Adding capability to auto-bind a type to interfaces it implements

internal/wire/analyze.go

@@ -287,6 +287,18 @@ func verifyArgsUsed(set *ProviderSet, used []*providerSetSrc) []error {
 			errs = append(errs, fmt.Errorf("unused provider %q", p.Pkg.Name()+"."+p.Name))
 		}
 	}
+	for _, ab := range set.AutoBindings {
+		found := false
+		for _, u := range used {
+			if u.AutoBinding == ab {
+				found = true
+				break
+			}
+		}
+		if !found {
+			errs = append(errs, fmt.Errorf("unused auto binding %q", types.TypeString(ab.Concrete, nil)))
+		}
+	}
 	for _, v := range set.Values {
 		found := false
 		for _, u := range used {
@@ -458,49 +470,50 @@ func verifyAcyclic(providerMap *typeutil.Map, hasher typeutil.Hasher) []error {
 				continue
 			}
 			pt := x.(*ProvidedType)
+			var args []types.Type
 			switch {
 			case pt.IsValue():
 				// Leaf: values do not have dependencies.
 			case pt.IsArg():
 				// Injector arguments do not have dependencies.
-			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)
+			case pt.IsProvider():
+				for _, arg := range pt.Provider().Args {
+					args = append(args, arg.Type)
 				}
-				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)
-								}
+			case pt.IsAutoBinding():
+				args = append(args, pt.AutoBinding().Concrete)
+			case pt.IsField():
+				args = append(args, pt.Field().Parent)
+			default:
+				panic("invalid provider map value")
+			}
+
+			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
 						}
-					}
-					if !hasCycle {
-						next := append(append([]types.Type(nil), curr...), a)
-						stk = append(stk, next)
+						fmt.Fprintf(sb, "%s", types.TypeString(a, nil))
+						ec.add(errors.New(sb.String()))
+						hasCycle = true
+						break
 					}
 				}
-			default:
-				panic("invalid provider map value")
+				if !hasCycle {
+					next := append(append([]types.Type(nil), curr...), a)
+					stk = append(stk, next)
+				}
 			}
 		}
 	}

internal/wire/parse.go

@@ -35,6 +35,7 @@ import (
 // Exactly one of the fields will be set.
 type providerSetSrc struct {
 	Provider    *Provider
+	AutoBinding *AutoBinding
 	Binding     *IfaceBinding
 	Value       *Value
 	Import      *ProviderSet
@@ -57,6 +58,8 @@ func (p *providerSetSrc) description(fset *token.FileSet, typ types.Type) string
 			kind = "struct provider"
 		}
 		return fmt.Sprintf("%s %s(%s)", kind, quoted(p.Provider.Name), fset.Position(p.Provider.Pos))
+	case p.AutoBinding != nil:
+		return fmt.Sprintf("wire.AutoBind (%s)", fset.Position(p.AutoBinding.Pos))
 	case p.Binding != nil:
 		return fmt.Sprintf("wire.Bind (%s)", fset.Position(p.Binding.Pos))
 	case p.Value != nil:
@@ -98,11 +101,12 @@ type ProviderSet struct {
 	// variable.
 	VarName string
 
-	Providers []*Provider
-	Bindings  []*IfaceBinding
-	Values    []*Value
-	Fields    []*Field
-	Imports   []*ProviderSet
+	Providers    []*Provider
+	Bindings     []*IfaceBinding
+	AutoBindings []*AutoBinding
+	Values       []*Value
+	Fields       []*Field
+	Imports      []*ProviderSet
 	// InjectorArgs is only filled in for wire.Build.
 	InjectorArgs *InjectorArgs
 
@@ -125,6 +129,22 @@ func (set *ProviderSet) Outputs() []types.Type {
 func (set *ProviderSet) For(t types.Type) ProvidedType {
 	pt := set.providerMap.At(t)
 	if pt == nil {
+		// if t is an interface, we may have an AutoBinding that implements it.
+		iface, ok := t.Underlying().(*types.Interface)
+		if !ok {
+			return ProvidedType{}
+		}
+
+		for _, ab := range set.AutoBindings {
+			if types.Implements(ab.Concrete, iface) {
+				// cache for later
+				pt := &ProvidedType{t: ab.Concrete, ab: ab}
+				set.providerMap.Set(t, pt)
+				set.srcMap.Set(t, &providerSetSrc{AutoBinding: ab})
+				return *pt
+			}
+		}
+
 		return ProvidedType{}
 	}
 	return *pt.(*ProvidedType)
@@ -179,6 +199,17 @@ type Provider struct {
 	HasErr bool
 }
 
+// AutoBinding records the signature of a provider eligible for auto-binding
+// to interfaces it implements. A provider is a single Go object, either a
+// function or a named type.
+type AutoBinding struct {
+	// Concrete is always a type that implements N number of interfaces.
+	Concrete types.Type
+
+	// Pos is the position where the binding was declared.
+	Pos token.Pos
+}
+
 // ProviderInput describes an incoming edge in the provider graph.
 type ProviderInput struct {
 	Type types.Type
@@ -520,7 +551,7 @@ func (oc *objectCache) varDecl(obj *types.Var) *ast.ValueSpec {
 }
 
