cmd/wire: add a --header_file flag to the "gen" and "diff" commands (#175)

internal/wire/testdata/Header/foo/foo.go

@@ -0,0 +1,29 @@
+// Copyright 2019 The Wire Authors
+//
+// 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"
+)
+
+func main() {
+	fmt.Println(injectFoo())
+}
+
+type Foo int
+
+func provideFoo() Foo {
+	return 41
+}

internal/wire/testdata/Header/foo/wire.go

@@ -0,0 +1,26 @@
+// Copyright 2019 The Wire Authors
+//
+// 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/wire"
+)
+
+func injectFoo() Foo {
+	wire.Build(provideFoo)
+	return Foo(0)
+}

internal/wire/testdata/Header/header

@@ -0,0 +1,2 @@
+// This is a sample header file.
+//

internal/wire/testdata/Header/pkg

@@ -0,0 +1 @@
+example.com/foo

internal/wire/testdata/Header/want/program_out.txt

@@ -0,0 +1 @@
+41

internal/wire/testdata/Header/want/wire_gen.go

@@ -0,0 +1,15 @@
+// This is a sample header file.
+//
+// Code generated by Wire. DO NOT EDIT.
+
+//go:generate wire
+//+build !wireinject
+
+package main
+
+// Injectors from wire.go:
+
+func injectFoo() Foo {
+	foo := provideFoo()
+	return foo
+}