internal/pkg: in-flight error resolution

The DCE is a slow and overcomplicated solution to a simple problem. This change replaces the DCE by resolving errors in-flight.

Signed-off-by: Ophestra <cat@gensokyo.uk>

4 files changed, 81 insertions, 163 deletions

diff --git a/cmd/mbf/main.go b/cmd/mbf/main.go
index 2312c818..0024275a 100644
--- a/cmd/mbf/main.go
+++ b/cmd/mbf/main.go
@@ -1196,6 +1196,10 @@ func main() {
 		if w, ok := err.(interface{ Unwrap() []error }); !ok {
 			log.Fatal(err)
 		} else {
+			if _, ok = w.(pkg.InputError); ok {
+				log.Fatal(w)
+			}
+
 			errs := w.Unwrap()
 			for i, e := range errs {
 				if i == len(errs)-1 {
diff --git a/internal/pkg/exec_test.go b/internal/pkg/exec_test.go
index 28ca2002..222ab790 100644
--- a/internal/pkg/exec_test.go
+++ b/internal/pkg/exec_test.go
@@ -118,11 +118,8 @@ func TestExec(t *testing.T) {
 					[]string{"testtool"},
 
 					pkg.MustPath("/proc/nonexistent", false, failingArtifact),
-				), nil, nil, pkg.WNew, &pkg.DependencyCureError{
-					{
-						A:   failingArtifact,
-						Err: stub.UniqueError(0xcafe),
-					},
+				), nil, nil, pkg.WNew, pkg.InputError{
+					failingArtifact: stub.UniqueError(0xcafe),
 				}},
 
 				{"invalid paths", pkg.NewExec(
diff --git a/internal/pkg/pkg.go b/internal/pkg/pkg.go
index 8dd6abcc..220f268d 100644
--- a/internal/pkg/pkg.go
+++ b/internal/pkg/pkg.go
@@ -18,7 +18,6 @@ import (
 	"maps"
 	"math"
 	"os"
-	"os/signal"
 	"path/filepath"
 	"runtime"
 	"slices"
@@ -654,10 +653,10 @@ type pendingArtifactDep struct {
 	// if curing succeeds.
 	resP *cureRes
 
-	// Address of result error slice populated during [Cache.Cure], dereferenced
+	// Address of result error map populated during [Cache.Cure], dereferenced
 	// after acquiring errsMu if curing fails. No additional action is taken,
 	// [Cache] and its caller are responsible for further error handling.
-	errs *DependencyCureError
+	errs InputError
 	// Address of mutex synchronising access to errs.
 	errsMu *sync.Mutex
 
@@ -1721,109 +1720,43 @@ retry:
 	goto retry
 }
 
-// CureError wraps a non-nil error returned attempting to cure an [Artifact].
-type CureError struct {
-	A   Artifact
-	Err error
-}
-
-// Unwrap returns the underlying error.
-func (e *CureError) Unwrap() error { return e.Err }
-
-// Error returns the error message from the underlying Err.
-func (e *CureError) Error() string { return e.Err.Error() }
-
-// A DependencyCureError wraps errors returned while curing dependencies.
-type DependencyCureError []*CureError
-
-// unwrapM recursively expands underlying errors into a caller-supplied map.
-func (e *DependencyCureError) unwrapM(
-	ctx context.Context,
-	ir *IRCache,
-	me map[unique.Handle[ID]]*CureError,
-) {
-	for _, err := range *e {
-		if ctx.Err() != nil {
-			break
-		}
+// An InputError describes inputs of a [FloodArtifact] which had failed to cure.
+type InputError map[Artifact]error
 
-		id := ir.Ident(err.A)
-		if _, ok := me[id]; ok {
-			continue
-		}
-		if _e, ok := err.Err.(*DependencyCureError); ok {
-			_e.unwrapM(ctx, ir, me)
-			continue
-		}
-		me[id] = err
-	}
-}
+// Error returns a user-facing, deterministic text representation of e.
+func (e InputError) Error() string {
+	ir := NewIR()
 
-// unwrap recursively expands and deduplicates underlying errors.
-func (e *DependencyCureError) unwrap(
-	ctx context.Context,
-	ir *IRCache,
-) DependencyCureError {
-	me := make(map[unique.Handle[ID]]*CureError)
-	e.unwrapM(ctx, ir, me)
-	type ent struct {
-		id  unique.Handle[ID]
-		err *CureError
+	type input struct {
+		a  Artifact
+		id unique.Handle[ID]
 	}
-	errs := make([]*ent, 0, len(me))
-	for id, err := range me {
-		errs = append(errs, &ent{id, err})
+	p := make([]input, 0, len(e))
+	for a := range e {
+		p = append(p, input{a, ir.Ident(a)})
 	}
 
 	var identBuf [2]ID
-	slices.SortFunc(errs, func(a, b *ent) int {
+	slices.SortFunc(p, func(a, b input) int {
 		identBuf[0], identBuf[1] = a.id.Value(), b.id.Value()
 		return slices.Compare(identBuf[0][:], identBuf[1][:])
 	})
 
