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pgraph: Add a named error for detected cycles

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This makes it useful to find when a topological sort failed.
This commit is contained in:
James Shubin
2023-02-25 23:16:35 -05:00
parent a41789a746
commit 8366cf0873
1 changed files with 6 additions and 2 deletions
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8
pgraph/pgraph.go
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@@ -19,6 +19,7 @@
package pgraph package pgraph
import ( import (
"errors"
"fmt" "fmt"
"sort" "sort"
"strings" "strings"
@@ -26,6 +27,9 @@ import (
"github.com/purpleidea/mgmt/util/errwrap" "github.com/purpleidea/mgmt/util/errwrap"
) )
// ErrNotAcyclic specifies that a particular graph was not found to be a dag.
var ErrNotAcyclic = errors.New("not a dag!")
// Graph is the graph structure in this library. The graph abstract data type // Graph is the graph structure in this library. The graph abstract data type
// (ADT) is defined as follows: // (ADT) is defined as follows:
// * The directed graph arrows point from left to right. ( -> ) // * The directed graph arrows point from left to right. ( -> )
@@ -599,7 +603,7 @@ func (g *Graph) TopologicalSort() ([]Vertex, error) { // kahn's algorithm
if in > 0 { if in > 0 {
for n := range g.adjacency[c] { for n := range g.adjacency[c] {
if remaining[n] > 0 { if remaining[n] > 0 {
return nil, fmt.Errorf("not a dag") return nil, ErrNotAcyclic
} }
} }
} }
@@ -622,7 +626,7 @@ func (g *Graph) Reachability(a, b Vertex) ([]Vertex, error) {
return nil, fmt.Errorf("empty vertex") return nil, fmt.Errorf("empty vertex")
} }
if _, err := g.TopologicalSort(); err != nil { if _, err := g.TopologicalSort(); err != nil {
return nil, err // not a dag? return nil, err // not a dag!
} }
vertices := g.OutgoingGraphVertices(a) // what points away from a ? vertices := g.OutgoingGraphVertices(a) // what points away from a ?