ext/wasm: Check exit code on returned error (#2223)

As part of migrating plugins to the official Go toolchain, the wasmtime
call pattern needed to be updated. This should be backwards compatible
with TinyGo plugins.

Author: kyleconroy

internal/ext/wasm/wasm.go

@@ -258,32 +258,54 @@ func (r *Runner) Generate(ctx context.Context, req *plugin.CodeGenRequest) (*plu
 	store := wasmtime.NewStore(engine)
 	store.SetWasi(wasiConfig)
 
-	linkRegion := trace.StartRegion(ctx, "linker.Instantiate")
-	instance, err := linker.Instantiate(store, module)
+	linkRegion := trace.StartRegion(ctx, "linker.DefineModule")
+	err = linker.DefineModule(store, "", module)
 	linkRegion.End()
 	if err != nil {
 		return nil, fmt.Errorf("define wasi: %w", err)
 	}
 
 	// Run the function
+	fn, err := linker.GetDefault(store, "")
+	if err != nil {
+		return nil, fmt.Errorf("wasi: get default: %w", err)
+	}
+
 	callRegion := trace.StartRegion(ctx, "call _start")
-	nom := instance.GetExport(store, "_start").Func()
-	_, err = nom.Call(store)
+	_, err = fn.Call(store)
 	callRegion.End()
-	if err != nil {
-		// Print WASM stdout
-		stderrBlob, err := os.ReadFile(stderrPath)
-		if err == nil && len(stderrBlob) > 0 {
-			return nil, errors.New(string(stderrBlob))
-		}
-		return nil, fmt.Errorf("call: %w", err)
+
+	if cerr := checkError(err, stderrPath); cerr != nil {
+		return nil, cerr
 	}
 
 	// Print WASM stdout
 	stdoutBlob, err := os.ReadFile(stdoutPath)
 	if err != nil {
 		return nil, fmt.Errorf("read file: %w", err)
 	}
+
 	var resp plugin.CodeGenResponse
 	return &resp, resp.UnmarshalVT(stdoutBlob)
 }
+
+func checkError(err error, stderrPath string) error {
+	if err == nil {
+		return err
+	}
+
+	var wtError *wasmtime.Error
+	if errors.As(err, &wtError) {
+		if code, ok := wtError.ExitStatus(); ok {
+			if code == 0 {
+				return nil
+			}
+		}
+	}
+	// Print WASM stdout
+	stderrBlob, rferr := os.ReadFile(stderrPath)
+	if rferr == nil && len(stderrBlob) > 0 {
+		return errors.New(string(stderrBlob))
+	}
+	return fmt.Errorf("call: %w", err)
+}