add FieldsOf to inject fields of a struct directly (#138)

internal/wire/analyze.go

@@ -32,6 +32,7 @@ const (
 	funcProviderCall callKind = iota
 	structProvider
 	valueExpr
+	selectorExpr
 )
 
 // A call represents a step of an injector function.  It may be either a
@@ -44,17 +45,21 @@ type call struct {
 	// out is the type this step produces.
 	out types.Type
 
-	// pkg and name identify the provider to call for kind ==
-	// funcProviderCall or the type to construct for kind ==
-	// structProvider.
+	// pkg and name identify one of the following:
+	// 1) the provider to call for kind == funcProviderCall;
+	// 2) the type to construct for kind == structProvider;
+	// 3) the name to select for kind == selectorExpr.
 	pkg  *types.Package
 	name string
 
-	// args is a list of arguments to call the provider with.  Each element is:
-	// a) one of the givens (args[i] < len(given)), or
+	// args is a list of arguments to call the provider with. Each element is:
+	// a) one of the givens (args[i] < len(given)),
 	// b) the result of a previous provider call (args[i] >= len(given))
 	//
 	// This will be nil for kind == valueExpr.
+	//
+	// If kind == selectorExpr, then the length of this slice will be 1 and the
+	// "argument" will be the value to access fields from.
 	args []int
 
 	// varargs is true if the provider function is variadic.
@@ -207,6 +212,29 @@ dfs:
 				valueExpr:     v.expr,
 				valueTypeInfo: v.info,
 			})
+		case pv.IsField():
+			f := pv.Field()
+			if index.At(f.Parent) == nil {
+				// Fields have one dependency which is the parent struct. Make
+				// sure to visit it first if it is not already visited.
+				stk = append(stk, curr, frame{t: f.Parent, from: curr.t, up: &curr})
+				continue
+			}
+			index.Set(curr.t, given.Len()+len(calls))
+			v := index.At(f.Parent)
+			if v == errAbort {
+				index.Set(curr.t, errAbort)
+				continue dfs
+			}
+			// Use the args[0] to store the position of the parent struct.
+			args := []int{v.(int)}
+			calls = append(calls, call{
+				kind: selectorExpr,
+				pkg:  f.Pkg,
+				name: f.Name,
+				out:  curr.t,
+				args: args,
+			})
 		default:
 			panic("unknown return value from ProviderSet.For")
 		}
@@ -275,11 +303,24 @@ func verifyArgsUsed(set *ProviderSet, used []*providerSetSrc) []error {
 			errs = append(errs, fmt.Errorf("unused interface binding to type %s", types.TypeString(b.Iface, nil)))
 		}
 	}
+	for _, f := range set.Fields {
+		found := false
+		for _, u := range used {
+			if u.Field == f {
+				found = true
+				break
+			}
+		}
+		if !found {
+			errs = append(errs, fmt.Errorf("unused field %q.%s", f.Parent, f.Name))
+		}
+	}
 	return errs
 }
 