-	_errs := make(DependencyCureError, len(errs))
-	for i, v := range errs {
-		_errs[i] = v.err
-	}
-	return _errs
-}
-
-// Unwrap returns a deduplicated slice of underlying errors.
-func (e *DependencyCureError) Unwrap() []error {
-	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
-	defer cancel()
-
-	errs := e.unwrap(ctx, NewIR())
-	_errs := make([]error, len(errs))
-	for i, err := range errs {
-		_errs[i] = err
-	}
-	return _errs
-}
-
-// Error returns a user-facing multiline error message.
-func (e *DependencyCureError) Error() string {
-	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
-	defer cancel()
-
-	ir := NewIR()
-	errs := e.unwrap(ctx, ir)
-	if len(errs) == 0 {
-		return "invalid dependency cure outcome"
-	}
 	var buf strings.Builder
-	buf.WriteString("errors curing dependencies:")
-	for _, err := range errs {
+	buf.WriteString("errors curing inputs:")
+	for _, i := range p {
 		buf.WriteString("\n\t" +
-			reportName(err.A, ir.Ident(err.A)) + ": " +
-			err.Error())
-	}
-	if ctx.Err() != nil {
-		buf.WriteString("\nerror resolution cancelled")
+			reportName(i.a, i.id) + ": " +
+			e[i.a].Error())
 	}
 	return buf.String()
 }
 
+// Unwrap returns a slice of underlying errors in unspecified order.
+func (e InputError) Unwrap() []error {
+	return slices.AppendSeq(make([]error, 0, len(e)), maps.Values(e))
+}
+
 // enterCure must be called before entering an [Artifact] implementation.
 func (c *Cache) enterCure(a Artifact, curesExempt bool) error {
 	if c.attr.Notify != nil {
@@ -2023,7 +1956,7 @@ func (c *Cache) cureMany(
 	wg.Add(len(inputs))
 	var mask []bool
 	res := make([]cureRes, len(inputs))
-	errs := make(DependencyCureError, 0, len(inputs))
+	errs := make(InputError)
 	var errsMu sync.Mutex
 	if shallow {
 		mask = make([]bool, len(inputs))
@@ -2042,13 +1975,13 @@ func (c *Cache) cureMany(
 				continue
 			}
 		}
-		pending := pendingArtifactDep{d, &res[i], &errs, &errsMu, &wg}
+		pending := pendingArtifactDep{d, &res[i], errs, &errsMu, &wg}
 		go pending.cure(c)
 	}
 	wg.Wait()
 
 	if len(errs) > 0 {
-		return mask, &errs
+		return mask, errs
 	}
 	for i, p := range res {
 		if shallow && mask[i] {
@@ -2651,7 +2584,11 @@ func (pending *pendingArtifactDep) cure(c *Cache) {
 	}
 
 	pending.errsMu.Lock()
-	*pending.errs = append(*pending.errs, &CureError{pending.a, err})
+	if errs, ok := err.(InputError); ok {
+		maps.Copy(pending.errs, errs)
+	} else {
+		pending.errs[pending.a] = err
+	}
 	pending.errsMu.Unlock()
 }
 
diff --git a/internal/pkg/pkg_test.go b/internal/pkg/pkg_test.go
index 1313d42c..a6964798 100644
--- a/internal/pkg/pkg_test.go
+++ b/internal/pkg/pkg_test.go
@@ -11,6 +11,7 @@ import (
 	"io"
 	"io/fs"
 	"log"
+	"maps"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -861,14 +862,11 @@ func TestCache(t *testing.T) {
 					cure: func(f *pkg.FContext) error {
 						panic("attempting to cure impossible artifact")
 					},
-				}, nil, nil, pkg.WNew, &pkg.DependencyCureError{
-					{
-						A: failingFile,
-						Err: struct {
-							_ []byte
-							stub.UniqueError
-						}{UniqueError: 0xbad},
-					},
+				}, nil, nil, pkg.WNew, pkg.InputError{
+					failingFile: struct {
+						_ []byte
+						stub.UniqueError
+					}{UniqueError: 0xbad},
 				}},
 			})
 
