From 65009dd19301a81c873daeca299d0bb5a083cf96 Mon Sep 17 00:00:00 2001
From: J Henry Waugh <jhwgh1968@protonmail.com>
Date: Fri, 21 Aug 2020 23:21:56 -0500
Subject: [PATCH] Block #[cfg] attributes on inner constants

---
 codegen/src/module.rs                    | 34 +++++++++++++++---------
 codegen/ui_tests/module_cfg_const.rs     | 31 +++++++++++++++++++++
 codegen/ui_tests/module_cfg_const.stderr | 11 ++++++++
 3 files changed, 63 insertions(+), 13 deletions(-)
 create mode 100644 codegen/ui_tests/module_cfg_const.rs
 create mode 100644 codegen/ui_tests/module_cfg_const.stderr

diff --git a/codegen/src/module.rs b/codegen/src/module.rs
index 7aa98409..34b67876 100644
--- a/codegen/src/module.rs
+++ b/codegen/src/module.rs
@@ -199,7 +199,7 @@ impl Parse for Module {
     fn parse(input: ParseStream) -> syn::Result<Self> {
         let mut mod_all: syn::ItemMod = input.parse()?;
         let fns: Vec<_>;
-        let consts: Vec<_>;
+        let mut consts: Vec<_> = new_vec![];
         let mut submodules: Vec<_> = Vec::new();
         if let Some((_, ref mut content)) = mod_all.content {
             // Gather and parse functions.
@@ -223,24 +223,33 @@ impl Parse for Module {
                         .map(|_| vec)
                 })?;
             // Gather and parse constants definitions.
-            consts = content
-                .iter()
-                .filter_map(|item| match item {
+            for item in content.iter() {
+                match item {
                     syn::Item::Const(syn::ItemConst {
                         vis,
                         ref expr,
                         ident,
+                        attrs,
                         ..
                     }) => {
-                        if let syn::Visibility::Public(_) = vis {
-                            Some((ident.to_string(), expr.as_ref().clone()))
-                        } else {
-                            None
+                        // #[cfg] attributes are not allowed on const declarations
+                        if let Some(cfg_attr) = attrs.iter().find(|a| {
+                            a.path
+                                .get_ident()
+                                .map(|i| i.to_string() == "cfg")
+                                .unwrap_or(false)
+                        }) {
+                            return Err(syn::Error::new(
+                                    cfg_attr.span(),
+                                    "cfg attributes not allowed on this item"));
                         }
-                    }
-                    _ => None,
-                })
-                .collect();
+                        if let syn::Visibility::Public(_) = vis {
+                            consts.push((ident.to_string(), expr.as_ref().clone()));
+                        }
+                    },
+                    _ => {},
+                }
+            };
             // Gather and parse submodule definitions.
             //
             // They are actually removed from the module's body, because they will need
@@ -270,7 +279,6 @@ impl Parse for Module {
                 }
             }
         } else {
-            consts = new_vec![];
             fns = new_vec![];
         }
         Ok(Module {
diff --git a/codegen/ui_tests/module_cfg_const.rs b/codegen/ui_tests/module_cfg_const.rs
new file mode 100644
index 00000000..599f52da
--- /dev/null
+++ b/codegen/ui_tests/module_cfg_const.rs
@@ -0,0 +1,31 @@
+use rhai::plugin::*;
+
+#[derive(Clone)]
+pub struct Point {
+    x: f32,
+    y: f32,
+}
+
+#[export_module]
+pub mod test_module {
+    use rhai::FLOAT;
+
+    #[cfg(feature = "foo")]
+    pub const MAGIC: FLOAT = 42.0 as FLOAT;
+
+    pub fn test_fn(input: Point) -> bool {
+        input.x > input.y
+    }
+}
+
+fn main() {
+    let n = Point {
+        x: 0.0,
+        y: 10.0,
+    };
+    if test_module::test_fn(n) {
+        println!("yes");
+    } else {
+        println!("no");
+    }
+}
diff --git a/codegen/ui_tests/module_cfg_const.stderr b/codegen/ui_tests/module_cfg_const.stderr
new file mode 100644
index 00000000..4eaf1b06
--- /dev/null
+++ b/codegen/ui_tests/module_cfg_const.stderr
@@ -0,0 +1,11 @@
+error: cfg attributes not allowed on this item
+  --> $DIR/module_cfg_const.rs:13:5
+   |
+13 |     #[cfg(feature = "foo")]
+   |     ^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0433]: failed to resolve: use of undeclared type or module `test_module`
+  --> $DIR/module_cfg_const.rs:26:8
+   |
+26 |     if test_module::test_fn(n) {
+   |        ^^^^^^^^^^^ use of undeclared type or module `test_module`