Improve diagonstics on return_raw return mismatches

codegen/ui_tests/export_fn_raw_noreturn.rs

@@ -0,0 +1,25 @@
+use rhai::plugin::*;
+
+#[derive(Clone)]
+struct Point {
+    x: f32,
+    y: f32,
+}
+
+#[export_fn(return_raw)]
+pub fn test_fn(input: &mut Point) {
+    input.x += 1.0;
+}
+
+fn main() {
+    let n = Point {
+        x: 0.0,
+        y: 10.0,
+    };
+    test_fn(&mut n);
+    if n.x >= 10.0 {
+        println!("yes");
+    } else {
+        println!("no");
+    }
+}

codegen/ui_tests/export_fn_raw_noreturn.stderr

@@ -0,0 +1,11 @@
+error: return_raw functions must return Result<T>
+  --> $DIR/export_fn_raw_noreturn.rs:10:5
+   |
+10 | pub fn test_fn(input: &mut Point) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0425]: cannot find function `test_fn` in this scope
+  --> $DIR/export_fn_raw_noreturn.rs:19:5
+   |
+19 |     test_fn(&mut n);
+   |     ^^^^^^^ not found in this scope

codegen/ui_tests/export_fn_raw_return.rs

@@ -0,0 +1,24 @@
+use rhai::plugin::*;
+
+#[derive(Clone)]
+struct Point {
+    x: f32,
+    y: f32,
+}
+
+#[export_fn(return_raw)]
+pub fn test_fn(input: Point) -> bool {
+    input.x > input.y
+}
+
+fn main() {
+    let n = Point {
+        x: 0.0,
+        y: 10.0,
+    };
+    if test_fn(n) {
+        println!("yes");
+    } else {
+        println!("no");
+    }
+}

codegen/ui_tests/export_fn_raw_return.stderr

@@ -0,0 +1,21 @@
+error[E0308]: mismatched types
+  --> $DIR/export_fn_raw_return.rs:10:8
+   |
+9  | #[export_fn(return_raw)]
+   | ------------------------ expected `std::result::Result<rhai::Dynamic, std::boxed::Box<rhai::EvalAltResult>>` because of return type
+10 | pub fn test_fn(input: Point) -> bool {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected enum `std::result::Result`, found `bool`
+   |
+   = note: expected enum `std::result::Result<rhai::Dynamic, std::boxed::Box<rhai::EvalAltResult>>`
+              found type `bool`
+
+error[E0308]: mismatched types
+  --> $DIR/export_fn_raw_return.rs:10:33
+   |
+9  | #[export_fn(return_raw)]
+   | ------------------------ expected `std::result::Result<rhai::Dynamic, std::boxed::Box<rhai::EvalAltResult>>` because of return type
+10 | pub fn test_fn(input: Point) -> bool {
+   |                                 ^^^^ expected enum `std::result::Result`, found `bool`
+   |
+   = note: expected enum `std::result::Result<rhai::Dynamic, std::boxed::Box<rhai::EvalAltResult>>`
+              found type `bool`