blob: 21657cd203210b93b710a473441ac2517ce35368 [file] [log] [blame]
// Copyright 2017 The Wuffs 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 ast
import (
t "github.com/google/wuffs/lang/token"
)
func TopologicalSortStructs(ns []*Struct) (sorted []*Struct, ok bool) {
// Algorithm is a depth-first search as per
// https://en.wikipedia.org/wiki/Topological_sorting#Depth-first_search
sorted = make([]*Struct, 0, len(ns))
byQID := map[t.QID]*Struct{}
for _, n := range ns {
byQID[n.QID()] = n
}
marks := map[*Struct]uint8{}
for _, n := range ns {
if _, ok := marks[n]; !ok {
sorted, ok = tssVisit(sorted, n, byQID, marks)
if !ok {
return nil, false
}
}
}
return sorted, true
}
func tssVisit(dst []*Struct, n *Struct, byQID map[t.QID]*Struct, marks map[*Struct]uint8) ([]*Struct, bool) {
const (
unmarked = 0
temporary = 1
permanent = 2
)
switch marks[n] {
case temporary:
return nil, false
case permanent:
return dst, true
}
marks[n] = temporary
for _, f := range n.Fields() {
x := f.AsField().XType().Innermost()
if o := byQID[x.QID()]; o != nil {
var ok bool
dst, ok = tssVisit(dst, o, byQID, marks)
if !ok {
return nil, false
}
}
}
marks[n] = permanent
return append(dst, n), true
}