diff --git a/src/api/compile.rs b/src/api/compile.rs
index b9e95e50..78424402 100644
--- a/src/api/compile.rs
+++ b/src/api/compile.rs
@@ -222,10 +222,10 @@ impl Engine {
             self.token_mapper.as_ref().map(<_>::as_ref),
         );
         let mut state = ParseState::new(self, scope, tokenizer_control);
-        let mut ast = self.parse(&mut stream.peekable(), &mut state, optimization_level)?;
+        let mut _ast = self.parse(&mut stream.peekable(), &mut state, optimization_level)?;
         #[cfg(feature = "metadata")]
-        ast.set_doc(state.tokenizer_control.borrow().global_comments.join("\n"));
-        Ok(ast)
+        _ast.set_doc(state.tokenizer_control.borrow().global_comments.join("\n"));
+        Ok(_ast)
     }
     /// Compile a string containing an expression into an [`AST`],
     /// which can be used later for evaluation.
diff --git a/src/api/optimize.rs b/src/api/optimize.rs
index 726b12f9..f790a803 100644
--- a/src/api/optimize.rs
+++ b/src/api/optimize.rs
@@ -2,7 +2,6 @@
 #![cfg(not(feature = "no_optimize"))]
 
 use crate::{Engine, OptimizationLevel, Scope, AST};
-use std::mem;
 
 impl Engine {
     /// Control whether and how the [`Engine`] will optimize an [`AST`] after compilation.
@@ -60,7 +59,7 @@ impl Engine {
             .map(|f| f.func.get_script_fn_def().unwrap().clone())
             .collect();
 
-        let mut new_ast = crate::optimizer::optimize_into_ast(
+        let mut _new_ast = crate::optimizer::optimize_into_ast(
             self,
             scope,
             ast.take_statements(),
@@ -70,8 +69,8 @@ impl Engine {
         );
 
         #[cfg(feature = "metadata")]
-        new_ast.set_doc(mem::take(ast.doc_mut()));
+        _new_ast.set_doc(std::mem::take(ast.doc_mut()));
 
-        new_ast
+        _new_ast
     }
 }
diff --git a/src/ast/ast.rs b/src/ast/ast.rs
index 0d21651f..854ce431 100644
--- a/src/ast/ast.rs
+++ b/src/ast/ast.rs
@@ -1,7 +1,7 @@
 //! Module defining the AST (abstract syntax tree).
 
 use super::{ASTFlags, Expr, FnAccess, Stmt, StmtBlock, StmtBlockContainer};
-use crate::{Dynamic, FnNamespace, Identifier, Position, SmartString};
+use crate::{Dynamic, FnNamespace, Identifier, Position};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{
@@ -23,7 +23,7 @@ pub struct AST {
     source: Identifier,
     /// [`AST`] documentation.
     #[cfg(feature = "metadata")]
-    doc: SmartString,
+    doc: crate::SmartString,
     /// Global statements.
     body: StmtBlock,
     /// Script-defined functions.
@@ -76,7 +76,7 @@ impl AST {
         Self {
             source: Identifier::new_const(),
             #[cfg(feature = "metadata")]
-            doc: SmartString::new_const(),
+            doc: crate::SmartString::new_const(),
             body: StmtBlock::new(statements, Position::NONE, Position::NONE),
             #[cfg(not(feature = "no_function"))]
             lib: functions.into(),
@@ -96,7 +96,7 @@ impl AST {
         Self {
             source: Identifier::new_const(),
             #[cfg(feature = "metadata")]
-            doc: SmartString::new_const(),
+            doc: crate::SmartString::new_const(),
             body: StmtBlock::new(statements, Position::NONE, Position::NONE),
             #[cfg(not(feature = "no_function"))]
             lib: functions.into(),
@@ -146,7 +146,7 @@ impl AST {
         Self {
             source: Identifier::new_const(),
             #[cfg(feature = "metadata")]
-            doc: SmartString::new_const(),
+            doc: crate::SmartString::new_const(),
             body: StmtBlock::NONE,
             #[cfg(not(feature = "no_function"))]
             lib: crate::Module::new().into(),
@@ -213,7 +213,7 @@ impl AST {
     #[cfg(feature = "metadata")]
     #[inline(always)]
     #[must_use]
-    pub(crate) fn doc_mut(&mut self) -> &mut SmartString {
+    pub(crate) fn doc_mut(&mut self) -> &mut crate::SmartString {
         &mut self.doc
     }
     /// Set the documentation.
@@ -221,7 +221,7 @@ impl AST {
     /// Only available under `metadata`.
     #[cfg(feature = "metadata")]
     #[inline(always)]
-    pub(crate) fn set_doc(&mut self, doc: impl Into<SmartString>) {
+    pub(crate) fn set_doc(&mut self, doc: impl Into<crate::SmartString>) {
         self.doc = doc.into();
     }
     /// Get the statements.