cycle.go

Documentation: cuelang.org/go/tools/flow

     1  // Copyright 2020 CUE Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package flow
    16  
    17  import (
    18  	"fmt"
    19  	"strings"
    20  
    21  	"cuelang.org/go/cue"
    22  	"cuelang.org/go/cue/errors"
    23  	"cuelang.org/go/cue/token"
    24  )
    25  
    26  // checkCycle checks for cyclic dependencies between tasks.
    27  func checkCycle(a []*Task) errors.Error {
    28  	cc := cycleChecker{
    29  		visited: make([]bool, len(a)),
    30  		stack:   make([]*Task, 0, len(a)),
    31  	}
    32  	for _, t := range a {
    33  		if cc.isCyclic(t) {
    34  			break
    35  		}
    36  	}
    37  	return cc.err
    38  }
    39  
    40  type cycleChecker struct {
    41  	visited []bool
    42  	stack   []*Task
    43  	err     errors.Error
    44  }
    45  
    46  func (cc *cycleChecker) isCyclic(t *Task) bool {
    47  	i := t.index
    48  	if !cc.visited[i] {
    49  		cc.visited[i] = true
    50  		cc.stack = append(cc.stack, t)
    51  
    52  		for _, d := range t.depTasks {
    53  			if !cc.visited[d.index] && cc.isCyclic(d) {
    54  				return true
    55  			} else if cc.visited[d.index] {
    56  				cc.addCycleError(t)
    57  				return true
    58  			}
    59  		}
    60  	}
    61  	cc.stack = cc.stack[:len(cc.stack)-1]
    62  	cc.visited[i] = false
    63  	return false
    64  }
    65  
    66  func (cc *cycleChecker) addCycleError(start *Task) {
    67  	err := &cycleError{}
    68  
    69  	for _, t := range cc.stack {
    70  		err.path = append(err.path, t.v.Path())
    71  		err.positions = append(err.positions, t.v.Pos())
    72  	}
    73  
    74  	cc.err = errors.Append(cc.err, err)
    75  }
    76  
    77  type cycleError struct {
    78  	path      []cue.Path
    79  	positions []token.Pos
    80  }
    81  
    82  func (e *cycleError) Error() string {
    83  	msg, args := e.Msg()
    84  	return fmt.Sprintf(msg, args...)
    85  }
    86  
    87  func (e *cycleError) Path() []string { return nil }
    88  
    89  func (e *cycleError) Msg() (format string, args []interface{}) {
    90  	w := &strings.Builder{}
    91  	for _, p := range e.path {
    92  		fmt.Fprintf(w, "\n\ttask %s refers to", p)
    93  	}
    94  	fmt.Fprintf(w, "\n\ttask %s", e.path[0])
    95  
    96  	return "cyclic task dependency:%v", []interface{}{w.String()}
    97  }
    98  
    99  func (e *cycleError) Position() token.Pos {
   100  	if len(e.positions) == 0 {
   101  		return token.NoPos
   102  	}
   103  	return e.positions[0]
   104  }
   105  
   106  func (e *cycleError) InputPositions() []token.Pos {
   107  	return e.positions
   108  }
   109
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