internal/wire: move field name into ProviderInput (#104)

Avoids having parallel arrays for conceptually related data.

internal/wire/analyze.go

@@ -179,8 +179,12 @@ dfs:
 			}
 			index.Set(curr.t, given.Len()+len(calls))
 			kind := funcProviderCall
+			fieldNames := []string(nil)
 			if p.IsStruct {
 				kind = structProvider
+				for _, arg := range p.Args {
+					fieldNames = append(fieldNames, arg.FieldName)
+				}
 			}
 			calls = append(calls, call{
 				kind:       kind,
@@ -188,7 +192,7 @@ dfs:
 				name:       p.Name,
 				args:       args,
 				varargs:    p.Varargs,
-				fieldNames: p.Fields,
+				fieldNames: fieldNames,
 				ins:        ins,
 				out:        curr.t,
 				hasCleanup: p.HasCleanup,

internal/wire/parse.go

@@ -160,10 +160,6 @@ type Provider struct {
 	// Otherwise it's a function.
 	IsStruct bool
 
-	// Fields lists the field names to populate. This will map 1:1 with
-	// elements in Args.
-	Fields []string
-
 	// Out is the set of types this provider produces. It will always
 	// contain at least one type.
 	Out []types.Type
@@ -181,7 +177,8 @@ type Provider struct {
 type ProviderInput struct {
 	Type types.Type
 
-	// TODO(light): Move field name into this struct.
+	// If the provider is a struct, FieldName will be the field name to set.
+	FieldName string
 }
 
 // Value describes a value expression.
@@ -724,7 +721,6 @@ func processStructProvider(fset *token.FileSet, typeName *types.TypeName) (*Prov
 		Name:     typeName.Name(),
 		Pos:      pos,
 		Args:     make([]ProviderInput, st.NumFields()),
-		Fields:   make([]string, st.NumFields()),
 		IsStruct: true,
 		Out:      []types.Type{out, types.NewPointer(out)},
 	}
@@ -732,8 +728,8 @@ func processStructProvider(fset *token.FileSet, typeName *types.TypeName) (*Prov
 		f := st.Field(i)
 		provider.Args[i] = ProviderInput{
 			Type:      f.Type(),
+			FieldName: f.Name(),
 		}
-		provider.Fields[i] = f.Name()
 		for j := 0; j < i; j++ {
 			if types.Identical(provider.Args[i].Type, provider.Args[j].Type) {
 				return nil, []error{notePosition(fset.Position(pos), fmt.Errorf("provider struct has multiple fields of type %s", types.TypeString(provider.Args[j].Type, nil)))}