     pub fn new() -> Self {
         Self {
             this_ptr: None,
@@ -46,24 +46,28 @@ impl<'a> CallFnOptions<'a> {
     }
     /// Bind to the `this` pointer.
     #[inline(always)]
+    #[must_use]
     pub fn bind_this_ptr(mut self, value: &'a mut Dynamic) -> Self {
         self.this_ptr = Some(value);
         self
     }
     /// Set the custom state of this evaluation run (if any).
     #[inline(always)]
+    #[must_use]
     pub fn with_tag(mut self, value: impl Variant + Clone) -> Self {
         self.tag = Some(Dynamic::from(value));
         self
     }
     /// Set whether to evaluate the [`AST`] to load necessary modules before calling the function.
     #[inline(always)]
+    #[must_use]
     pub const fn eval_ast(mut self, value: bool) -> Self {
         self.eval_ast = value;
         self
     }
     /// Set whether to rewind the [`Scope`] after the function call.
     #[inline(always)]
+    #[must_use]
     pub const fn rewind_scope(mut self, value: bool) -> Self {
         self.rewind_scope = value;
         self
diff --git a/src/ast/script_fn.rs b/src/ast/script_fn.rs
index 5be3ba1d2..a566871a2 100644
--- a/src/ast/script_fn.rs
+++ b/src/ast/script_fn.rs
@@ -75,17 +75,30 @@ impl fmt::Display for ScriptFnDef {
 ///
 /// Created by [`AST::iter_functions`][super::AST::iter_functions].
 #[derive(Debug, Eq, PartialEq, Ord, PartialOrd, Clone, Hash)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Serialize, serde::Deserialize),
+    serde(rename_all = "camelCase")
+)]
 #[non_exhaustive]
 pub struct ScriptFnMetadata<'a> {
     /// Function name.
     pub name: &'a str,
     /// Function parameters (if any).
+    #[cfg_attr(
+        feature = "serde",
+        serde(default, skip_serializing_if = "Vec::is_empty")
+    )]
     pub params: Vec<&'a str>,
     /// Function access mode.
     pub access: FnAccess,
-    #[cfg(not(feature = "no_object"))]
     /// Type of `this` pointer, if any.
     /// Not available under `no_object`.
+    #[cfg(not(feature = "no_object"))]
+    #[cfg_attr(
+        feature = "serde",
+        serde(default, skip_serializing_if = "Option::is_none")
+    )]
     pub this_type: Option<&'a str>,
     /// _(metadata)_ Function doc-comments (if any).
     /// Exported under the `metadata` feature only.
@@ -102,6 +115,10 @@ pub struct ScriptFnMetadata<'a> {
     ///
     /// Each line in non-block doc-comments starts with `///`.
     #[cfg(feature = "metadata")]
+    #[cfg_attr(
+        feature = "serde",
+        serde(default, skip_serializing_if = "Vec::is_empty")
+    )]
     pub comments: Vec<&'a str>,
 }
 
diff --git a/src/eval/chaining.rs b/src/eval/chaining.rs
index 8c0fd67de..66b7ea73e 100644
--- a/src/eval/chaining.rs
+++ b/src/eval/chaining.rs
@@ -21,6 +21,7 @@ static INDEXER_HASHES: OnceCell<(u64, u64)> = OnceCell::new();
 #[must_use]
 fn hash_idx() -> (u64, u64) {
     *INDEXER_HASHES.get_or_init(|| {
+        #[allow(clippy::useless_conversion)]
         (
             calc_fn_hash(None, FN_IDX_GET, 2),
             calc_fn_hash(None, FN_IDX_SET, 3),
diff --git a/src/lib.rs b/src/lib.rs
index 2eb92d205..88187e57e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -54,7 +54,9 @@
 //!
 //! # Features
 //!
-#![cfg_attr(feature = "document-features", doc = document_features::document_features!(feature_label = "<span id=\"feature-{feature}\">**`{feature}`**</span>"))]
+#![cfg_attr(feature = "document-features", doc = document_features::document_features!(
+    feature_label = "<span id=\"feature-{feature}\">**`{feature}`**</span>"
+))]
 //!
 //! # On-Line Documentation
 //!
diff --git a/src/serde/metadata.rs b/src/serde/metadata.rs
index bbc16d272..8d8bfb0a4 100644
--- a/src/serde/metadata.rs
+++ b/src/serde/metadata.rs
@@ -20,9 +20,9 @@ enum FnType {
 #[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct FnParam<'a> {
-    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(default, skip_serializing_if = "Option::is_none")]
     pub name: Option<&'a str>,
-    #[serde(rename = "type", skip_serializing_if = "Option::is_none")]
+    #[serde(rename = "type", default, skip_serializing_if = "Option::is_none")]
     pub typ: Option<Cow<'a, str>>,
 }
 