-// buildProviderMap creates the providerMap and srcMap fields for a given provider set.
-// The given provider set's providerMap and srcMap fields are ignored.
+// buildProviderMap creates the providerMap and srcMap fields for a given
+// provider set. The given provider set's providerMap and srcMap fields are
+// ignored.
 func buildProviderMap(fset *token.FileSet, hasher typeutil.Hasher, set *ProviderSet) (*typeutil.Map, *typeutil.Map, []error) {
 	providerMap := new(typeutil.Map)
 	providerMap.SetHasher(hasher)
@@ -339,6 +380,15 @@ func buildProviderMap(fset *token.FileSet, hasher typeutil.Hasher, set *Provider
 		providerMap.Set(v.Out, &ProvidedType{t: v.Out, v: v})
 		srcMap.Set(v.Out, src)
 	}
+	for _, f := range set.Fields {
+		src := &providerSetSrc{Field: f}
+		if prevSrc := srcMap.At(f.Out); prevSrc != nil {
+			ec.add(bindingConflictError(fset, f.Out, set, src, prevSrc.(*providerSetSrc)))
+			continue
+		}
+		providerMap.Set(f.Out, &ProvidedType{t: f.Out, f: f})
+		srcMap.Set(f.Out, src)
+	}
 	if len(ec.errors) > 0 {
 		return nil, nil, ec.errors
 	}
@@ -398,38 +448,49 @@ func verifyAcyclic(providerMap *typeutil.Map, hasher typeutil.Hasher) []error {
 				continue
 			}
 			pt := x.(*ProvidedType)
-			if pt.IsValue() {
+			switch {
+			case pt.IsValue():
 				// Leaf: values do not have dependencies.
-				continue
-			}
-			if pt.IsArg() {
+			case pt.IsArg():
 				// Injector arguments do not have dependencies.
-				continue
-			}
-			if !pt.IsProvider() {
-				panic("invalid provider map value")
-			}
-			for _, arg := range pt.Provider().Args {
-				a := arg.Type
-				hasCycle := false
-				for i, b := range curr {
-					if types.Identical(a, b) {
-						sb := new(strings.Builder)
-						fmt.Fprintf(sb, "cycle for %s:\n", types.TypeString(a, nil))
-						for j := i; j < len(curr); j++ {
-							p := providerMap.At(curr[j]).(*ProvidedType).Provider()
-							fmt.Fprintf(sb, "%s (%s.%s) ->\n", types.TypeString(curr[j], nil), p.Pkg.Path(), p.Name)
+			case pt.IsProvider() || pt.IsField():
+				var args []types.Type
+				if pt.IsProvider() {
+					for _, arg := range pt.Provider().Args {
+						args = append(args, arg.Type)
+					}
+				} else {
+					args = append(args, pt.Field().Parent)
+				}
+				for _, a := range args {
+					hasCycle := false
+					for i, b := range curr {
+						if types.Identical(a, b) {
+							sb := new(strings.Builder)
+							fmt.Fprintf(sb, "cycle for %s:\n", types.TypeString(a, nil))
+							for j := i; j < len(curr); j++ {
+								t := providerMap.At(curr[j]).(*ProvidedType)
+								if t.IsProvider() {
+									p := t.Provider()
+									fmt.Fprintf(sb, "%s (%s.%s) ->\n", types.TypeString(curr[j], nil), p.Pkg.Path(), p.Name)
+								} else {
+									p := t.Field()
+									fmt.Fprintf(sb, "%s (%s.%s) ->\n", types.TypeString(curr[j], nil), p.Parent, p.Name)
+								}
+							}
+							fmt.Fprintf(sb, "%s", types.TypeString(a, nil))
+							ec.add(errors.New(sb.String()))
+							hasCycle = true
+							break
 						}
-						fmt.Fprintf(sb, "%s", types.TypeString(a, nil))
-						ec.add(errors.New(sb.String()))
-						hasCycle = true
-						break
+					}
+					if !hasCycle {
+						next := append(append([]types.Type(nil), curr...), a)
+						stk = append(stk, next)
 					}
 				}
-				if !hasCycle {
-					next := append(append([]types.Type(nil), curr...), a)
-					stk = append(stk, next)
-				}
+			default:
+				panic("invalid provider map value")
 			}
 		}
 	}

internal/wire/parse.go

@@ -37,6 +37,7 @@ type providerSetSrc struct {
 	Value       *Value
 	Import      *ProviderSet
 	InjectorArg *InjectorArg
+	Field       *Field
 }
 