@@ -1949,7 +1947,7 @@ errors during scrub:
 	}
 }
 
-func TestDependencyCureError(t *testing.T) {
+func TestInputError(t *testing.T) {
 	t.Parallel()
 
 	makeIdent := func(ident ...byte) pkg.Artifact {
@@ -1962,56 +1960,24 @@ func TestDependencyCureError(t *testing.T) {
 
 	testCases := []struct {
 		name   string
-		err    pkg.DependencyCureError
+		err    pkg.InputError
 		want   string
 		unwrap []error
 	}{
-		{"simple", pkg.DependencyCureError{
-			{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
-			{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-			{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
-			{A: makeIdent(0xff, 1), Err: stub.UniqueError(0xbad01)},
-		}, `errors curing dependencies:
-	_wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765184 injected by the test suite
-	_wEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765185 injected by the test suite
-	_wkAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765193 injected by the test suite
-	_w8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765199 injected by the test suite`, []error{
-			&pkg.CureError{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-			&pkg.CureError{A: makeIdent(0xff, 1), Err: stub.UniqueError(0xbad01)},
-			&pkg.CureError{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
-			&pkg.CureError{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
-		}},
-
-		{"dedup", pkg.DependencyCureError{
-			{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
-			{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-			{A: makeIdent(0xff, 0xfd), Err: &pkg.DependencyCureError{
-				{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
-				{A: makeIdent(0xff, 0xc), Err: &pkg.DependencyCureError{
-					{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
-					{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-				}},
-				{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-				{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-			}},
-			{A: makeIdent(0xff, 0xff), Err: &pkg.DependencyCureError{
-				{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
-				{A: makeIdent(0xff, 0xc), Err: &pkg.DependencyCureError{
-					{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-				}},
-				{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-			}},
-			{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
-			{A: makeIdent(0xff, 1), Err: stub.UniqueError(0xbad01)},
-		}, `errors curing dependencies:
+		{"simple", pkg.InputError{
+			makeIdent(0xff, 9):   stub.UniqueError(0xbad09),
+			makeIdent(0xff, 0):   stub.UniqueError(0xbad00),
+			makeIdent(0xff, 0xf): stub.UniqueError(0xbad0f),
+			makeIdent(0xff, 1):   stub.UniqueError(0xbad01),
+		}, `errors curing inputs:
 	_wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765184 injected by the test suite
 	_wEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765185 injected by the test suite
 	_wkAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765193 injected by the test suite
 	_w8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA: unique error 765199 injected by the test suite`, []error{
-			&pkg.CureError{A: makeIdent(0xff, 0), Err: stub.UniqueError(0xbad00)},
-			&pkg.CureError{A: makeIdent(0xff, 1), Err: stub.UniqueError(0xbad01)},
-			&pkg.CureError{A: makeIdent(0xff, 9), Err: stub.UniqueError(0xbad09)},
-			&pkg.CureError{A: makeIdent(0xff, 0xf), Err: stub.UniqueError(0xbad0f)},
+			stub.UniqueError(0xbad00),
+			stub.UniqueError(0xbad01),
+			stub.UniqueError(0xbad09),
+			stub.UniqueError(0xbad0f),
 		}},
 	}
 	for _, tc := range testCases {
@@ -2022,7 +1988,19 @@ func TestDependencyCureError(t *testing.T) {
 				t.Errorf("Error:\n%s\nwant\n%s", got, tc.want)
 			}
 
-			if unwrap := tc.err.Unwrap(); !reflect.DeepEqual(unwrap, tc.unwrap) {
+			unwrap, unwrapM := tc.err.Unwrap(), make(map[error]struct{})
+			for _, a := range unwrap {
+				unwrapM[a] = struct{}{}
+			}
+
+			wantUnwrapM := make(map[error]struct{})
+			for _, a := range tc.unwrap {
+				wantUnwrapM[a] = struct{}{}
+			}
+
+			if len(unwrap) != len(unwrapM) ||
+				len(tc.unwrap) != len(wantUnwrapM) ||
+				!maps.Equal(unwrapM, wantUnwrapM) {
 				t.Errorf("Unwrap: %#v, want %#v", unwrap, tc.unwrap)
 			}
 		})
@@ -2055,19 +2033,21 @@ func (a earlyFailureF) Cure(*pkg.FContext) error {
 func BenchmarkEarlyDCE(b *testing.B) {
 	msg := message.New(log.New(os.Stderr, "dce: ", 0))
 	msg.SwapVerbose(testing.Verbose())
-	c, err := pkg.Open(b.Context(), msg, check.MustAbs(b.TempDir()), nil)
-	if err != nil {
-		b.Fatal(err)
-	}
-	_, _, err = c.Cure(earlyFailureF(8))
-	if !errors.Is(err, stub.UniqueError(0xcafe)) {
-		b.Fatalf("Cure: error = %v", err)
-	}
-	c.Close()
-	dce := err.(*pkg.DependencyCureError)
 
 	for b.Loop() {
-		dce.Unwrap()
+		b.StopTimer()
+		c, err := pkg.Open(b.Context(), msg, check.MustAbs(b.TempDir()), nil)
+		if err != nil {
+			b.Fatal(err)
+		}
+		b.StartTimer()
+		_, _, err = c.Cure(earlyFailureF(8))
+		b.StopTimer()
+		if !errors.Is(err, stub.UniqueError(0xcafe)) {
+			b.Fatalf("Cure: error = %v", err)
+		}
+		c.Close()
+		b.StartTimer()
 	}
 }