fix(itg): restore failed incremental hashes for BUG-029

core/itg/graph/update.go

@@ -186,6 +186,23 @@ func computeAvailableHashes(
 
 // computeHashes computes hashes recursively for the given target ID.
 func (g *OptimizedGraph) computeHashes(ctx context.Context, id int) ([]byte, error) {
+	computed := make(map[int][]byte)
+	hash, err := g.computeHashesRecursively(ctx, id, NewIntSet(), computed)
+	if err != nil {
+		return nil, err
+	}
+	for targetID, targetHash := range computed {
+		g.OptimizedTargets[targetID].Hash = targetHash
+	}
+	return hash, nil
+}
+
+func (g *OptimizedGraph) computeHashesRecursively(
+	ctx context.Context,
+	id int,
+	visiting IntSet,
+	computed map[int][]byte,
+) ([]byte, error) {
 	if ctx.Err() != nil {
 		return nil, context.Cause(ctx)
 	}
@@ -201,9 +218,16 @@ func (g *OptimizedGraph) computeHashes(ctx context.Context, id int) ([]byte, err
 	if target.Hash != nil {
 		return target.Hash, nil
 	}
+	if hash, ok := computed[id]; ok {
+		return hash, nil
+	}
+	if visiting.Contains(id) {
+		return []byte{}, nil
+	}
+
+	visiting.Insert(id)
+	defer visiting.Delete(id)
 
-	// mark as visiting to handle cycles
-	target.Hash = []byte{}
 	var hash []byte
 	switch g.RuleTypeIDToString[target.RuleType] {
 	case targethasher.SourceFileType, targethasher.PackageGroup:
@@ -214,7 +238,7 @@ func (g *OptimizedGraph) computeHashes(ctx context.Context, id int) ([]byte, err
 			singleDep = dep
 			break
 		}
-		dephash, err := g.computeHashes(ctx, singleDep)
+		dephash, err := g.computeHashesRecursively(ctx, singleDep, visiting, computed)
 		if err != nil {
 			return nil, err
 		}
@@ -230,7 +254,7 @@ func (g *OptimizedGraph) computeHashes(ctx context.Context, id int) ([]byte, err
 			return strings.Compare(g.TargetIDToString[i], g.TargetIDToString[j])
 		})
 		for _, dep := range depIDs {
-			dephash, err := g.computeHashes(ctx, dep)
+			dephash, err := g.computeHashesRecursively(ctx, dep, visiting, computed)
 			if err != nil {
 				return nil, err
 			}
@@ -239,7 +263,7 @@ func (g *OptimizedGraph) computeHashes(ctx context.Context, id int) ([]byte, err
 		hash = h.Sum(nil)
 	}
 	if hash != nil {
-		target.Hash = hash
+		computed[id] = hash
 	}
 	return hash, nil
 }

core/itg/graph/update_test.go

@@ -15,8 +15,10 @@
 package graph
 
 import (
+	"bytes"
 	"context"
 	"crypto/sha1"
+	"encoding/gob"
 	"testing"
 
 	buildpb "github.com/bazelbuild/buildtools/build_proto"
@@ -231,4 +233,66 @@ func TestComputeHashes(t *testing.T) {
 		h.Write(depHash)
 		assert.Equal(t, h.Sum(nil), got)
 	})
+
+	t.Run("failed traversal restores hashes before retry", func(t *testing.T) {
+		t.Parallel()
+		goodName := "//pkg:a_good"
+		badName := "//pkg:z_bad.go"
+		rootName := "//pkg:root"
+		goodHashWithoutDeps := []byte{0x01, 0x02}
+		rootHashWithoutDeps := []byte{0x03, 0x04}
+		g := OptimizeGraph(map[string]*targethasher.Target{
+			goodName: {
+				Name:            goodName,
+				RuleType:        "go_library",
+				HashWithoutDeps: goodHashWithoutDeps,
+			},
+			badName: {
+				Name:     badName,
+				RuleType: targethasher.SourceFileType,
+			},
+			rootName: {
+				Name:            rootName,
+				RuleType:        "go_library",
+				HashWithoutDeps: rootHashWithoutDeps,
+				Deps:            []string{badName, goodName},
+			},
+		})
+		goodID := g.TargetNameToID[goodName]
+		badID := g.TargetNameToID[badName]
+		rootID := g.TargetNameToID[rootName]
+
+		_, err := g.computeHashes(context.Background(), rootID)
+		require.Error(t, err)
+		assert.Nil(t, g.OptimizedTargets[rootID].Hash)
+		assert.Nil(t, g.OptimizedTargets[goodID].Hash)
+		assert.Nil(t, g.OptimizedTargets[badID].Hash)
+
+		var persisted bytes.Buffer
+		require.NoError(t, gob.NewEncoder(&persisted).Encode(g))
+		var restored OptimizedGraph
+		require.NoError(t, gob.NewDecoder(&persisted).Decode(&restored))
+		assert.Nil(t, restored.OptimizedTargets[rootID].Hash)
+		assert.Nil(t, restored.OptimizedTargets[goodID].Hash)
+
+		badHash := []byte{0x05, 0x06}
+		g.OptimizedTargets[badID].Hash = badHash
+
+		got, err := g.computeHashes(context.Background(), rootID)
+		require.NoError(t, err)
+
+		goodHasher := sha1.New()
+		goodHasher.Write(goodHashWithoutDeps)
+		goodHash := goodHasher.Sum(nil)
+		rootHasher := sha1.New()
+		rootHasher.Write(rootHashWithoutDeps)
+		rootHasher.Write(goodHash)
+		rootHasher.Write(badHash)
+		expected := rootHasher.Sum(nil)
+
+		assert.Equal(t, goodHash, g.OptimizedTargets[goodID].Hash)
+		assert.Equal(t, expected, got)
+		assert.Equal(t, expected, g.OptimizedTargets[rootID].Hash)
+		assert.NotEmpty(t, got)
+	})
 }