Merge #38

38: fix(instance) Handle exported functions that return nothing r=Hywan a=Hywan

WebAssembly “void” is mapped to `None` in Python.

Co-authored-by: Ivan Enderlin <ivan.enderlin@hoa-project.net>

README.md

@@ -85,7 +85,7 @@ from wasmer import Instance
 # Get the Wasm module as bytes.
 wasm_bytes = open('my_program.wasm', 'rb').read()
 
-# Instantiates the Wasm module.
+# Instantiate the Wasm module.
 instance = Instance(wasm_bytes)
 
 # Call a function on it.
@@ -193,7 +193,7 @@ from wasmer import Instance
 # Get the Wasm module as bytes.
 wasm_bytes = open('my_program.wasm', 'rb').read()
 
-# Instantiates the Wasm module.
+# Instantiate the Wasm module.
 instance = Instance(wasm_bytes)
 
 # Call a function that returns a pointer to a string for instance.

src/instance.rs

@@ -111,12 +111,16 @@ impl ExportedFunction {
         };
 
         // Map the WebAssembly first result to a Python value.
-        Ok(match results[0] {
-            WasmValue::I32(result) => result.to_object(py),
-            WasmValue::I64(result) => result.to_object(py),
-            WasmValue::F32(result) => result.to_object(py),
-            WasmValue::F64(result) => result.to_object(py),
-        })
+        if results.len() > 0 {
+            Ok(match results[0] {
+                WasmValue::I32(result) => result.to_object(py),
+                WasmValue::I64(result) => result.to_object(py),
+                WasmValue::F32(result) => result.to_object(py),
+                WasmValue::F64(result) => result.to_object(py),
+            })
+        } else {
+            Ok(py.None())
+        }
     }
 }
 

tests/test_instance.py

@@ -65,6 +65,9 @@ def test_call_bool_casted_to_i32():
 def test_call_string():
     assert Instance(TEST_BYTES).exports.string() == 1048576
 
+def test_call_void():
+    assert Instance(TEST_BYTES).exports.void() == None
+
 def test_validate():
     assert validate(TEST_BYTES)
 

tests/tests.rs

@@ -42,3 +42,6 @@ pub extern fn bool_casted_to_i32() -> bool {
 pub extern fn string() -> *const u8 {
     b"Hello, World!\0".as_ptr()
 }
+
+#[no_mangle]
+pub extern fn void() {}