Restores ModuleConfig.WithName to support cloned Wasm (#282)

PR #281 allowed repetitive use of the same module config to avoid
re-decoding the same wasm. However, it is possible that configuration is
renamed in separate goroutines. This makes caching safer by restoring
the `WithName` function deleted earlier. By using this, a configuration
and its cache state are cloned, and doing that is thread safe.

Signed-off-by: Adrian Cole <[email protected]>

wasm.go

@@ -78,6 +78,16 @@ func (m *ModuleConfig) Validate() (err error) {
 	return err
 }
 
+// WithName returns a new instance which overrides the Name, but keeps any internal cache made by Validate.
+func (m *ModuleConfig) WithName(moduleName string) *ModuleConfig {
+	return &ModuleConfig{
+		Name:            moduleName,
+		Source:          m.Source,
+		validatedSource: m.validatedSource,
+		decodedModule:   m.decodedModule,
+	}
+}
+
 // InstantiateModule instantiates the module namespace or errs if the configuration was invalid.
 //
 // Ex.

wasm_test.go

@@ -55,21 +55,32 @@ func TestDecodeModule(t *testing.T) {
 
 		again, _, err := decodeModule(config)
 		require.NoError(t, err)
-
 		require.Same(t, m, again)
+
+		// Ensure config that only changes the name doesn't have to re-decode the source.
+		cloned, _, err := decodeModule(config.WithName("wazero"))
+		require.NoError(t, err)
+		require.Same(t, m, cloned)
 	})
 
 	t.Run("changing source invalidates decode cache", func(t *testing.T) {
 		config := &ModuleConfig{Source: wat}
 		m, _, err := decodeModule(config)
 		require.NoError(t, err)
 
+		clonedConfig := config.WithName("wazero")
+
+		// When the source is changed, the module needs to be decoded again
 		config.Source = wasm
 		again, _, err := decodeModule(config)
 		require.NoError(t, err)
-
 		require.Equal(t, m, again)
 		require.NotSame(t, m, again)
+
+		// Any copies of the config shouldn't be invalidated
+		cloned, _, err := decodeModule(clonedConfig)
+		require.NoError(t, err)
+		require.Same(t, m, cloned)
 	})
 }