bake: fix map type checking to detect matrix property set to list

Signed-off-by: Justin Chadwell <me@jedevc.com>

bake/bake.go

@@ -820,7 +820,7 @@ func (t *Target) GetEvalContexts(ectx *hcl.EvalContext, block *hcl.Block, loadDe
 		return nil, err
 	}
 
-	if !value.CanIterateElements() {
+	if !value.Type().IsMapType() && !value.Type().IsObjectType() {
 		return nil, errors.Errorf("matrix must be a map")
 	}
 	matrix := value.AsValueMap()

bake/hcl_test.go

@@ -1051,6 +1051,14 @@ func TestHCLMatrixBadTypes(t *testing.T) {
 	_, err := ParseFile(dt, "docker-bake.hcl")
 	require.Error(t, err)
 
+	dt = []byte(`
+		target "default" {
+			matrix = ["test"]
+		}
+		`)
+	_, err = ParseFile(dt, "docker-bake.hcl")
+	require.Error(t, err)
+
 	dt = []byte(`
 		target "default" {
 			matrix = {
@@ -1061,6 +1069,16 @@ func TestHCLMatrixBadTypes(t *testing.T) {
 	_, err = ParseFile(dt, "docker-bake.hcl")
 	require.Error(t, err)
 
+	dt = []byte(`
+		target "default" {
+			matrix = {
+				1 = 2
+			}
+		}
+		`)
+	_, err = ParseFile(dt, "docker-bake.hcl")
+	require.Error(t, err)
+
 	dt = []byte(`
 		target "default" {
 			matrix = {