diff --git a/src/api/definitions/mod.rs b/src/api/definitions/mod.rs
index 33c29c92..e0caef31 100644
--- a/src/api/definitions/mod.rs
+++ b/src/api/definitions/mod.rs
@@ -9,7 +9,7 @@ use crate::{Engine, Module, Scope, INT};
 
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
-use std::{any::type_name, borrow::Cow, cmp::Ordering, fmt, fmt::Write};
+use std::{any::type_name, borrow::Cow, cmp::Ordering, fmt};
 
 impl Engine {
     /// _(metadata, internals)_ Return [`Definitions`] that can be used to generate definition files
@@ -186,6 +186,8 @@ impl Definitions<'_> {
 
         #[cfg(not(feature = "no_module"))]
         {
+            use std::fmt::Write;
+
             for (module_name, module_def) in self.modules_impl(&config) {
                 write!(
                     &mut def_file,
@@ -382,6 +384,7 @@ impl Definitions<'_> {
 
 impl Module {
     /// Return definitions for all items inside the [`Module`].
+    #[cfg(not(feature = "no_module"))]
     fn definition(&self, def: &Definitions) -> String {
         let mut s = String::new();
         self.write_definition(&mut s, def).unwrap();
diff --git a/src/ast/ast.rs b/src/ast/ast.rs
index 55a4bc76..cabd7c10 100644
--- a/src/ast/ast.rs
+++ b/src/ast/ast.rs
@@ -213,6 +213,7 @@ impl AST {
     #[cfg(feature = "metadata")]
     #[inline(always)]
     #[must_use]
+    #[allow(dead_code)]
     pub(crate) fn doc_mut(&mut self) -> &mut crate::SmartString {
         &mut self.doc
     }
diff --git a/src/engine.rs b/src/engine.rs
index 265a3aa0..4c63be00 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -14,11 +14,7 @@ use crate::{
 };
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
-use std::{
-    collections::{BTreeMap, BTreeSet},
-    fmt,
-    num::NonZeroU8,
-};
+use std::{collections::BTreeSet, fmt, num::NonZeroU8};
 
 pub type Precedence = NonZeroU8;
 
@@ -99,7 +95,7 @@ pub struct Engine {
     pub(crate) global_modules: StaticVec<Shared<Module>>,
     /// A collection of all sub-modules directly loaded into the Engine.
     #[cfg(not(feature = "no_module"))]
-    pub(crate) global_sub_modules: BTreeMap<Identifier, Shared<Module>>,
+    pub(crate) global_sub_modules: std::collections::BTreeMap<Identifier, Shared<Module>>,
 
     /// A module resolution service.
     #[cfg(not(feature = "no_module"))]
@@ -112,10 +108,11 @@ pub struct Engine {
     pub(crate) disabled_symbols: BTreeSet<Identifier>,
     /// A map containing custom keywords and precedence to recognize.
     #[cfg(not(feature = "no_custom_syntax"))]
-    pub(crate) custom_keywords: BTreeMap<Identifier, Option<Precedence>>,
+    pub(crate) custom_keywords: std::collections::BTreeMap<Identifier, Option<Precedence>>,
     /// Custom syntax.
     #[cfg(not(feature = "no_custom_syntax"))]
-    pub(crate) custom_syntax: BTreeMap<Identifier, crate::api::custom_syntax::CustomSyntax>,
+    pub(crate) custom_syntax:
+        std::collections::BTreeMap<Identifier, crate::api::custom_syntax::CustomSyntax>,
     /// Callback closure for filtering variable definition.
     pub(crate) def_var_filter: Option<Box<OnDefVarCallback>>,
     /// Callback closure for resolving variable access.
@@ -265,7 +262,7 @@ impl Engine {
             global_modules: StaticVec::new_const(),
 
             #[cfg(not(feature = "no_module"))]
-            global_sub_modules: BTreeMap::new(),
+            global_sub_modules: std::collections::BTreeMap::new(),
 
