internal/pkg: move concurrent cure implementation

This is useful independent of cure and might replace the Collect hack.

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

internal/pkg/pkg.go

@@ -1922,6 +1922,28 @@ func (c *Cache) tryExtern(
 	return checksum, err
 }
 
+// cureMany concurrently collects outcome of multiple [Artifact].
+func (c *Cache) cureMany(inputs []Artifact, r map[Artifact]cureRes) error {
+	var wg sync.WaitGroup
+	wg.Add(len(inputs))
+	res := make([]cureRes, len(inputs))
+	errs := make(DependencyCureError, 0, len(inputs))
+	var errsMu sync.Mutex
+	for i, d := range inputs {
+		pending := pendingArtifactDep{d, &res[i], &errs, &errsMu, &wg}
+		go pending.cure(c)
+	}
+	wg.Wait()
+
+	if len(errs) > 0 {
+		return &errs
+	}
+	for i, p := range res {
+		r[inputs[i]] = p
+	}
+	return nil
+}
+
 // cure implements Cure without acquiring a read lock on abortMu. cure must not
 // be entered during Abort.
 func (c *Cache) cure(a Artifact, curesExempt bool) (
@@ -2182,25 +2204,9 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 	case FloodArtifact:
 		inputs := a.Inputs()
 		f := FContext{t, make(map[Artifact]cureRes, len(inputs))}
-
+		if err = c.cureMany(inputs, f.inputs); err != nil {
-		var wg sync.WaitGroup
-		wg.Add(len(inputs))
-		res := make([]cureRes, len(inputs))
-		errs := make(DependencyCureError, 0, len(inputs))
-		var errsMu sync.Mutex
-		for i, d := range inputs {
-			pending := pendingArtifactDep{d, &res[i], &errs, &errsMu, &wg}
-			go pending.cure(c)
-		}
-		wg.Wait()
-
-		if len(errs) > 0 {
-			err = &errs
 			return
 		}
-		for i, p := range res {
-			f.inputs[inputs[i]] = p
-		}
 
 		sh := sha512.New384()
 		err = c.encode(sh, a, f.inputs)