wire: Build now returns an error if it has any unused arguments (google/go-cloud#268)

Fixes google/go-cloud#164

internal/wire/testdata/UnusedProviders/foo/foo.go

@@ -0,0 +1,71 @@
+// Copyright 2018 Google LLC
+//
+// 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
+//
+//     https://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 main
+
+import (
+	"fmt"
+
+	"github.com/google/go-cloud/wire"
+)
+
+func main() {
+	fmt.Println(injectBar())
+}
+
+type Foo int
+type Bar int
+type Unused int
+type UnusedInSet int
+type OneOfTwo int
+type TwoOfTwo int
+
+var (
+	unusedSet        = wire.NewSet(provideUnusedInSet)
+	partiallyUsedSet = wire.NewSet(provideOneOfTwo, provideTwoOfTwo)
+)
+
+type Fooer interface {
+	Foo() string
+}
+
+func (f *Foo) Foo() string {
+	return fmt.Sprintf("Hello World %d", f)
+}
+
+func provideFoo() *Foo {
+	f := new(Foo)
+	*f = 1
+	return f
+}
+
+func provideBar(foo *Foo, one OneOfTwo) Bar {
+	return Bar(int(*foo) + int(one))
+}
+
+func provideUnused() Unused {
+	return 1
+}
+
+func provideUnusedInSet() UnusedInSet {
+	return 1
+}
+
+func provideOneOfTwo() OneOfTwo {
+	return 1
+}
+
+func provideTwoOfTwo() TwoOfTwo {
+	return 1
+}

internal/wire/testdata/UnusedProviders/foo/wire.go

@@ -0,0 +1,34 @@
+// Copyright 2018 Google LLC
+//
+// 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
+//
+//     https://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.
+
+//+build wireinject
+
+package main
+
+import (
+	"github.com/google/go-cloud/wire"
+)
+
+func injectBar() Bar {
+	wire.Build(
+		provideFoo,                            // needed as input for provideBar
+		provideBar,                            // needed for Bar
+		partiallyUsedSet,                      // 1/2 providers in the set are needed
+		provideUnused,                         // not needed -> error
+		wire.Value("unused"),                  // not needed -> error
+		unusedSet,                             // nothing in set is needed -> error
+		wire.Bind((*Fooer)(nil), (*Foo)(nil)), // binding to Fooer is not needed -> error
+	)
+	return 0
+}

internal/wire/testdata/UnusedProviders/out.txt

@@ -0,0 +1,5 @@
+ERROR
+unused provider set
+unused provider "provideUnused"
+unused value of type string
+unused interface binding to type foo.Fooer

internal/wire/testdata/UnusedProviders/pkg

@@ -0,0 +1 @@
+foo