             #[cfg(not(feature = "no_module"))]
             module_resolver: Box::new(crate::module::resolvers::DummyModuleResolver::new()),
@@ -273,9 +270,9 @@ impl Engine {
             interned_strings: StringsInterner::new().into(),
             disabled_symbols: BTreeSet::new(),
             #[cfg(not(feature = "no_custom_syntax"))]
-            custom_keywords: BTreeMap::new(),
+            custom_keywords: std::collections::BTreeMap::new(),
             #[cfg(not(feature = "no_custom_syntax"))]
-            custom_syntax: BTreeMap::new(),
+            custom_syntax: std::collections::BTreeMap::new(),
 
             def_var_filter: None,
             resolve_var: None,
diff --git a/src/eval/global_state.rs b/src/eval/global_state.rs
index 28c0589f..7421a95a 100644
--- a/src/eval/global_state.rs
+++ b/src/eval/global_state.rs
@@ -1,6 +1,6 @@
 //! Global runtime state.
 
-use crate::{Dynamic, Engine, Identifier, ImmutableString};
+use crate::{Dynamic, Engine, Identifier};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{fmt, marker::PhantomData};
@@ -9,7 +9,7 @@ use std::{fmt, marker::PhantomData};
 #[cfg(not(feature = "no_module"))]
 #[cfg(not(feature = "no_function"))]
 pub type GlobalConstants =
-    crate::Shared<crate::Locked<std::collections::BTreeMap<ImmutableString, Dynamic>>>;
+    crate::Shared<crate::Locked<std::collections::BTreeMap<crate::ImmutableString, Dynamic>>>;
 
 /// _(internals)_ Global runtime states.
 /// Exported under the `internals` feature only.
@@ -25,7 +25,7 @@ pub type GlobalConstants =
 pub struct GlobalRuntimeState<'a> {
     /// Stack of module names.
     #[cfg(not(feature = "no_module"))]
-    keys: crate::StaticVec<ImmutableString>,
+    keys: crate::StaticVec<crate::ImmutableString>,
     /// Stack of imported [modules][crate::Module].
     #[cfg(not(feature = "no_module"))]
     modules: crate::StaticVec<crate::Shared<crate::Module>>,
@@ -169,7 +169,7 @@ impl GlobalRuntimeState<'_> {
     #[inline(always)]
     pub fn push_import(
         &mut self,
-        name: impl Into<ImmutableString>,
+        name: impl Into<crate::ImmutableString>,
         module: impl Into<crate::Shared<crate::Module>>,
     ) {
         self.keys.push(name.into());
@@ -205,7 +205,7 @@ impl GlobalRuntimeState<'_> {
     #[inline]
     pub(crate) fn iter_imports_raw(
         &self,
-    ) -> impl Iterator<Item = (&ImmutableString, &crate::Shared<crate::Module>)> {
+    ) -> impl Iterator<Item = (&crate::ImmutableString, &crate::Shared<crate::Module>)> {
         self.keys.iter().rev().zip(self.modules.iter().rev())
     }
     /// Get an iterator to the stack of globally-imported [modules][crate::Module] in forward order.
@@ -216,7 +216,7 @@ impl GlobalRuntimeState<'_> {
     #[inline]
     pub fn scan_imports_raw(
         &self,
-    ) -> impl Iterator<Item = (&ImmutableString, &crate::Shared<crate::Module>)> {
+    ) -> impl Iterator<Item = (&crate::ImmutableString, &crate::Shared<crate::Module>)> {
         self.keys.iter().zip(self.modules.iter())
     }
     /// Does the specified function hash key exist in the stack of globally-imported
@@ -310,9 +310,9 @@ impl GlobalRuntimeState<'_> {
 
 #[cfg(not(feature = "no_module"))]
 impl IntoIterator for GlobalRuntimeState<'_> {
-    type Item = (ImmutableString, crate::Shared<crate::Module>);
+    type Item = (crate::ImmutableString, crate::Shared<crate::Module>);
     type IntoIter = std::iter::Zip<
-        std::iter::Rev<smallvec::IntoIter<[ImmutableString; 3]>>,
+        std::iter::Rev<smallvec::IntoIter<[crate::ImmutableString; 3]>>,
         std::iter::Rev<smallvec::IntoIter<[crate::Shared<crate::Module>; 3]>>,
     >;
 
