diff --git a/crates/wasm-encoder/README.md b/crates/wasm-encoder/README.md
index 5f2efbe210..dc41ab66bc 100644
--- a/crates/wasm-encoder/README.md
+++ b/crates/wasm-encoder/README.md
@@ -36,12 +36,11 @@ let mut module = Module::new();
 let mut types = TypeSection::new();
 let params = vec![ValType::I32, ValType::I32];
 let results = vec![ValType::I32];
-types.function(params, results);
+let type_index = types.function(params, results);
 module.section(&types);
 
 // Encode the function section.
 let mut functions = FunctionSection::new();
-let type_index = 0;
 functions.function(type_index);
 module.section(&functions);
 
diff --git a/crates/wasm-encoder/src/core/code.rs b/crates/wasm-encoder/src/core/code.rs
index 8fd62c0f72..1b051044ce 100644
--- a/crates/wasm-encoder/src/core/code.rs
+++ b/crates/wasm-encoder/src/core/code.rs
@@ -14,10 +14,9 @@ use std::borrow::Cow;
 /// };
 ///
 /// let mut types = TypeSection::new();
-/// types.function(vec![], vec![ValType::I32]);
+/// let type_index = types.function(vec![], vec![ValType::I32]);
 ///
 /// let mut functions = FunctionSection::new();
-/// let type_index = 0;
 /// functions.function(type_index);
 ///
 /// let locals = vec![];
diff --git a/crates/wasm-encoder/src/core/data.rs b/crates/wasm-encoder/src/core/data.rs
index 6439b66e2e..c47074677c 100644
--- a/crates/wasm-encoder/src/core/data.rs
+++ b/crates/wasm-encoder/src/core/data.rs
@@ -81,7 +81,7 @@ impl DataSection {
     }
 
     /// Define a data segment.
-    pub fn segment<D>(&mut self, segment: DataSegment<D>) -> &mut Self
+    pub fn segment<D>(&mut self, segment: DataSegment<D>) -> u32
     where
         D: IntoIterator<Item = u8>,
         D::IntoIter: ExactSizeIterator,
@@ -111,12 +111,13 @@ impl DataSection {
         data.len().encode(&mut self.bytes);
         self.bytes.extend(data);
 
+        let index = self.num_added;
         self.num_added += 1;
-        self
+        index
     }
 
     /// Define an active data segment.
-    pub fn active<D>(&mut self, memory_index: u32, offset: &ConstExpr, data: D) -> &mut Self
+    pub fn active<D>(&mut self, memory_index: u32, offset: &ConstExpr, data: D) -> u32
     where
         D: IntoIterator<Item = u8>,
         D::IntoIter: ExactSizeIterator,
@@ -133,7 +134,7 @@ impl DataSection {
     /// Define a passive data segment.
     ///
     /// Passive data segments are part of the bulk memory proposal.
-    pub fn passive<D>(&mut self, data: D) -> &mut Self
+    pub fn passive<D>(&mut self, data: D) -> u32
     where
         D: IntoIterator<Item = u8>,
         D::IntoIter: ExactSizeIterator,
@@ -145,10 +146,11 @@ impl DataSection {
     }
 
     /// Copy an already-encoded data segment into this data section.
-    pub fn raw(&mut self, already_encoded_data_segment: &[u8]) -> &mut Self {
+    pub fn raw(&mut self, already_encoded_data_segment: &[u8]) -> u32 {
         self.bytes.extend_from_slice(already_encoded_data_segment);
+        let index = self.num_added;
         self.num_added += 1;
-        self
+        index
     }
 }
 
diff --git a/crates/wasm-encoder/src/core/elements.rs b/crates/wasm-encoder/src/core/elements.rs
index 5eb641247b..b67bd42b2c 100644
--- a/crates/wasm-encoder/src/core/elements.rs
+++ b/crates/wasm-encoder/src/core/elements.rs
@@ -102,7 +102,7 @@ impl ElementSection {
     }
 
     /// Define an element segment.
-    pub fn segment<'a>(&mut self, segment: ElementSegment<'a>) -> &mut Self {
+    pub fn segment<'a>(&mut self, segment: ElementSegment<'a>) -> u32 {
         let expr_bit = match segment.elements {
             Elements::Expressions(_) => 0b100u32,
             Elements::Functions(_) => 0b000u32,
@@ -158,8 +158,9 @@ impl ElementSection {
             }
         }
 
+        let index = self.num_added;
         self.num_added += 1;
-        self
+        index
     }
 
     /// Define an active element segment.
@@ -173,7 +174,7 @@ impl ElementSection {
         offset: &ConstExpr,
         element_type: ValType,
         elements: Elements<'_>,
-    ) -> &mut Self {
+    ) -> u32 {
         self.segment(ElementSegment {
             mode: ElementMode::Active {
                 table: table_index,
@@ -187,7 +188,7 @@ impl ElementSection {
     /// Encode a passive element segment.
     ///
     /// Passive segments are part of the bulk memory proposal.
-    pub fn passive<'a>(&mut self, element_type: ValType, elements: Elements<'a>) -> &mut Self {
+    pub fn passive<'a>(&mut self, element_type: ValType, elements: Elements<'a>) -> u32 {
         self.segment(ElementSegment {
             mode: ElementMode::Passive,
             element_type,
@@ -198,7 +199,7 @@ impl ElementSection {
     /// Encode a declared element segment.
     ///
     /// Declared segments are part of the bulk memory proposal.
-    pub fn declared<'a>(&mut self, element_type: ValType, elements: Elements<'a>) -> &mut Self {
+    pub fn declared<'a>(&mut self, element_type: ValType, elements: Elements<'a>) -> u32 {
         self.segment(ElementSegment {
             mode: ElementMode::Declared,
             element_type,
@@ -207,10 +208,11 @@ impl ElementSection {
     }
 
