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")
 			}
 		}
 	}