 // processExpr converts an expression into a Wire structure. It may return a
-// *Provider, an *IfaceBinding, a *ProviderSet, a *Value or a []*Field.
+// *Provider, an *AutoBinding, 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)
@@ -546,6 +577,12 @@ func (oc *objectCache) processExpr(info *types.Info, pkgPath string, expr ast.Ex
 		case "NewSet":
 			pset, errs := oc.processNewSet(info, pkgPath, call, nil, varName)
 			return pset, notePositionAll(exprPos, errs)
+		case "AutoBind":
+			abs, err := processAutoBind(oc.fset, info, call)
+			if err != nil {
+				return nil, []error{notePosition(exprPos, err)}
+			}
+			return abs, nil
 		case "Bind":
 			b, err := processBind(oc.fset, info, call)
 			if err != nil {
@@ -607,6 +644,8 @@ func (oc *objectCache) processNewSet(info *types.Info, pkgPath string, call *ast
 			continue
 		}
 		switch item := item.(type) {
+		case *AutoBinding:
+			pset.AutoBindings = append(pset.AutoBindings, item)
 		case *Provider:
 			pset.Providers = append(pset.Providers, item)
 		case *ProviderSet:
@@ -880,6 +919,41 @@ func isPrevented(tag string) bool {
 	return reflect.StructTag(tag).Get("wire") == "-"
 }
 
+func processAutoBind(fset *token.FileSet, info *types.Info, call *ast.CallExpr) (*AutoBinding, error) {
+	// Assumes that call.Fun is wire.AutoBind.
+
+	if len(call.Args) != 1 {
+		return nil, notePosition(fset.Position(call.Pos()),
+			errors.New("call to AutoBind takes exactly one argument"))
+	}
+	const firstArgReqFormat = "first argument to AutoBind must be a pointer to a type; found %s"
+	typ := info.TypeOf(call.Args[0])
+	ptr, ok := typ.(*types.Pointer)
+	if !ok {
+		return nil, notePosition(fset.Position(call.Pos()),
+			fmt.Errorf(firstArgReqFormat, types.TypeString(typ, nil)))
+	}
+
+	switch ptr.Elem().Underlying().(type) {
+	case *types.Named,
+		*types.Struct,
+		*types.Basic:
+		// good!
+
+	default:
+		return nil, notePosition(fset.Position(call.Pos()),
+			fmt.Errorf(firstArgReqFormat, types.TypeString(ptr, nil)))
+	}
+
+	typeExpr := call.Args[0].(*ast.CallExpr)
+	typeName := qualifiedIdentObject(info, typeExpr.Args[0]) // should be either an identifier or selector
+	autoBinding := &AutoBinding{
+		Concrete: ptr,
+		Pos:      typeName.Pos(),
+	}
+	return autoBinding, nil
+}
+
 // processBind creates an interface binding from a wire.Bind call.
 func processBind(fset *token.FileSet, info *types.Info, call *ast.CallExpr) (*IfaceBinding, error) {
 	// Assumes that call.Fun is wire.Bind.
@@ -1122,7 +1196,6 @@ func findInjectorBuild(info *types.Info, fn *ast.FuncDecl) (*ast.CallExpr, error
 		default:
 			invalid = true
 		}
-
 	}
 	if wireBuildCall == nil {
 		return nil, nil
@@ -1157,16 +1230,17 @@ func isProviderSetType(t types.Type) bool {
 // none of the above, and returns true for IsNil.
 type ProvidedType struct {
 	// t is the provided concrete type.
-	t types.Type
-	p *Provider
-	v *Value
-	a *InjectorArg
-	f *Field
+	t  types.Type
+	p  *Provider
+	ab *AutoBinding
+	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 && pt.f == nil
+	return pt.p == nil && pt.ab == nil && pt.v == nil && pt.a == nil && pt.f == nil
 }
 
 // Type returns the output type.
@@ -1185,6 +1259,11 @@ func (pt ProvidedType) IsProvider() bool {
 	return pt.p != nil
 }
 
+// IsAutoBinding reports whether pt points to an AutoBinding.
+func (pt ProvidedType) IsAutoBinding() bool {
+	return pt.ab != nil
+}
+
 // IsValue reports whether pt points to a Value.
 func (pt ProvidedType) IsValue() bool {
 	return pt.v != nil
@@ -1209,6 +1288,15 @@ func (pt ProvidedType) Provider() *Provider {
 	return pt.p
 }
 
+// AutoBinding returns pt as a AutoBinding pointer. It panics if pt does not point
+// to a AutoBinding.
+func (pt ProvidedType) AutoBinding() *AutoBinding {
+	if pt.ab == nil {
+		panic("ProvidedType does not hold an AutoBinding")
+	}
+	return pt.ab
+}
+
 // Value returns pt as a Value pointer. It panics if pt does not point
 // to a Value.
 func (pt ProvidedType) Value() *Value {

internal/wire/testdata/InterfaceAutoBinding/foo/foo.go

@@ -0,0 +1,43 @@
+// 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"
+
+	"github.com/google/wire"
+)
+
+func main() {
+	fmt.Println(injectFooer().Foo())
+}
+
+type Fooer interface {
+	Foo() string
+}
+
+type Bar string
+
+func (b *Bar) Foo() string {
+	return string(*b)
+}
+
+func provideBar() *Bar {
+	b := new(Bar)
+	*b = "Hello, World!"
+	return b
+}
+
+var Set = wire.NewSet(provideBar)

internal/wire/testdata/InterfaceAutoBinding/foo/wire.go

@@ -0,0 +1,26 @@
+// 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 injectFooer() Fooer {
+	wire.Build(Set, wire.AutoBind(new(Bar)))
+	return nil
+}

internal/wire/testdata/InterfaceAutoBinding/pkg

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

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

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