 // description returns a string describing the source of p, including line numbers.
@@ -63,6 +64,8 @@ func (p *providerSetSrc) description(fset *token.FileSet, typ types.Type) string
 	case p.InjectorArg != nil:
 		args := p.InjectorArg.Args
 		return fmt.Sprintf("argument %s to injector function %s (%s)", args.Tuple.At(p.InjectorArg.Index).Name(), args.Name, fset.Position(args.Pos))
+	case p.Field != nil:
+		return fmt.Sprintf("wire.FieldsOf (%s)", fset.Position(p.Field.Pos))
 	}
 	panic("providerSetSrc with no fields set")
 }
@@ -96,6 +99,7 @@ type ProviderSet struct {
 	Providers []*Provider
 	Bindings  []*IfaceBinding
 	Values    []*Value
+	Fields    []*Field
 	Imports   []*ProviderSet
 	// InjectorArgs is only filled in for wire.Build.
 	InjectorArgs *InjectorArgs
@@ -214,6 +218,21 @@ type InjectorArgs struct {
 	Pos token.Pos
 }
 
+// Field describes a list of fields from a struct.
+type Field struct {
+	// Parent is the struct or pointer to the struct that the field belongs to.
+	Parent types.Type
+	// Name is the field name.
+	Name string
+	// Pkg is the package that the struct resides in.
+	Pkg *types.Package
+	// Pos is the source position of the field declaration.
+	// defining these fields.
+	Pos token.Pos
+	// Out is the field's type.
+	Out types.Type
+}
+
 // Load finds all the provider sets in the packages that match the given
 // patterns, as well as the provider sets' transitive dependencies. It
 // may return both errors and Info. The patterns are defined by the
@@ -436,8 +455,8 @@ func newObjectCache(pkgs []*packages.Package) *objectCache {
 	return oc
 }
 
-// get converts a Go object into a Wire structure. It may return a
-// *Provider, an *IfaceBinding, a *ProviderSet, or a *Value.
+// get converts a Go object into a Wire structure. It may return a *Provider, an
+// *IfaceBinding, a *ProviderSet, a *Value, or a *Fields.
 func (oc *objectCache) get(obj types.Object) (val interface{}, errs []error) {
 	ref := objRef{
 		importPath: obj.Pkg().Path(),
@@ -493,8 +512,8 @@ func (oc *objectCache) varDecl(obj *types.Var) *ast.ValueSpec {
 	return nil
 }
 
-// processExpr converts an expression into a Wire structure. It may
-// return a *Provider, an *IfaceBinding, a *ProviderSet, or a *Value.
+// processExpr converts an expression into a Wire structure. It may return a
+// *Provider, an *IfaceBinding, a *ProviderSet, a *Value or a *Field.
 func (oc *objectCache) processExpr(info *types.Info, pkgPath string, expr ast.Expr, varName string) (interface{}, []error) {
 	exprPos := oc.fset.Position(expr.Pos())
 	expr = astutil.Unparen(expr)
@@ -531,6 +550,12 @@ func (oc *objectCache) processExpr(info *types.Info, pkgPath string, expr ast.Ex
 				return nil, []error{notePosition(exprPos, err)}
 			}
 			return v, nil
+		case "FieldsOf":
+			v, err := processFieldsOf(oc.fset, info, call)
+			if err != nil {
+				return nil, []error{notePosition(exprPos, err)}
+			}
+			return v, nil
 		default:
 			return nil, []error{notePosition(exprPos, errors.New("unknown pattern"))}
 		}
@@ -570,6 +595,8 @@ func (oc *objectCache) processNewSet(info *types.Info, pkgPath string, call *ast
 			pset.Bindings = append(pset.Bindings, item)
 		case *Value:
 			pset.Values = append(pset.Values, item)
+		case []*Field:
+			pset.Fields = append(pset.Fields, item...)
 		default:
 			panic("unknown item type")
 		}
@@ -845,6 +872,73 @@ func processInterfaceValue(fset *token.FileSet, info *types.Info, call *ast.Call
 	}, nil
 }
 
