Merge pull request moby#5180 from tonistiigi/stack-compress

stack: compress shared stacks for clearer output

Author: crazy-max

util/stack/compress.go

@@ -0,0 +1,67 @@
+package stack
+
+import (
+	"slices"
+)
+
+func compressStacks(st []*Stack) []*Stack {
+	if len(st) == 0 {
+		return nil
+	}
+
+	slices.SortFunc(st, func(a, b *Stack) int {
+		return len(b.Frames) - len(a.Frames)
+	})
+
+	out := []*Stack{st[0]}
+
+loop0:
+	for _, st := range st[1:] {
+		maxIdx := -1
+		for _, prev := range out {
+			idx := subFrames(st.Frames, prev.Frames)
+			if idx == -1 {
+				continue
+			}
+			// full match, potentially skip all
+			if idx == len(st.Frames)-1 {
+				if st.Pid == prev.Pid && st.Version == prev.Version && slices.Compare(st.Cmdline, st.Cmdline) == 0 {
+					continue loop0
+				}
+			}
+			if idx > maxIdx {
+				maxIdx = idx
+			}
+		}
+
+		if maxIdx > 0 {
+			st.Frames = st.Frames[:len(st.Frames)-maxIdx]
+		}
+		out = append(out, st)
+	}
+
+	return out
+}
+
+func subFrames(a, b []*Frame) int {
+	idx := -1
+	i := len(a) - 1
+	j := len(b) - 1
+	for i >= 0 {
+		if j < 0 {
+			break
+		}
+		if a[i].Equal(b[j]) {
+			idx++
+			i--
+			j--
+		} else {
+			break
+		}
+	}
+	return idx
+}
+
+func (a *Frame) Equal(b *Frame) bool {
+	return a.File == b.File && a.Line == b.Line && a.Name == b.Name
+}

util/stack/compress_test.go

@@ -0,0 +1,54 @@
+package stack
+
+import (
+	"testing"
+
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/require"
+)
+
+func testcall1() error {
+	return errors.Errorf("error1")
+}
+
+func testcall2() error {
+	return errors.WithStack(testcall1())
+}
+
+func testcall3() error {
+	err := testcall2()
+	// this is from a different line
+	return errors.WithStack(err)
+}
+
+func TestCompressStacks(t *testing.T) {
+	err := testcall2()
+	st := Traces(err)
+
+	// full trace match, shorter is removed
+	require.Len(t, st, 1)
+	require.GreaterOrEqual(t, len(st[0].Frames), 2)
+
+	f := st[0].Frames
+	require.Contains(t, f[0].Name, "testcall1")
+	require.Contains(t, f[1].Name, "testcall2")
+}
+
+func TestCompressMultiStacks(t *testing.T) {
+	err := testcall3()
+	st := Traces(err)
+
+	require.Len(t, st, 2)
+	require.GreaterOrEqual(t, len(st[0].Frames), 4)
+
+	f1 := st[0].Frames
+	require.Contains(t, f1[0].Name, "testcall1")
+	require.Contains(t, f1[1].Name, "testcall2")
+	require.Contains(t, f1[2].Name, "testcall3")
+
+	f2 := st[1].Frames
+	require.Contains(t, f2[0].Name, "testcall3")
+	// next line is shared and everything after is removed
+	require.Len(t, f2, 2)
+	require.Equal(t, f1[3], f2[1])
+}

util/stack/stack.go

@@ -44,6 +44,10 @@ func Helper() {
 }
 
 func Traces(err error) []*Stack {
+	return compressStacks(traces(err))
+}
+
+func traces(err error) []*Stack {
 	var st []*Stack
 
 	switch e := err.(type) {