@@ -327,9 +327,9 @@ impl IntoIterator for GlobalRuntimeState<'_> {
 
 #[cfg(not(feature = "no_module"))]
 impl<'a> IntoIterator for &'a GlobalRuntimeState<'_> {
-    type Item = (&'a ImmutableString, &'a crate::Shared<crate::Module>);
+    type Item = (&'a crate::ImmutableString, &'a crate::Shared<crate::Module>);
     type IntoIter = std::iter::Zip<
-        std::iter::Rev<std::slice::Iter<'a, ImmutableString>>,
+        std::iter::Rev<std::slice::Iter<'a, crate::ImmutableString>>,
         std::iter::Rev<std::slice::Iter<'a, crate::Shared<crate::Module>>>,
     >;
 
@@ -341,7 +341,7 @@ impl<'a> IntoIterator for &'a GlobalRuntimeState<'_> {
 }
 
 #[cfg(not(feature = "no_module"))]
-impl<K: Into<ImmutableString>, M: Into<crate::Shared<crate::Module>>> Extend<(K, M)>
+impl<K: Into<crate::ImmutableString>, M: Into<crate::Shared<crate::Module>>> Extend<(K, M)>
     for GlobalRuntimeState<'_>
 {
     #[inline]
diff --git a/src/packages/lang_core.rs b/src/packages/lang_core.rs
index 379fd4c7..5c073146 100644
--- a/src/packages/lang_core.rs
+++ b/src/packages/lang_core.rs
@@ -1,6 +1,6 @@
 use crate::def_package;
 use crate::plugin::*;
-use crate::types::{dynamic::Tag, StringsInterner};
+use crate::types::dynamic::Tag;
 use crate::{Dynamic, RhaiResultOf, ERR, INT};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -129,12 +129,12 @@ fn collect_fn_metadata(
     filter: impl Fn(FnNamespace, FnAccess, &str, usize, &crate::Shared<crate::ast::ScriptFnDef>) -> bool
         + Copy,
 ) -> crate::Array {
-    use crate::{ast::ScriptFnDef, Array, Identifier, Map};
+    use crate::{ast::ScriptFnDef, Array, Map};
 
     // Create a metadata record for a function.
     fn make_metadata(
-        dict: &mut StringsInterner,
-        #[cfg(not(feature = "no_module"))] namespace: Identifier,
+        dict: &mut crate::types::StringsInterner,
+        #[cfg(not(feature = "no_module"))] namespace: crate::Identifier,
         func: &ScriptFnDef,
     ) -> Map {
         let mut map = Map::new();
@@ -179,7 +179,7 @@ fn collect_fn_metadata(
         map
     }
 
-    let dict = &mut StringsInterner::new();
+    let dict = &mut crate::types::StringsInterner::new();
     let mut list = Array::new();
 