+// processFieldsOf creates a list of fields from a wire.FieldsOf call.
+func processFieldsOf(fset *token.FileSet, info *types.Info, call *ast.CallExpr) ([]*Field, error) {
+	// Assumes that call.Fun is wire.FieldsOf.
+
+	if len(call.Args) < 2 {
+		return nil, notePosition(fset.Position(call.Pos()),
+			errors.New("call to FieldsOf must specify fields to be extracted"))
+	}
+	const firstArgReqFormat = "first argument to FieldsOf must be a pointer to a struct or a pointer to a pointer to a struct; found %s"
+	structType := info.TypeOf(call.Args[0])
+	structPtr, ok := structType.(*types.Pointer)
+	if !ok {
+		return nil, notePosition(fset.Position(call.Pos()),
+			fmt.Errorf(firstArgReqFormat, types.TypeString(structType, nil)))
+	}
+
+	var struc *types.Struct
+	switch t := structPtr.Elem().Underlying().(type) {
+	case *types.Pointer:
+		struc, ok = t.Elem().Underlying().(*types.Struct)
+		if !ok {
+			return nil, notePosition(fset.Position(call.Pos()),
+				fmt.Errorf(firstArgReqFormat, types.TypeString(struc, nil)))
+		}
+	case *types.Struct:
+		struc = t
+	default:
+		return nil, notePosition(fset.Position(call.Pos()),
+			fmt.Errorf(firstArgReqFormat, types.TypeString(t, nil)))
+	}
+	if struc.NumFields() < len(call.Args)-1 {
+		return nil, notePosition(fset.Position(call.Pos()),
+			fmt.Errorf("fields number exceeds the number available in the struct which has %d fields", struc.NumFields()))
+	}
+
+	fields := make([]*Field, 0, len(call.Args)-1)
+	for i := 1; i < len(call.Args); i++ {
+		v, err := checkField(call.Args[i], struc)
+		if err != nil {
+			return nil, notePosition(fset.Position(call.Pos()), err)
+		}
+		fields = append(fields, &Field{
+			Parent: structPtr.Elem(),
+			Name:   v.Name(),
+			Pkg:    v.Pkg(),
+			Pos:    v.Pos(),
+			Out:    v.Type(),
+		})
+	}
+	return fields, nil
+}
+
+// checkField reports whether f is a field of st. f should be a string with the
+// field name.
+func checkField(f ast.Expr, st *types.Struct) (*types.Var, error) {
+	b, ok := f.(*ast.BasicLit)
+	if !ok {
+		return nil, fmt.Errorf("%v must be a string with the field name", f)
+	}
+	for i := 0; i < st.NumFields(); i++ {
+		if strings.EqualFold(strconv.Quote(st.Field(i).Name()), b.Value) {
+			return st.Field(i), nil
+		}
+	}
+	return nil, fmt.Errorf("%s is not a field of %s", b.Value, st.String())
+}
+
 // findInjectorBuild returns the wire.Build call if fn is an injector template.
 // It returns nil if the function is not an injector template.
 func findInjectorBuild(info *types.Info, fn *ast.FuncDecl) (*ast.CallExpr, error) {
@@ -928,11 +1022,12 @@ type ProvidedType struct {
 	p *Provider
 	v *Value
 	a *InjectorArg
+	f *Field
 }
 
 // IsNil reports whether pt is the zero value.
 func (pt ProvidedType) IsNil() bool {
-	return pt.p == nil && pt.v == nil && pt.a == nil
+	return pt.p == nil && pt.v == nil && pt.a == nil && pt.f == nil
 }
 
 // Type returns the output type.
@@ -961,6 +1056,11 @@ func (pt ProvidedType) IsArg() bool {
 	return pt.a != nil
 }
 
