buildflags: make work on go 1.22 by reverting rangefunc usage

Reverts the usage of rangefunc and attempts to keep the foundation of it
in for when we move to go 1.23. We have downstream dependencies that
aren't ready to move to go 1.23. We can likely move after go 1.24 is
released.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

go.mod

@@ -1,6 +1,6 @@
 module github.com/docker/buildx
 
-go 1.23.0
+go 1.22.0
 
 require (
 	github.com/Masterminds/semver/v3 v3.2.1

util/buildflags/attests_cty.go

@@ -22,16 +22,19 @@ func (e *Attests) FromCtyValue(in cty.Value, p cty.Path) error {
 	return p.NewErrorf("%s", convert.MismatchMessage(got, want))
 }
 
-func (e *Attests) fromCtyValue(in cty.Value, p cty.Path) error {
+func (e *Attests) fromCtyValue(in cty.Value, p cty.Path) (retErr error) {
 	*e = make([]*Attest, 0, in.LengthInt())
-	for value := range eachElement(in) {
+
+	yield := func(value cty.Value) bool {
 		entry := &Attest{}
-		if err := entry.FromCtyValue(value, p); err != nil {
+		if retErr = entry.FromCtyValue(value, p); retErr != nil {
-			return err
+			return false
 		}
 		*e = append(*e, entry)
+		return true
 	}
-	return nil
+	eachElement(in)(yield)
+	return retErr
 }
 
 func (e Attests) ToCtyValue() cty.Value {

util/buildflags/cache_cty.go

@@ -21,26 +21,30 @@ func (o *CacheOptions) FromCtyValue(in cty.Value, p cty.Path) error {
 	return p.NewErrorf("%s", convert.MismatchMessage(got, want))
 }
 
-func (o *CacheOptions) fromCtyValue(in cty.Value, p cty.Path) error {
+func (o *CacheOptions) fromCtyValue(in cty.Value, p cty.Path) (retErr error) {
 	*o = make([]*CacheOptionsEntry, 0, in.LengthInt())
-	for value := range eachElement(in) {
+
+	yield := func(value cty.Value) bool {
 		// Special handling for a string type to handle ref only format.
 		if value.Type() == cty.String {
-			entries, err := ParseCacheEntry([]string{value.AsString()})
+			var entries CacheOptions
-			if err != nil {
+			entries, retErr = ParseCacheEntry([]string{value.AsString()})
-				return err
+			if retErr != nil {
+				return false
 			}
 			*o = append(*o, entries...)
-			continue
+			return true
 		}
 
 		entry := &CacheOptionsEntry{}
-		if err := entry.FromCtyValue(value, p); err != nil {
+		if retErr = entry.FromCtyValue(value, p); retErr != nil {
-			return err
+			return false
 		}
 		*o = append(*o, entry)
+		return true
 	}
-	return nil
+	eachElement(in)(yield)
+	return retErr
 }
 
 func (o CacheOptions) ToCtyValue() cty.Value {

util/buildflags/export_cty.go

@@ -21,16 +21,19 @@ func (e *Exports) FromCtyValue(in cty.Value, p cty.Path) error {
 	return p.NewErrorf("%s", convert.MismatchMessage(got, want))
 }
 
-func (e *Exports) fromCtyValue(in cty.Value, p cty.Path) error {
+func (e *Exports) fromCtyValue(in cty.Value, p cty.Path) (retErr error) {
 	*e = make([]*ExportEntry, 0, in.LengthInt())
-	for value := range eachElement(in) {
+
+	yield := func(value cty.Value) bool {
 		entry := &ExportEntry{}
-		if err := entry.FromCtyValue(value, p); err != nil {
+		if retErr = entry.FromCtyValue(value, p); retErr != nil {
-			return err
+			return false
 		}
 		*e = append(*e, entry)
+		return true
 	}
-	return nil
+	eachElement(in)(yield)
+	return retErr
 }
 
 func (e Exports) ToCtyValue() cty.Value {

util/buildflags/secrets_cty.go

@@ -28,16 +28,19 @@ func (s *Secrets) FromCtyValue(in cty.Value, p cty.Path) error {
 	return p.NewErrorf("%s", convert.MismatchMessage(got, want))
 }
 
-func (s *Secrets) fromCtyValue(in cty.Value, p cty.Path) error {
+func (s *Secrets) fromCtyValue(in cty.Value, p cty.Path) (retErr error) {
 	*s = make([]*Secret, 0, in.LengthInt())
-	for value := range eachElement(in) {
+
+	yield := func(value cty.Value) bool {
 		entry := &Secret{}
-		if err := entry.FromCtyValue(value, p); err != nil {
+		if retErr = entry.FromCtyValue(value, p); retErr != nil {
-			return err
+			return false
 		}
 		*s = append(*s, entry)
+		return true
 	}
-	return nil
+	eachElement(in)(yield)
+	return retErr
 }
 
 func (s Secrets) ToCtyValue() cty.Value {

util/buildflags/ssh_cty.go

@@ -28,16 +28,19 @@ func (s *SSHKeys) FromCtyValue(in cty.Value, p cty.Path) error {
 	return p.NewErrorf("%s", convert.MismatchMessage(got, want))
 }
 
-func (s *SSHKeys) fromCtyValue(in cty.Value, p cty.Path) error {
+func (s *SSHKeys) fromCtyValue(in cty.Value, p cty.Path) (retErr error) {
 	*s = make([]*SSH, 0, in.LengthInt())
-	for value := range eachElement(in) {
+
+	yield := func(value cty.Value) bool {
 		entry := &SSH{}
-		if err := entry.FromCtyValue(value, p); err != nil {
+		if retErr = entry.FromCtyValue(value, p); retErr != nil {
-			return err
+			return false
 		}
 		*s = append(*s, entry)
+		return true
 	}
-	return nil
+	eachElement(in)(yield)
+	return retErr
 }
 
 func (s SSHKeys) ToCtyValue() cty.Value {

util/buildflags/utils.go

@@ -1,8 +1,6 @@
 package buildflags
 
 import (
-	"iter"
-
 	"github.com/zclconf/go-cty/cty"
 	"github.com/zclconf/go-cty/cty/gocty"
 )
@@ -57,7 +55,12 @@ func isEmptyOrUnknown(v cty.Value) bool {
 	return !v.IsKnown() || (v.Type() == cty.String && v.AsString() == "")
 }
 
-func eachElement(in cty.Value) iter.Seq[cty.Value] {
+// Seq is a temporary definition of iter.Seq until we are able to migrate
+// to using go1.23 as our minimum version. This can be removed when go1.24
+// is released and usages can be changed to use rangefunc.
+type Seq[V any] func(yield func(V) bool)
+
+func eachElement(in cty.Value) Seq[cty.Value] {
 	return func(yield func(v cty.Value) bool) {
 		for elem := in.ElementIterator(); elem.Next(); {
 			_, value := elem.Element()