     ctx.iter_namespaces()
@@ -190,7 +190,7 @@ fn collect_fn_metadata(
                 make_metadata(
                     dict,
                     #[cfg(not(feature = "no_module"))]
-                    Identifier::new_const(),
+                    crate::Identifier::new_const(),
                     f,
                 )
                 .into(),
@@ -207,7 +207,7 @@ fn collect_fn_metadata(
                 make_metadata(
                     dict,
                     #[cfg(not(feature = "no_module"))]
-                    Identifier::new_const(),
+                    crate::Identifier::new_const(),
                     f,
                 )
                 .into(),
@@ -225,7 +225,7 @@ fn collect_fn_metadata(
                 make_metadata(
                     dict,
                     #[cfg(not(feature = "no_module"))]
-                    Identifier::new_const(),
+                    crate::Identifier::new_const(),
                     f,
                 )
                 .into(),
@@ -236,7 +236,7 @@ fn collect_fn_metadata(
     {
         // Recursively scan modules for script-defined functions.
         fn scan_module(
-            dict: &mut StringsInterner,
+            dict: &mut crate::types::StringsInterner,
             list: &mut Array,
             namespace: &str,
             module: &Module,
diff --git a/src/packages/mod.rs b/src/packages/mod.rs
index c41c721d..ab4df033 100644
--- a/src/packages/mod.rs
+++ b/src/packages/mod.rs
@@ -83,6 +83,7 @@ pub trait Package {
     ///
     /// package.register_into_engine_as(&mut engine, "core");
     /// ```
+    #[cfg(not(feature = "no_module"))]
     fn register_into_engine_as(&self, engine: &mut Engine, name: &str) -> &Self {
         Self::init_engine(engine);
         engine.register_static_module(name, self.as_shared_module());
diff --git a/src/parser.rs b/src/parser.rs
index 2bf5d3b9..754513c8 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -187,12 +187,13 @@ impl<'e> ParseState<'e> {
         lib: &FnLib,
         pos: Position,
     ) -> (Option<NonZeroUsize>, bool) {
+        let _lib = lib;
         let _pos = pos;
 
         let (index, hit_barrier) = self.find_var(name);
 
         #[cfg(not(feature = "no_function"))]
-        let is_func_name = lib.values().any(|f| f.name == name);
+        let is_func_name = _lib.values().any(|f| f.name == name);
 
         #[cfg(feature = "no_function")]
         let is_func_name = false;
diff --git a/src/serde/metadata.rs b/src/serde/metadata.rs
index d792119a..f4d9732f 100644
--- a/src/serde/metadata.rs
+++ b/src/serde/metadata.rs
@@ -2,7 +2,7 @@
 #![cfg(feature = "metadata")]
 
 use crate::module::{calc_native_fn_hash, FuncInfo};
-use crate::{calc_fn_hash, Engine, FnAccess, FnNamespace, SmartString, StaticVec, AST};
+use crate::{calc_fn_hash, Engine, FnAccess, SmartString, StaticVec, AST};
 use serde::Serialize;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -30,7 +30,7 @@ struct FnMetadata<'a> {
     pub base_hash: u64,
     pub full_hash: u64,
     #[cfg(not(feature = "no_module"))]
-    pub namespace: FnNamespace,
+    pub namespace: crate::FnNamespace,
     pub access: FnAccess,
     pub name: &'a str,
     #[serde(rename = "type")]
@@ -184,7 +184,7 @@ pub fn gen_metadata_to_json(
             let mut meta: FnMetadata = f.into();
             #[cfg(not(feature = "no_module"))]
             {
-                meta.namespace = FnNamespace::Global;
+                meta.namespace = crate::FnNamespace::Global;
             }
             global.functions.push(meta);
         });
@@ -196,7 +196,7 @@ pub fn gen_metadata_to_json(
             let mut meta: FnMetadata = f.into();
             #[cfg(not(feature = "no_module"))]
             {
-                meta.namespace = FnNamespace::Global;
+                meta.namespace = crate::FnNamespace::Global;
             }
             global.functions.push(meta);
         }
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
index 62d120e5..a2ca3fcd 100644
--- a/src/tokenizer.rs
+++ b/src/tokenizer.rs
@@ -333,22 +333,29 @@ impl Span {
 }
 
 impl fmt::Display for Span {
+    #[inline]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let _f = f;
+
+        #[cfg(not(feature = "no_position"))]
         match (self.start(), self.end()) {
-            (Position::NONE, Position::NONE) => write!(f, "{:?}", Position::NONE),
-            (Position::NONE, end) => write!(f, "..{:?}", end),
-            (start, Position::NONE) => write!(f, "{:?}", start),
+            (Position::NONE, Position::NONE) => write!(_f, "{:?}", Position::NONE),
+            (Position::NONE, end) => write!(_f, "..{:?}", end),
+            (start, Position::NONE) => write!(_f, "{:?}", start),
             (start, end) if start.line() != end.line() => {
-                write!(f, "{:?}-{:?}", start, end)
+                write!(_f, "{:?}-{:?}", start, end)
             }
             (start, end) => write!(
-                f,
+                _f,
                 "{}:{}-{}",
                 start.line().unwrap(),
                 start.position().unwrap_or(0),
                 end.position().unwrap_or(0)
             ),
         }
+
+        #[cfg(feature = "no_position")]
+        Ok(())
     }
 }
 