+// IsField reports whether pt points to a Fields.
+func (pt ProvidedType) IsField() bool {
+	return pt.f != nil
+}
+
 // Provider returns pt as a Provider pointer. It panics if pt does not point
 // to a Provider.
 func (pt ProvidedType) Provider() *Provider {
@@ -987,3 +1087,12 @@ func (pt ProvidedType) Arg() *InjectorArg {
 	}
 	return pt.a
 }
+
+// Field returns pt as a Field pointer. It panics if pt does not point to a
+// struct Field.
+func (pt ProvidedType) Field() *Field {
+	if pt.f == nil {
+		panic("ProvidedType does not hold a Field")
+	}
+	return pt.f
+}

internal/wire/testdata/FieldsOfCycle/foo/foo.go

@@ -0,0 +1,38 @@
+// 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(injectedBaz())
+}
+
+type Foo int
+type Baz int
+
+type Bar struct {
+	Bz Baz
+}
+
+func provideFoo(_ Baz) Foo {
+	return 0
+}
+
+func provideBar(_ Foo) Bar {
+	return Bar{}
+}

internal/wire/testdata/FieldsOfCycle/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 injectedBaz() Baz {
+	wire.Build(provideFoo, provideBar, wire.FieldsOf(new(Bar), "Bz"))
+	return 0
+}

internal/wire/testdata/FieldsOfCycle/pkg

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

internal/wire/testdata/FieldsOfCycle/want/wire_errs.txt

@@ -0,0 +1,5 @@
+example.com/foo/wire.go:x:y: cycle for example.com/foo.Bar:
+example.com/foo.Bar (example.com/foo.provideBar) ->
+example.com/foo.Foo (example.com/foo.provideFoo) ->
+example.com/foo.Baz (example.com/foo.Bar.Bz) ->
+example.com/foo.Bar

internal/wire/testdata/FieldsOfImportedStruct/bar/bar.go

@@ -0,0 +1,32 @@
+// 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 bar
+
+import (
+	"example.com/foo"
+)
+
+type Config struct {
+	V int
+}
+
+type Service struct {
+	Cfg *Config
+	F   *foo.Service
+}
+
+func New(cfg *Config, f *foo.Service) *Service {
+	return &Service{Cfg: cfg, F: f}
+}

internal/wire/testdata/FieldsOfImportedStruct/baz/baz.go

@@ -0,0 +1,36 @@
+// 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 baz
+
+import (
+	"fmt"
+
+	"example.com/bar"
+	"example.com/foo"
+)
+
+type Config struct {
+	Foo *foo.Config
+	Bar *bar.Config
+}
+
+type Service struct {
+	Foo *foo.Service
+	Bar *bar.Service
+}
+
+func (m *Service) String() string {
+	return fmt.Sprintf("%d %d", m.Foo.Cfg.V, m.Bar.Cfg.V)
+}

internal/wire/testdata/FieldsOfImportedStruct/foo/foo.go

@@ -0,0 +1,27 @@
+// 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 foo
+
+type Config struct {
+	V int
+}
+
+type Service struct {
+	Cfg *Config
+}
+
+func New(cfg *Config) *Service {
+	return &Service{Cfg: cfg}
+}

internal/wire/testdata/FieldsOfImportedStruct/main/wire.go

@@ -0,0 +1,49 @@
+// 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 (
+	"fmt"
+
+	"example.com/bar"
+	"example.com/baz"
+	"example.com/foo"
+	"github.com/google/wire"
+)
+
+func newBazService(*baz.Config) *baz.Service {
+	wire.Build(
+		baz.Service{},
+		wire.FieldsOf(
+			new(*baz.Config),
+			"Foo",
+			"Bar",
+		),
+		foo.New,
+		bar.New,
+	)
+	return nil
+}
+
+func main() {
+	cfg := &baz.Config{
+		Foo: &foo.Config{1},
+		Bar: &bar.Config{2},
+	}
+	svc := newBazService(cfg)
+	fmt.Println(svc.String())
+}

