internal/pkg: improve error resolution

This was taking way too long for early failures.

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

internal/pkg/pkg.go

@@ -1188,39 +1188,38 @@ func (e *CureError) Error() string { return e.Err.Error() }
 // A DependencyCureError wraps errors returned while curing dependencies.
 type DependencyCureError []*CureError
 
-// sort sorts underlying errors by their identifier.
-func (e *DependencyCureError) sort() {
-	var identBuf [2]ID
-	slices.SortFunc(*e, func(a, b *CureError) int {
-		identBuf[0], identBuf[1] = a.Ident.Value(), b.Ident.Value()
-		return slices.Compare(identBuf[0][:], identBuf[1][:])
-	})
+// unwrapM recursively expands underlying errors into a caller-supplied map.
+func (e *DependencyCureError) unwrapM(me map[unique.Handle[ID]]*CureError) {
+	for _, err := range *e {
+		if _e, ok := err.Err.(*DependencyCureError); ok {
+			_e.unwrapM(me)
+			continue
+		}
+		me[err.Ident] = err
+	}
 }
 
 // unwrap recursively expands and deduplicates underlying errors.
 func (e *DependencyCureError) unwrap() DependencyCureError {
-	errs := make(DependencyCureError, 0, len(*e))
-	for _, err := range *e {
-		if _e, ok := err.Err.(*DependencyCureError); ok {
-			errs = append(errs, _e.unwrap()...)
-			continue
-		}
-		errs = append(errs, err)
-	}
-	me := make(map[unique.Handle[ID]]*CureError, len(errs))
-	for _, err := range errs {
-		me[err.Ident] = err
-	}
-	return slices.AppendSeq(
+	me := make(map[unique.Handle[ID]]*CureError)
+	e.unwrapM(me)
+	errs := slices.AppendSeq(
 		make(DependencyCureError, 0, len(me)),
 		maps.Values(me),
 	)
+
+	var identBuf [2]ID
+	slices.SortFunc(errs, func(a, b *CureError) int {
+		identBuf[0], identBuf[1] = a.Ident.Value(), b.Ident.Value()
+		return slices.Compare(identBuf[0][:], identBuf[1][:])
+	})
+
+	return errs
 }
 
 // Unwrap returns a deduplicated slice of underlying errors.
 func (e *DependencyCureError) Unwrap() []error {
 	errs := e.unwrap()
-	errs.sort()
 	_errs := make([]error, len(errs))
 	for i, err := range errs {
 		_errs[i] = err
@@ -1231,7 +1230,6 @@ func (e *DependencyCureError) Unwrap() []error {
 // Error returns a user-facing multiline error message.
 func (e *DependencyCureError) Error() string {
 	errs := e.unwrap()
-	errs.sort()
 	if len(errs) == 0 {
 		return "invalid dependency cure outcome"
 	}

internal/pkg/pkg_test.go

@@ -15,6 +15,7 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"strconv"
 	"syscall"
 	"testing"
 	"unique"
@@ -1137,6 +1138,40 @@ func TestDependencyCureError(t *testing.T) {
 	}
 }
 
+// earlyFailureF is a [FloodArtifact] with a large dependency graph resulting in
+// a large [DependencyCureError].
+type earlyFailureF int
+
+func (earlyFailureF) Kind() pkg.Kind       { return pkg.KindExec }
+func (earlyFailureF) Params(*pkg.IContext) {}
+func (earlyFailureF) IsExclusive() bool    { return false }
+
+func (a earlyFailureF) Dependencies() []pkg.Artifact {
+	deps := make([]pkg.Artifact, a)
+	for i := range deps {
+		deps[i] = a - 1
+	}
+	return deps
+}
+
+func (a earlyFailureF) Cure(*pkg.FContext) error {
+	if a != 0 {
+		panic("unexpected cure on " + strconv.Itoa(int(a)))
+	}
+	return stub.UniqueError(0xcafe)
+}
+
+func TestDependencyCureErrorEarly(t *testing.T) {
+	checkWithCache(t, []cacheTestCase{
+		{"early", nil, func(t *testing.T, _ *check.Absolute, c *pkg.Cache) {
+			_, _, err := c.Cure(earlyFailureF(8))
+			if !errors.Is(err, stub.UniqueError(0xcafe)) {
+				t.Fatalf("Cure: error = %v", err)
+			}
+		}, pkg.MustDecode("E4vEZKhCcL2gPZ2Tt59FS3lDng-d_2SKa2i5G_RbDfwGn6EemptFaGLPUDiOa94C")},
+	})
+}
+
 func TestNew(t *testing.T) {
 	t.Parallel()