     /// Copy a raw, already-encoded element segment into this elements section.
-    pub fn raw(&mut self, raw_bytes: &[u8]) -> &mut Self {
+    pub fn raw(&mut self, raw_bytes: &[u8]) -> u32 {
         self.bytes.extend_from_slice(raw_bytes);
+        let index = self.num_added;
         self.num_added += 1;
-        self
+        index
     }
 }
 
diff --git a/crates/wasm-encoder/src/core/types.rs b/crates/wasm-encoder/src/core/types.rs
index d99e22ea94..03f9d829e4 100644
--- a/crates/wasm-encoder/src/core/types.rs
+++ b/crates/wasm-encoder/src/core/types.rs
@@ -79,7 +79,7 @@ impl TypeSection {
     }
 
     /// Define a function type in this type section.
-    pub fn function<P, R>(&mut self, params: P, results: R) -> &mut Self
+    pub fn function<P, R>(&mut self, params: P, results: R) -> u32
     where
         P: IntoIterator<Item = ValType>,
         P::IntoIter: ExactSizeIterator,
@@ -94,8 +94,10 @@ impl TypeSection {
         self.bytes.extend(params.map(u8::from));
         results.len().encode(&mut self.bytes);
         self.bytes.extend(results.map(u8::from));
+
+        let index = self.num_added;
         self.num_added += 1;
-        self
+        index
     }
 }
 
diff --git a/crates/wasm-encoder/src/lib.rs b/crates/wasm-encoder/src/lib.rs
index 48a53cf9c7..5d2d8ef5f9 100644
--- a/crates/wasm-encoder/src/lib.rs
+++ b/crates/wasm-encoder/src/lib.rs
@@ -36,12 +36,11 @@
 //! let mut types = TypeSection::new();
 //! let params = vec![ValType::I32, ValType::I32];
 //! let results = vec![ValType::I32];
-//! types.function(params, results);
+//! let type_index = types.function(params, results);
 //! module.section(&types);
 //!
 //! // Encode the function section.
 //! let mut functions = FunctionSection::new();
-//! let type_index = 0;
 //! functions.function(type_index);
 //! module.section(&functions);
 //!
diff --git a/crates/wasm-smith/src/component/encode.rs b/crates/wasm-smith/src/component/encode.rs
index f2bfe734fc..b816404ffd 100644
--- a/crates/wasm-smith/src/component/encode.rs
+++ b/crates/wasm-smith/src/component/encode.rs
@@ -223,7 +223,9 @@ impl Type {
 impl DefinedType {
     fn encode(&self, enc: wasm_encoder::ComponentDefinedTypeEncoder<'_>) {
         match self {
-            Self::Primitive(ty) => enc.primitive(*ty),
+            Self::Primitive(ty) => {
+                enc.primitive(*ty);
+            }
             Self::Record(ty) => {
                 enc.record(ty.fields.iter().map(|(name, ty)| (name.as_str(), *ty)));
             }
diff --git a/crates/wast/src/component/binary.rs b/crates/wast/src/component/binary.rs
index 709c613cfc..dce92978cc 100644
--- a/crates/wast/src/component/binary.rs
+++ b/crates/wast/src/component/binary.rs
@@ -95,7 +95,9 @@ fn encode_type(encoder: ComponentTypeEncoder, ty: &TypeDef) {
 
 fn encode_defined_type(encoder: ComponentDefinedTypeEncoder, ty: &ComponentDefinedType) {
     match ty {
-        ComponentDefinedType::Primitive(p) => encoder.primitive((*p).into()),
+        ComponentDefinedType::Primitive(p) => {
+            encoder.primitive((*p).into());
+        },
         ComponentDefinedType::Record(r) => {
             encoder.record(r.fields.iter().map(|f| (f.name, &f.ty)));
         }
@@ -120,7 +122,9 @@ fn encode_defined_type(encoder: ComponentDefinedTypeEncoder, ty: &ComponentDefin
         ComponentDefinedType::Enum(e) => {
             encoder.enum_type(e.names.iter().copied());
         }
-        ComponentDefinedType::Union(u) => encoder.union(u.types.iter()),
+        ComponentDefinedType::Union(u) => {
+            encoder.union(u.types.iter());
+        },
         ComponentDefinedType::Option(o) => {
             encoder.option(o.element.as_ref());
         }
@@ -820,10 +824,12 @@ impl From<&ModuleType<'_>> for wasm_encoder::ModuleType {
         for decl in &ty.decls {
             match decl {
                 ModuleTypeDecl::Type(t) => match &t.def {
-                    core::TypeDef::Func(f) => encoded.ty().function(
-                        f.params.iter().map(|(_, _, ty)| (*ty).into()),
-                        f.results.iter().copied().map(Into::into),
-                    ),
+                    core::TypeDef::Func(f) => {
+                        encoded.ty().function(
+                            f.params.iter().map(|(_, _, ty)| (*ty).into()),
+                            f.results.iter().copied().map(Into::into),
+                        );
+                    },
                     core::TypeDef::Struct(_) | core::TypeDef::Array(_) => {
                         todo!("encoding of GC proposal types not yet implemented")
                     }