internal/wire/testdata/FieldsOfImportedStruct/pkg

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

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

@@ -0,0 +1 @@
+1 2

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

@@ -0,0 +1,38 @@
+// Code generated by Wire. DO NOT EDIT.
+
+//go:generate wire
+//+build !wireinject
+
+package main
+
+import (
+	"example.com/bar"
+	"example.com/baz"
+	"example.com/foo"
+	"fmt"
+)
+
+// Injectors from wire.go:
+
+func newBazService(config *baz.Config) *baz.Service {
+	fooConfig := config.Foo
+	service := foo.New(fooConfig)
+	barConfig := config.Bar
+	barService := bar.New(barConfig, service)
+	bazService := &baz.Service{
+		Foo: service,
+		Bar: barService,
+	}
+	return bazService
+}
+
+// wire.go:
+
+func main() {
+	cfg := &baz.Config{
+		Foo: &foo.Config{1},
+		Bar: &bar.Config{2},
+	}
+	svc := newBazService(cfg)
+	fmt.Println(svc.String())
+}

internal/wire/testdata/FieldsOfStruct/foo/foo.go

@@ -0,0 +1,29 @@
+// 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
+
+import "fmt"
+
+type S struct {
+	Foo string
+}
+
+func provideS() S {
+	return S{Foo: "Hello, World!"}
+}
+
+func main() {
+	fmt.Println(injectedMessage())
+}

internal/wire/testdata/FieldsOfStruct/foo/wire.go

@@ -0,0 +1,28 @@
+// 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 (
+	"github.com/google/wire"
+)
+
+func injectedMessage() string {
+	wire.Build(
+		provideS,
+		wire.FieldsOf(new(S), "Foo"))
+	return ""
+}

internal/wire/testdata/FieldsOfStruct/pkg

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

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

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

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

@@ -0,0 +1,14 @@
+// Code generated by Wire. DO NOT EDIT.
+
+//go:generate wire
+//+build !wireinject
+
+package main
+
+// Injectors from wire.go:
+
+func injectedMessage() string {
+	s := provideS()
+	string2 := s.Foo
+	return string2
+}

internal/wire/testdata/FieldsOfStructPointer/foo/foo.go

@@ -0,0 +1,29 @@
+// 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
+
+import "fmt"
+
+type S struct {
+	Foo string
+}
+
+func provideS() *S {
+	return &S{Foo: "Hello, World!"}
+}
+
+func main() {
+	fmt.Println(injectedMessage())
+}

internal/wire/testdata/FieldsOfStructPointer/foo/wire.go

@@ -0,0 +1,28 @@
+// 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 (
+	"github.com/google/wire"
+)
+
+func injectedMessage() string {
+	wire.Build(
+		provideS,
+		wire.FieldsOf(new(*S), "Foo"))
+	return ""
+}

internal/wire/testdata/FieldsOfStructPointer/pkg

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

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

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

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

@@ -0,0 +1,14 @@
+// Code generated by Wire. DO NOT EDIT.
+
+//go:generate wire
+//+build !wireinject
+
+package main
+
+// Injectors from wire.go:
+
+func injectedMessage() string {
+	s := provideS()
+	string2 := s.Foo
+	return string2
+}

internal/wire/testdata/FieldsOfValueStruct/bar/bar.go

@@ -0,0 +1,32 @@
+// 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 bar
+
+import (
+	"example.com/foo"
+)
+
+type Config struct {
+	V int
+}
+
+type Service struct {
+	Cfg *Config
+	F   *foo.Service
+}
+
+func New(cfg *Config, f *foo.Service) *Service {
+	return &Service{Cfg: cfg, F: f}
+}

internal/wire/testdata/FieldsOfValueStruct/baz/baz.go

@@ -0,0 +1,36 @@
+// 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 baz
+
+import (
+	"fmt"
+
+	"example.com/bar"
+	"example.com/foo"
+)
+
+type Config struct {
+	Foo *foo.Config
+	Bar *bar.Config
+}
+
+type Service struct {
+	Foo *foo.Service
+	Bar *bar.Service
+}
+
+func (m *Service) String() string {
+	return fmt.Sprintf("%d %d", m.Foo.Cfg.V, m.Bar.Cfg.V)
+}

