From 1be7e60be2e3ae002a52f068c820ad6bd8a2dd8b Mon Sep 17 00:00:00 2001
From: Stephen Chung <schungx@live.com>
Date: Sat, 17 Apr 2021 17:25:35 +0800
Subject: [PATCH] Automatic global module.

---
 CHANGELOG.md       | 12 ++++++++++++
 src/engine.rs      | 21 ++++++++++++++++++++-
 src/fn_call.rs     |  4 ++++
 tests/functions.rs | 17 ++++++++++++++++-
 4 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 50328aab..3ede0882 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,12 +4,24 @@ Rhai Release Notes
 Version 0.20.1
 ==============
 
+This version enables functions to access constants declared at global level via the special `global` module.
+
 Breaking changes
 ----------------
 
 * `Dynamic::is_shared` and `Dynamic::is_locked` are removed under the `no_closure` feature. They used to always return `false`.
 * `Engine::call_fn` now evaluates the `AST` before calling the function.
 
+Enhancements
+------------
+
+* The crate [`no-std-compat`](https://crates.io/crates/no_std_compat) is used to compile for `no-std`. This removes the need to use a special `crate::stdlib` namespace for `std` imports.
+
+New features
+------------
+
+* A module called `global` is automatically created to hold global-level constants, which can then be accessed from functions.
+
 
 Version 0.20.0
 ==============
diff --git a/src/engine.rs b/src/engine.rs
index 7541a56a..8196d18d 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -52,7 +52,10 @@ pub type Precedence = NonZeroU8;
 // the module name will live beyond the AST of the eval script text.
 // The best we can do is a shared reference.
 #[derive(Clone, Default)]
-pub struct Imports(StaticVec<Identifier>, StaticVec<Shared<Module>>);
+pub struct Imports(
+    smallvec::SmallVec<[Identifier; 8]>,
+    smallvec::SmallVec<[Shared<Module>; 8]>,
+);
 
 impl Imports {
     /// Get the length of this stack of imported [modules][Module].
@@ -70,6 +73,12 @@ impl Imports {
     pub fn get(&self, index: usize) -> Option<Shared<Module>> {
         self.1.get(index).cloned()
     }
+    /// Get the imported [modules][Module] at a particular index.
+    #[cfg(not(feature = "no_function"))]
+    #[inline(always)]
+    pub(crate) fn get_mut(&mut self, index: usize) -> Option<&mut Shared<Module>> {
+        self.1.get_mut(index)
+    }
     /// Get the index of an imported [modules][Module] by name.
     #[inline(always)]
     pub fn find(&self, name: &str) -> Option<usize> {
@@ -199,6 +208,8 @@ pub const KEYWORD_IS_DEF_VAR: &str = "is_def_var";
 #[cfg(not(feature = "no_function"))]
 pub const KEYWORD_IS_DEF_FN: &str = "is_def_fn";
 pub const KEYWORD_THIS: &str = "this";
+#[cfg(not(feature = "no_function"))]
+pub const KEYWORD_GLOBAL: &str = "global";
 #[cfg(not(feature = "no_object"))]
 pub const FN_GET: &str = "get$";
 #[cfg(not(feature = "no_object"))]
@@ -2504,6 +2515,14 @@ impl Engine {
                     .flatten();
 
                 let (var_name, _alias): (Cow<'_, str>, _) = if state.is_global() {
+                    #[cfg(not(feature = "no_function"))]
+                    if entry_type == AccessMode::ReadOnly {
+                        let global = mods.get_mut(mods.find(KEYWORD_GLOBAL).unwrap()).unwrap();
+                        let global = Shared::get_mut(global).unwrap();
+                        global.set_var(name.clone(), value.clone());
+                        global.build_index();
+                    }
+
                     (
                         name.to_string().into(),
                         if *export { Some(name.clone()) } else { None },
diff --git a/src/fn_call.rs b/src/fn_call.rs
index 2a5c904c..3840c587 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -826,6 +826,10 @@ impl Engine {
         lib: &[&Module],
         level: usize,
     ) -> RhaiResult {
+        // Create the global module
+        #[cfg(not(feature = "no_function"))]
+        mods.push(crate::engine::KEYWORD_GLOBAL, Module::new());
+
         self.eval_stmt_block(scope, mods, state, lib, &mut None, statements, false, level)
             .or_else(|err| match *err {
                 EvalAltResult::Return(out, _) => Ok(out),
diff --git a/tests/functions.rs b/tests/functions.rs
index 05805a9e..1387f3eb 100644
--- a/tests/functions.rs
+++ b/tests/functions.rs
@@ -62,7 +62,22 @@ fn test_functions_namespaces() -> Result<(), Box<EvalAltResult>> {
     assert_eq!(engine.eval::<INT>("test()")?, 42);
 
     #[cfg(not(feature = "no_function"))]
-    assert_eq!(engine.eval::<INT>("fn test() { 123 } test()")?, 123);
+    {
+        assert_eq!(engine.eval::<INT>("fn test() { 123 } test()")?, 123);
+
+        assert_eq!(
+            engine.eval::<INT>(
+                r"
+                    const ANSWER = 42;
+
+                    fn foo() { global::ANSWER }
+                    
+                    foo()
+                "
+            )?,
+            42
+        );
+    }
 
     Ok(())
 }