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fix: detect cyclic dependency in the graph #1046

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Skarlso wants to merge 2 commits into from
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fix: detect cyclic dependency in the graph #1046

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0b91ebd
fix: detect cyclic dependency in the graph
Skarlso Oct 15, 2025
630559b
fix the cyclic detection
Skarlso Oct 15, 2025
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21 changes: 19 additions & 2 deletions bindings/go/dag/sync/discover.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ import (
"context"
"errors"
"fmt"
"maps"
"sync"

"golang.org/x/sync/errgroup"
Expand Down Expand Up @@ -155,7 +156,9 @@ func (d *GraphDiscoverer[K, V]) Discover(ctx context.Context) (retErr error) {
errGroup, errgroupCtx := errgroup.WithContext(ctx)
for _, root := range d.opts.Roots {
errGroup.Go(func() error {
return d.discover(errgroupCtx, root)
// create empty path for each root
path := make(map[K]bool)
return d.discover(errgroupCtx, root, path)
})
}

Expand All @@ -169,6 +172,7 @@ func (d *GraphDiscoverer[K, V]) Discover(ctx context.Context) (retErr error) {
func (d *GraphDiscoverer[K, V]) discover(
ctx context.Context,
id K,
path map[K]bool,
) error {
// Early abort if context is cancelled.
select {
Expand All @@ -177,6 +181,11 @@ func (d *GraphDiscoverer[K, V]) discover(
default:
}

// if we have a match, error out
if path[id] {
return fmt.Errorf("cyclic dependency detected: vertex %v is already in the current discovery path", id)
}

// Setup done channel for this vertex.
ch := make(chan struct{})
defer close(ch)
Expand All @@ -193,6 +202,11 @@ func (d *GraphDiscoverer[K, V]) discover(
}
}

// add this vertex to the current discovery path
path[id] = true
// remove this vertex from the path when done (part of the backtracking)
defer delete(path, id)

// Add vertex in "discovering" state.
if err := d.graph.WithWriteLock(func(d *dag.DirectedAcyclicGraph[K]) error {
return d.AddVertex(id, map[string]any{
Expand Down Expand Up @@ -237,7 +251,10 @@ func (d *GraphDiscoverer[K, V]) discover(
errGroup, egctx := errgroup.WithContext(ctx)
for index, neighbor := range neighbors {
errGroup.Go(func() error {
if err := d.discover(egctx, neighbor); err != nil {
// create a copy for this particular neighbor
childPath := maps.Clone(path)

if err := d.discover(egctx, neighbor, childPath); err != nil {
return fmt.Errorf("failed to discover reference %v: %w", neighbor, err)
}
// Add edge from current vertex to neighbor.
Expand Down
45 changes: 45 additions & 0 deletions bindings/go/dag/sync/discover_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -129,6 +129,51 @@ func TestDAGDiscovery(t *testing.T) {
r.Contains([]DiscoveryState{DiscoveryStateError, DiscoveryStateUnknown}, cState, "expected vertex C to be in error state, but got %s", cState)
})

t.Run("graph discovery fails in case of cyclic dependency", func(t *testing.T) {
ctx := t.Context()
r := require.New(t)
// Emulate an invalid external dependency graph. Here, the edge C -> D
// exists, but D is not found in the graph.
// A
// / \
// B - B
Comment on lines +135 to +139

@ikhandamirov ikhandamirov Oct 15, 2025

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This comment does not seem to describe a cyclic dependency.

graph := map[string][]string{
"A": {"B"},
"B": {"A"},
}
dag := NewGraphDiscoverer(&GraphDiscovererOptions[string, string]{
Roots: []string{"A"},
Resolver: ResolverFunc[string, string](func(ctx context.Context, key string) (value string, err error) {
if _, ok := graph[key]; !ok {
return "", fmt.Errorf("no node found with ID %s", key)
}
return key, nil
}),
Discoverer: DiscovererFunc[string, string](func(ctx context.Context, parent string) (children []string, err error) {
dep, ok := graph[parent]
if !ok {
return nil, fmt.Errorf("no node found with ID %s", parent)
}
var neighbors []string
for _, id := range dep {
neighbors = append(neighbors, id)
}
return neighbors, nil
}),
})

err := dag.Discover(ctx)
r.Error(err, "expected error due to missing node in the external graph, but got nil")

aState := dag.CurrentState("A")
r.Equal(DiscoveryStateError, aState, "expected vertex A to be in error state, but got %s", aState)

// because of discovers property to abort early, if 2 nodes on the layer are running in parallel,
// and one of them fails, the other one might be in an unknown state as it might not have yet been discovered.
bState := dag.CurrentState("B")
r.Contains([]DiscoveryState{DiscoveryStateError, DiscoveryStateUnknown}, bState, "expected vertex B to be in error state, but got %s", bState)
})

t.Run("graph discovery fails in discovery function", func(t *testing.T) {
ctx := t.Context()
r := require.New(t)
Expand Down
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