internal/wire/testdata/FieldsOfValueStruct/foo/foo.go

@@ -0,0 +1,27 @@
+// 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 foo
+
+type Config struct {
+	V int
+}
+
+type Service struct {
+	Cfg *Config
+}
+
+func New(cfg *Config) *Service {
+	return &Service{Cfg: cfg}
+}

internal/wire/testdata/FieldsOfValueStruct/main/wire.go

@@ -0,0 +1,49 @@
+// 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 (
+	"fmt"
+
+	"example.com/bar"
+	"example.com/baz"
+	"example.com/foo"
+	"github.com/google/wire"
+)
+
+func newBazService() *baz.Service {
+	wire.Build(
+		baz.Service{},
+		wire.Value(&baz.Config{
+			Foo: &foo.Config{1},
+			Bar: &bar.Config{2},
+		}),
+		wire.FieldsOf(
+			new(*baz.Config),
+			"Foo",
+			"Bar",
+		),
+		foo.New,
+		bar.New,
+	)
+	return nil
+}
+
+func main() {
+	svc := newBazService()
+	fmt.Println(svc.String())
+}

internal/wire/testdata/FieldsOfValueStruct/pkg

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

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

@@ -0,0 +1 @@
+1 2

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

@@ -0,0 +1,42 @@
+// Code generated by Wire. DO NOT EDIT.
+
+//go:generate wire
+//+build !wireinject
+
+package main
+
+import (
+	"example.com/bar"
+	"example.com/baz"
+	"example.com/foo"
+	"fmt"
+)
+
+// Injectors from wire.go:
+
+func newBazService() *baz.Service {
+	config := _wireConfigValue
+	fooConfig := config.Foo
+	service := foo.New(fooConfig)
+	barConfig := config.Bar
+	barService := bar.New(barConfig, service)
+	bazService := &baz.Service{
+		Foo: service,
+		Bar: barService,
+	}
+	return bazService
+}
+
+var (
+	_wireConfigValue = &baz.Config{
+		Foo: &foo.Config{1},
+		Bar: &bar.Config{2},
+	}
+)
+
+// wire.go:
+
+func main() {
+	svc := newBazService()
+	fmt.Println(svc.String())
+}

internal/wire/testdata/MultipleSimilarPackages/main/wire.go

@@ -28,22 +28,28 @@ import (
 type MainConfig struct {
 	Foo *foo.Config
 	Bar *bar.Config
-	Baz *baz.Config
+	baz *baz.Config
 }
 
 type MainService struct {
 	Foo *foo.Service
 	Bar *bar.Service
-	Baz *baz.Service
+	baz *baz.Service
 }
 
 func (m *MainService) String() string {
-	return fmt.Sprintf("%d %d %d", m.Foo.Cfg.V, m.Bar.Cfg.V, m.Baz.Cfg.V)
+	return fmt.Sprintf("%d %d %d", m.Foo.Cfg.V, m.Bar.Cfg.V, m.baz.Cfg.V)
 }
 
-func newMainService(*foo.Config, *bar.Config, *baz.Config) *MainService {
+func newMainService(MainConfig) *MainService {
 	wire.Build(
 		MainService{},
+		wire.FieldsOf(
+			new(MainConfig),
+			"Foo",
+			"Bar",
+			"baz",
+		),
 		foo.New,
 		bar.New,
 		baz.New,
@@ -52,11 +58,11 @@ func newMainService(*foo.Config, *bar.Config, *baz.Config) *MainService {
 }
 
 func main() {
-	cfg := &MainConfig{
+	cfg := MainConfig{
 		Foo: &foo.Config{1},
 		Bar: &bar.Config{2},
-		Baz: &baz.Config{3},
+		baz: &baz.Config{3},
 	}
-	svc := newMainService(cfg.Foo, cfg.Bar, cfg.Baz)
+	svc := newMainService(cfg)
 	fmt.Println(svc.String())
 }

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

@@ -14,14 +14,17 @@ import (
 
 // Injectors from wire.go:
 