diff --git a/src/types/dynamic.rs b/src/types/dynamic.rs
index 1a37cd16..a318581b 100644
--- a/src/types/dynamic.rs
+++ b/src/types/dynamic.rs
@@ -1,7 +1,7 @@
 //! Helper module which defines the [`Dynamic`] data type and the
 //! [`Any`] trait to to allow custom type handling.
 
-use crate::func::{locked_read, SendSync};
+use crate::func::SendSync;
 use crate::{reify, ExclusiveRange, FnPtr, ImmutableString, InclusiveRange, INT};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -23,6 +23,7 @@ pub use std::time::Instant;
 pub use instant::Instant;
 
 /// The message: data type was checked
+#[allow(dead_code)]
 const CHECKED: &str = "data type was checked";
 
 mod private {
@@ -427,7 +428,7 @@ impl Dynamic {
             Union::Variant(ref v, ..) => (***v).type_id(),
 
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(ref cell, ..) => (*locked_read(cell)).type_id(),
+            Union::Shared(ref cell, ..) => (*crate::func::locked_read(cell)).type_id(),
         }
     }
     /// Get the name of the type of the value held by this [`Dynamic`].
@@ -501,7 +502,7 @@ impl Hash for Dynamic {
             Union::FnPtr(ref f, ..) => f.hash(state),
 
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(ref cell, ..) => (*locked_read(cell)).hash(state),
+            Union::Shared(ref cell, ..) => (*crate::func::locked_read(cell)).hash(state),
 
             Union::Variant(..) => unimplemented!("{} cannot be hashed", self.type_name()),
 
@@ -1073,7 +1074,7 @@ impl Dynamic {
     pub fn is_read_only(&self) -> bool {
         #[cfg(not(feature = "no_closure"))]
         if let Union::Shared(ref cell, ..) = self.0 {
-            return match locked_read(cell).access_mode() {
+            return match crate::func::locked_read(cell).access_mode() {
                 ReadWrite => false,
                 ReadOnly => true,
             };
@@ -1102,7 +1103,7 @@ impl Dynamic {
             Union::Map(..) => true,
 
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(ref cell, ..) => locked_read(cell).is_hashable(),
+            Union::Shared(ref cell, ..) => crate::func::locked_read(cell).is_hashable(),
 
             _ => false,
         }
@@ -1353,7 +1354,7 @@ impl Dynamic {
     pub fn flatten_clone(&self) -> Self {
         match self.0 {
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(ref cell, ..) => locked_read(cell).clone(),
+            Union::Shared(ref cell, ..) => crate::func::locked_read(cell).clone(),
             _ => self.clone(),
         }
     }
@@ -1369,7 +1370,7 @@ impl Dynamic {
         match self.0 {
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(cell, ..) => crate::func::shared_try_take(cell).map_or_else(
-                |ref cell| locked_read(cell).clone(),
+                |ref cell| crate::func::locked_read(cell).clone(),
                 #[cfg(not(feature = "sync"))]
                 |value| value.into_inner(),
                 #[cfg(feature = "sync")]
@@ -1391,7 +1392,7 @@ impl Dynamic {
             Union::Shared(ref mut cell, ..) => {
                 let cell = mem::take(cell);
                 *self = crate::func::shared_try_take(cell).map_or_else(
-                    |ref cell| locked_read(cell).clone(),
+                    |ref cell| crate::func::locked_read(cell).clone(),
                     #[cfg(not(feature = "sync"))]
                     |value| value.into_inner(),
                     #[cfg(feature = "sync")]
@@ -1440,7 +1441,7 @@ impl Dynamic {
         match self.0 {
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(ref cell, ..) => {
-                let value = locked_read(cell);
+                let value = crate::func::locked_read(cell);
 