@@ -164,14 +164,14 @@ impl<'a> From<&'a FuncInfo> for FnMetadata<'a> {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct ModuleMetadata<'a> {
-    #[serde(skip_serializing_if = "str::is_empty")]
-    pub doc: &'a str,
-    #[serde(skip_serializing_if = "BTreeMap::is_empty")]
+    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
     pub modules: BTreeMap<&'a str, Self>,
-    #[serde(skip_serializing_if = "Vec::is_empty")]
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub custom_types: Vec<CustomTypeMetadata<'a>>,
-    #[serde(skip_serializing_if = "Vec::is_empty")]
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub functions: Vec<FnMetadata<'a>>,
+    #[serde(default, skip_serializing_if = "str::is_empty")]
+    pub doc: &'a str,
 }
 
 impl ModuleMetadata<'_> {
diff --git a/src/serde/ser.rs b/src/serde/ser.rs
index c4030dbde..d76975368 100644
--- a/src/serde/ser.rs
+++ b/src/serde/ser.rs
@@ -15,9 +15,9 @@ use num_traits::FromPrimitive;
 /// Serializer for [`Dynamic`][crate::Dynamic].
 pub struct DynamicSerializer {
     /// Buffer to hold a temporary key.
-    _key: Identifier,
+    key: Identifier,
     /// Buffer to hold a temporary value.
-    _value: Dynamic,
+    value: Dynamic,
 }
 
