Apply defaults to invokes (#142)

Fixes #115 

This change applies default values as part of `Invoke`. This is inline
with the behavior for resources.

infer/function.go

@@ -133,6 +133,12 @@ func (r *derivedInvokeController[F, I, O]) Invoke(ctx p.Context, req p.InvokeReq
 			Failures: mapFailures,
 		}, nil
 	}
+
+	err = applyDefaults(&i)
+	if err != nil {
+		return p.InvokeResponse{}, fmt.Errorf("unable to apply defaults: %w", err)
+	}
+
 	var f F
 	// If F is a *struct, we need to rehydrate the underlying struct
 	if v := reflect.ValueOf(f); v.Kind() == reflect.Pointer && v.IsNil() {

infer/tests/invoke_test.go

@@ -0,0 +1,105 @@
+// Copyright 2022, Pulumi Corporation.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tests
+
+import (
+	"testing"
+
+	"github.com/pulumi/pulumi/sdk/v3/go/common/resource"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	p "github.com/pulumi/pulumi-go-provider"
+)
+
+func TestInvoke(t *testing.T) {
+	t.Parallel()
+	pString := resource.NewStringProperty
+	type pMap = resource.PropertyMap
+	type pValue = resource.PropertyValue
+
+	t.Run("missing-arg", func(t *testing.T) {
+		t.Parallel()
+		prov := provider()
+		resp, err := prov.Invoke(p.InvokeRequest{
+			Token: "test:index:getJoin",
+			Args:  pMap{},
+		})
+		require.NoError(t, err)
+		assert.Equal(t, 1, len(resp.Failures)) // Missing required field `elems`
+	})
+
+	t.Run("all-args", func(t *testing.T) {
+		t.Parallel()
+		prov := provider()
+		resp, err := prov.Invoke(p.InvokeRequest{
+			Token: "test:index:getJoin",
+			Args: pMap{
+				"elems": pValue{V: []pValue{
+					pString("foo"),
+					pString("bar"),
+				}},
+				"sep": pString("-"),
+			},
+		})
+		require.NoError(t, err)
+		assert.Empty(t, resp.Failures)
+
+		assert.Equal(t, pMap{
+			"result": pString("foo-bar"),
+		}, resp.Return)
+	})
+
+	t.Run("default-args", func(t *testing.T) {
+		t.Parallel()
+		prov := provider()
+		resp, err := prov.Invoke(p.InvokeRequest{
+			Token: "test:index:getJoin",
+			Args: pMap{
+				"elems": pValue{V: []pValue{
+					pString("foo"),
+					pString("bar"),
+				}},
+			},
+		})
+		require.NoError(t, err)
+		assert.Empty(t, resp.Failures)
+
+		assert.Equal(t, pMap{
+			"result": pString("foo,bar"), // default value is ","
+		}, resp.Return)
+	})
+	t.Run("zero-args", func(t *testing.T) {
+		t.Parallel()
+		prov := provider()
+		resp, err := prov.Invoke(p.InvokeRequest{
+			Token: "test:index:getJoin",
+			Args: pMap{
+				"elems": pValue{V: []pValue{
+					pString("foo"),
+					pString("bar"),
+				}},
+				"sep": pString(""),
+			},
+		})
+		require.NoError(t, err)
+		assert.Empty(t, resp.Failures)
+
+		assert.Equal(t, pMap{
+			"result": pString("foobar"), // The default doesn't apply here
+		}, resp.Return)
+	})
+
+}

infer/tests/provider.go

@@ -17,6 +17,7 @@ package tests
 import (
 	"encoding/json"
 	"fmt"
+	"strings"
 
 	"github.com/blang/semver"
 	"github.com/pulumi/pulumi/sdk/v3/go/common/resource"
@@ -321,6 +322,24 @@ func (w *ReadConfig) Create(
 	return "read", ReadConfigOutput{Config: string(bytes)}, err
 }
 
+type GetJoin struct{}
+type JoinArgs struct {
+	Elems []string `pulumi:"elems"`
+	Sep   *string  `pulumi:"sep,optional"`
+}
+
+func (j *JoinArgs) Annotate(a infer.Annotator) {
+	a.SetDefault(&j.Sep, ",")
+}
+
+type JoinResult struct {
+	Result string `pulumi:"result"`
+}
+
+func (*GetJoin) Call(ctx p.Context, args JoinArgs) (JoinResult, error) {
+	return JoinResult{strings.Join(args.Elems, *args.Sep)}, nil
+}
+
 type ConfigCustom struct {
 	Number  *float64 `pulumi:"number,optional"`
 	Squared float64
@@ -380,6 +399,9 @@ func providerOpts(config infer.InferredConfig) infer.Options {
 			infer.Resource[*ReadConfig, ReadConfigArgs, ReadConfigOutput](),
 			infer.Resource[*ReadConfigCustom, ReadConfigCustomArgs, ReadConfigCustomOutput](),
 		},
+		Functions: []infer.InferredFunction{
+			infer.Function[*GetJoin, JoinArgs, JoinResult](),
+		},
 		ModuleMap: map[tokens.ModuleName]tokens.ModuleName{"tests": "index"},
 	}
 }