                 return if (*value).type_id() != TypeId::of::<T>()
                     && TypeId::of::<Dynamic>() != TypeId::of::<T>()
@@ -1788,7 +1789,7 @@ impl Dynamic {
             Union::Str(s, ..) => Ok(s),
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(ref cell, ..) => {
-                let value = locked_read(cell);
+                let value = crate::func::locked_read(cell);
 
                 match value.0 {
                     Union::Str(ref s, ..) => Ok(s.clone()),
@@ -1807,7 +1808,7 @@ impl Dynamic {
             Union::Array(a, ..) => Ok(*a),
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(ref cell, ..) => {
-                let value = locked_read(cell);
+                let value = crate::func::locked_read(cell);
 
                 match value.0 {
                     Union::Array(ref a, ..) => Ok(a.as_ref().clone()),
@@ -1842,7 +1843,7 @@ impl Dynamic {
             Union::Blob(..) if TypeId::of::<T>() == TypeId::of::<u8>() => Ok(self.cast::<Vec<T>>()),
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(ref cell, ..) => {
-                let value = locked_read(cell);
+                let value = crate::func::locked_read(cell);
 
                 match value.0 {
                     Union::Array(ref a, ..) => {
@@ -1880,7 +1881,7 @@ impl Dynamic {
             Union::Blob(a, ..) => Ok(*a),
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(ref cell, ..) => {
-                let value = locked_read(cell);
+                let value = crate::func::locked_read(cell);
 
                 match value.0 {
                     Union::Blob(ref a, ..) => Ok(a.as_ref().clone()),
diff --git a/src/types/interner.rs b/src/types/interner.rs
index 8ce63284..90c28461 100644
--- a/src/types/interner.rs
+++ b/src/types/interner.rs
@@ -127,6 +127,7 @@ impl StringsInterner<'_> {
     /// Number of strings interned.
     #[inline(always)]
     #[must_use]
+    #[allow(dead_code)]
     pub fn len(&self) -> usize {
         self.strings.len()
     }
@@ -134,12 +135,14 @@ impl StringsInterner<'_> {
     /// Returns `true` if there are no interned strings.
     #[inline(always)]
     #[must_use]
+    #[allow(dead_code)]
     pub fn is_empty(&self) -> bool {
         self.strings.is_empty()
     }
 
     /// Clear all interned strings.
     #[inline(always)]
+    #[allow(dead_code)]
     pub fn clear(&mut self) {
         self.strings.clear();
     }
diff --git a/tests/packages.rs b/tests/packages.rs
index 75537721..06d64e52 100644
--- a/tests/packages.rs
+++ b/tests/packages.rs
@@ -7,6 +7,7 @@ def_package! {
         m.set_native_fn("hello", |x: INT| Ok(x + 1));
         m.set_native_fn("@", |x: INT, y: INT| Ok(x * x + y * y));
     } |> |engine| {
+        #[cfg(not(feature = "no_custom_syntax"))]
         engine.register_custom_operator("@", 160).unwrap();
     }
 }
@@ -30,11 +31,20 @@ fn test_packages() -> Result<(), Box<EvalAltResult>> {
         scope.push("x", x);
 
         // Evaluate script.
-        engine.eval_with_scope::<INT>(&mut scope, "hello(x) @ foo::hello(x)")
+
+        #[cfg(not(feature = "no_custom_syntax"))]
+        return engine.eval_with_scope::<INT>(&mut scope, "hello(x) @ foo::hello(x)");
+
+        #[cfg(feature = "no_custom_syntax")]
+        return engine.eval_with_scope::<INT>(&mut scope, "hello(x) + foo::hello(x)");
     };
 
+    #[cfg(not(feature = "no_custom_syntax"))]
     assert_eq!(make_call(42)?, 3698);
 
+    #[cfg(feature = "no_custom_syntax")]
+    assert_eq!(make_call(42)?, 86);
+
     Ok(())
 }