From 3b42cc5bb2306c2d24f78c522a63bc7501c92be7 Mon Sep 17 00:00:00 2001
From: Stephen Chung <schungx@live.com>
Date: Sat, 23 Jan 2021 09:37:27 +0800
Subject: [PATCH] Fix bug where plugin module parameters are consumed.

---
 RELEASES.md      |  1 +
 src/fn_call.rs   | 35 +++++++++++++----------------------
 tests/plugins.rs | 29 +++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+), 22 deletions(-)

diff --git a/RELEASES.md b/RELEASES.md
index 2fec4b9e..904627bc 100644
--- a/RELEASES.md
+++ b/RELEASES.md
@@ -17,6 +17,7 @@ Breaking changes
 Bug fixes
 ---------
 
+* Parameters passed to plugin module functions were sometimes erroneously consumed. This is now fixed.
 * Fixes compilation errors in `metadata` feature build.
 
 New features
diff --git a/src/fn_call.rs b/src/fn_call.rs
index 929eb825..7e277d77 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -1210,16 +1210,18 @@ impl Engine {
             r => r,
         };
 
+        // Clone first argument if the function is not a method after-all
+        if let Some(first) = first_arg_value {
+            if !func.map(|f| f.is_method()).unwrap_or(true) {
+                let first_val = args[0].clone();
+                args[0] = first;
+                *args[0] = first_val;
+            }
+        }
+
         match func {
             #[cfg(not(feature = "no_function"))]
             Some(f) if f.is_script() => {
-                // Clone first argument
-                if let Some(first) = first_arg_value {
-                    let first_val = args[0].clone();
-                    args[0] = first;
-                    *args[0] = first_val;
-                }
-
                 let args = args.as_mut();
                 let new_scope = &mut Default::default();
                 let fn_def = f.get_fn_def().clone();
@@ -1241,21 +1243,10 @@ impl Engine {
                 (self, fn_name, module.id(), &*mods, lib).into(),
                 args.as_mut(),
             ),
-            Some(f) if f.is_native() => {
-                if !f.is_method() {
-                    // Clone first argument
-                    if let Some(first) = first_arg_value {
-                        let first_val = args[0].clone();
-                        args[0] = first;
-                        *args[0] = first_val;
-                    }
-                }
-
-                f.get_native_fn()(
-                    (self, fn_name, module.id(), &*mods, lib).into(),
-                    args.as_mut(),
-                )
-            }
+            Some(f) if f.is_native() => f.get_native_fn()(
+                (self, fn_name, module.id(), &*mods, lib).into(),
+                args.as_mut(),
+            ),
             Some(f) => unreachable!("unknown function type: {:?}", f),
             None if def_val.is_some() => Ok(def_val.unwrap().clone()),
             None => EvalAltResult::ErrorFunctionNotFound(
diff --git a/tests/plugins.rs b/tests/plugins.rs
index 4ba79f6f..e42c4c73 100644
--- a/tests/plugins.rs
+++ b/tests/plugins.rs
@@ -101,3 +101,32 @@ fn test_plugins_package() -> Result<(), Box<EvalAltResult>> {
 
     Ok(())
 }
+
+#[test]
+fn test_plugins_parameters() -> Result<(), Box<EvalAltResult>> {
+    #[export_module]
+    mod rhai_std {
+        use rhai::*;
+
+        pub fn noop(_: &str) {}
+    }
+
+    let mut engine = Engine::new();
+
+    let std = exported_module!(rhai_std);
+
+    engine.register_static_module("std", std.into());
+
+    assert_eq!(
+        engine.eval::<String>(
+            r#"
+                let s = "hello";
+                std::noop(s);
+                s
+            "#
+        )?,
+        "hello"
+    );
+
+    Ok(())
+}