 impl DynamicSerializer {
@@ -25,8 +25,8 @@ impl DynamicSerializer {
     #[must_use]
     pub const fn new(value: Dynamic) -> Self {
         Self {
-            _key: Identifier::new_const(),
-            _value: value,
+            key: Identifier::new_const(),
+            value,
         }
     }
 }
@@ -464,7 +464,7 @@ impl SerializeSeq for DynamicSerializer {
         #[cfg(not(feature = "no_index"))]
         {
             let value = _value.serialize(&mut *self)?;
-            let arr = self._value.downcast_mut::<crate::Array>().unwrap();
+            let arr = self.value.downcast_mut::<crate::Array>().unwrap();
             arr.push(value);
             Ok(())
         }
@@ -481,7 +481,7 @@ impl SerializeSeq for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_index"))]
-        return Ok(self._value);
+        return Ok(self.value);
         #[cfg(feature = "no_index")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
@@ -500,7 +500,7 @@ impl SerializeTuple for DynamicSerializer {
         #[cfg(not(feature = "no_index"))]
         {
             let value = _value.serialize(&mut *self)?;
-            let arr = self._value.downcast_mut::<crate::Array>().unwrap();
+            let arr = self.value.downcast_mut::<crate::Array>().unwrap();
             arr.push(value);
             Ok(())
         }
@@ -516,7 +516,7 @@ impl SerializeTuple for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_index"))]
-        return Ok(self._value);
+        return Ok(self.value);
         #[cfg(feature = "no_index")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
@@ -535,7 +535,7 @@ impl SerializeTupleStruct for DynamicSerializer {
         #[cfg(not(feature = "no_index"))]
         {
             let value = _value.serialize(&mut *self)?;
-            let arr = self._value.downcast_mut::<crate::Array>().unwrap();
+            let arr = self.value.downcast_mut::<crate::Array>().unwrap();
             arr.push(value);
             Ok(())
         }
@@ -551,7 +551,7 @@ impl SerializeTupleStruct for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_index"))]
-        return Ok(self._value);
+        return Ok(self.value);
         #[cfg(feature = "no_index")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
@@ -570,7 +570,7 @@ impl SerializeMap for DynamicSerializer {
         #[cfg(not(feature = "no_object"))]
         {
             let key = _key.serialize(&mut *self)?;
-            self._key = key
+            self.key = key
                 .into_immutable_string()
                 .map_err(|typ| {
                     ERR::ErrorMismatchDataType("string".into(), typ.into(), Position::NONE)
@@ -590,9 +590,9 @@ impl SerializeMap for DynamicSerializer {
     fn serialize_value<T: ?Sized + Serialize>(&mut self, _value: &T) -> RhaiResultOf<()> {
         #[cfg(not(feature = "no_object"))]
         {
-            let key = std::mem::take(&mut self._key);
+            let key = std::mem::take(&mut self.key);
             let value = _value.serialize(&mut *self)?;
-            let map = self._value.downcast_mut::<crate::Map>().unwrap();
+            let map = self.value.downcast_mut::<crate::Map>().unwrap();
             map.insert(key, value);
             Ok(())
         }
@@ -617,7 +617,7 @@ impl SerializeMap for DynamicSerializer {
                 ERR::ErrorMismatchDataType("string".into(), typ.into(), Position::NONE)
             })?;
             let value = _value.serialize(&mut *self)?;
-            let map = self._value.downcast_mut::<crate::Map>().unwrap();
+            let map = self.value.downcast_mut::<crate::Map>().unwrap();
             map.insert(key.into(), value);
             Ok(())
         }
@@ -633,7 +633,7 @@ impl SerializeMap for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_object"))]
-        return Ok(self._value);
+        return Ok(self.value);
         #[cfg(feature = "no_object")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
@@ -656,7 +656,7 @@ impl SerializeStruct for DynamicSerializer {
         #[cfg(not(feature = "no_object"))]
         {
             let value = _value.serialize(&mut *self)?;
-            let map = self._value.downcast_mut::<crate::Map>().unwrap();
+            let map = self.value.downcast_mut::<crate::Map>().unwrap();
             map.insert(_key.into(), value);
             Ok(())
         }
@@ -672,7 +672,7 @@ impl SerializeStruct for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_object"))]
-        return Ok(self._value);
+        return Ok(self.value);
         #[cfg(feature = "no_object")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
diff --git a/src/types/custom_types.rs b/src/types/custom_types.rs
index 559be5e2b..3419fbb39 100644
--- a/src/types/custom_types.rs
+++ b/src/types/custom_types.rs
@@ -7,7 +7,8 @@ use std::{any::type_name, collections::BTreeMap};
 
 /// _(internals)_ Information for a registered custom type.
 /// Exported under the `internals` feature only.
-#[derive(Debug, Eq, PartialEq, Clone, Hash, Default)]
+#[derive(Debug, Eq, PartialEq, Clone, Hash)]
+#[non_exhaustive]
 pub struct CustomTypeInfo {
     /// Rust name of the custom type.
     pub type_name: Identifier,
diff --git a/src/types/var_def.rs b/src/types/var_def.rs
index c46953c2a..2c83bc715 100644
--- a/src/types/var_def.rs
+++ b/src/types/var_def.rs
@@ -4,7 +4,7 @@
 use std::prelude::v1::*;
 
 /// Information on a variable definition.
-#[derive(Debug, Hash)]
+#[derive(Debug, Clone, Hash)]
 pub struct VarDefInfo<'a> {
     /// Name of the variable to be defined.
     name: &'a str,