-func newMainService(config *foo.Config, barConfig *bar.Config, bazConfig *baz.Config) *MainService {
+func newMainService(mainConfig MainConfig) *MainService {
+	config := mainConfig.Foo
 	service := foo.New(config)
+	barConfig := mainConfig.Bar
 	barService := bar.New(barConfig, service)
+	bazConfig := mainConfig.baz
 	bazService := baz.New(bazConfig, barService)
 	mainService := &MainService{
 		Foo: service,
 		Bar: barService,
-		Baz: bazService,
+		baz: bazService,
 	}
 	return mainService
 }
@@ -31,25 +34,25 @@ func newMainService(config *foo.Config, barConfig *bar.Config, bazConfig *baz.Co
 type MainConfig struct {
 	Foo *foo.Config
 	Bar *bar.Config
-	Baz *baz.Config
+	baz *baz.Config
 }
 
 type MainService struct {
 	Foo *foo.Service
 	Bar *bar.Service
-	Baz *baz.Service
+	baz *baz.Service
 }
 
 func (m *MainService) String() string {
-	return fmt.Sprintf("%d %d %d", m.Foo.Cfg.V, m.Bar.Cfg.V, m.Baz.Cfg.V)
+	return fmt.Sprintf("%d %d %d", m.Foo.Cfg.V, m.Bar.Cfg.V, m.baz.Cfg.V)
 }
 
 func main() {
-	cfg := &MainConfig{
+	cfg := MainConfig{
 		Foo: &foo.Config{1},
 		Bar: &bar.Config{2},
-		Baz: &baz.Config{3},
+		baz: &baz.Config{3},
 	}
-	svc := newMainService(cfg.Foo, cfg.Bar, cfg.Baz)
+	svc := newMainService(cfg)
 	fmt.Println(svc.String())
 }

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

@@ -69,3 +69,9 @@ func provideOneOfTwo() OneOfTwo {
 func provideTwoOfTwo() TwoOfTwo {
 	return 1
 }
+
+type S struct {
+	Cfg Config
+}
+
+type Config int

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

@@ -29,6 +29,7 @@ func injectBar() Bar {
 		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
+		wire.FieldsOf(new(S), "Cfg"),          // S.Cfg not needed -> error
 	)
 	return 0
 }

internal/wire/testdata/UnusedProviders/want/wire_errs.txt

@@ -4,4 +4,6 @@ example.com/foo/wire.go:x:y: inject injectBar: unused provider "provideUnused"
 
 example.com/foo/wire.go:x:y: inject injectBar: unused value of type string
 
-example.com/foo/wire.go:x:y: inject injectBar: unused interface binding to type example.com/foo.Fooer
+example.com/foo/wire.go:x:y: inject injectBar: unused interface binding to type example.com/foo.Fooer
+
+example.com/foo/wire.go:x:y: inject injectBar: unused field "example.com/foo.S".Cfg

internal/wire/wire.go

@@ -623,6 +623,8 @@ func injectPass(name string, sig *types.Signature, calls []call, ig *injectorGen
 			ig.funcProviderCall(lname, c, injectSig)
 		case valueExpr:
 			ig.valueExpr(lname, c)
+		case selectorExpr:
+			ig.fieldExpr(lname, c)
 		default:
 			panic("unknown kind")
 		}
@@ -715,6 +717,15 @@ func (ig *injectorGen) valueExpr(lname string, c *call) {
 	ig.p("\t%s := %s\n", lname, ig.g.values[c.valueExpr])
 }
 
+func (ig *injectorGen) fieldExpr(lname string, c *call) {
+	a := c.args[0]
+	if a < len(ig.paramNames) {
+		ig.p("\t%s := %s.%s\n", lname, ig.paramNames[a], c.name)
+	} else {
+		ig.p("\t%s := %s.%s\n", lname, ig.localNames[a-len(ig.paramNames)], c.name)
+	}
+}
+
 // nameInInjector reports whether name collides with any other identifier
 // in the current injector.
 func (ig *injectorGen) nameInInjector(name string) bool {