internal/wire: factor out common code in solve (#98)

- Fixed a bug when a interface is bind to a value wire would fail to record it is used.
- Also rename ProvidedType.ConcreteType to Type since it doesn't necessarily returns a concrete type.

Fixes #72

internal/wire/testdata/BindInterfaceWithValue/foo/foo.go

@@ -0,0 +1,20 @@
+// Copyright 2018 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
+
+func main() {
+	w := inject()
+	w.Write([]byte("Hello, World!"))
+}

internal/wire/testdata/BindInterfaceWithValue/foo/wire.go

@@ -0,0 +1,32 @@
+// Copyright 2018 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 (
+	"io"
+	"os"
+
+	"github.com/google/wire"
+)
+
+func inject() io.Writer {
+	wire.Build(
+		wire.Value(os.Stdout),
+		wire.Bind(new(io.Writer), new(os.File)),
+	)
+	return nil
+}

internal/wire/testdata/BindInterfaceWithValue/pkg

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

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

@@ -0,0 +1 @@
+Hello, World!

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

@@ -0,0 +1,22 @@
+// Code generated by Wire. DO NOT EDIT.
+
+//go:generate wire
+//+build !wireinject
+
+package main
+
+import (
+	"io"
+	"os"
+)
+
+// Injectors from wire.go:
+
+func inject() io.Writer {
+	file := _wireFileValue
+	return file
+}
+
+var (
+	_wireFileValue = os.Stdout
+)