Reject shrinking disk during YAML validation

cmd/limactl/edit.go

@@ -118,13 +118,13 @@ func editAction(cmd *cobra.Command, args []string) error {
 		return err
 	}
 	if err := limayaml.Validate(y, true); err != nil {
-		rejectedYAML := "lima.REJECTED.yaml"
-		if writeErr := os.WriteFile(rejectedYAML, yBytes, 0o644); writeErr != nil {
-			return fmt.Errorf("the YAML is invalid, attempted to save the buffer as %q but failed: %w: %w", rejectedYAML, writeErr, err)
-		}
-		// TODO: may need to support editing the rejected YAML
-		return fmt.Errorf("the YAML is invalid, saved the buffer as %q: %w", rejectedYAML, err)
+		return saveRejectedYAML(yBytes, err)
+	}
+
+	if err := limayaml.ValidateYAMLAgainstLatestConfig(yBytes, yContent); err != nil {
+		return saveRejectedYAML(yBytes, err)
 	}
+
 	if err := os.WriteFile(filePath, yBytes, 0o644); err != nil {
 		return err
 	}
@@ -171,3 +171,13 @@ func askWhetherToStart() (bool, error) {
 func editBashComplete(cmd *cobra.Command, _ []string, _ string) ([]string, cobra.ShellCompDirective) {
 	return bashCompleteInstanceNames(cmd)
 }
+
+// saveRejectedYAML writes the rejected config and returns an error.
+func saveRejectedYAML(y []byte, origErr error) error {
+	rejectedYAML := "lima.REJECTED.yaml"
+	if writeErr := os.WriteFile(rejectedYAML, y, 0o644); writeErr != nil {
+		return fmt.Errorf("the YAML is invalid, attempted to save the buffer as %q but failed: %w", rejectedYAML, errors.Join(writeErr, origErr))
+	}
+	// TODO: may need to support editing the rejected YAML
+	return fmt.Errorf("the YAML is invalid, saved the buffer as %q: %w", rejectedYAML, origErr)
+}

pkg/limayaml/validate.go

@@ -610,3 +610,40 @@ func warnExperimental(y *LimaYAML) {
 		logrus.Warn("`mountInotify` is experimental")
 	}
 }
+
+// ValidateYAMLAgainstLatestConfig validates the values between the latest YAML and the updated(New) YAML.
+// This validates configuration rules that disallow certain changes, such as shrinking the disk.
+func ValidateYAMLAgainstLatestConfig(yNew, yLatest []byte) error {
+	var n LimaYAML
+
+	// Load the latest YAML and fill in defaults
+	l, err := LoadWithWarnings(yLatest, "")
+	if err != nil {
+		return err
+	}
+	if err := Unmarshal(yNew, &n, "Unmarshal new YAML bytes"); err != nil {
+		return err
+	}
+
+	// Handle editing the template without a disk value
+	if n.Disk == nil || l.Disk == nil {
+		return nil
+	}
+
+	// Disk value must be provided, as it is required when creating an instance.
+	nDisk, err := units.RAMInBytes(*n.Disk)
+	if err != nil {
+		return err
+	}
+	lDisk, err := units.RAMInBytes(*l.Disk)
+	if err != nil {
+		return err
+	}
+
+	// Reject shrinking disk
+	if nDisk < lDisk {
+		return fmt.Errorf("field `disk`: shrinking the disk (%v --> %v) is not supported", *l.Disk, *n.Disk)
+	}
+
+	return nil
+}

pkg/limayaml/validate_test.go

@@ -4,6 +4,7 @@
 package limayaml
 
 import (
+	"errors"
 	"testing"
 
 	"gotest.tools/v3/assert"
@@ -264,3 +265,55 @@ provision:
 		"field `provision[0].mode` must one of \"system\", \"user\", \"boot\", \"data\", \"dependency\", or \"ansible\"\n"+
 		"field `provision[1].path` must not be empty when mode is \"data\"")
 }
+
+func TestValidateYAMLAgainstLatestConfig(t *testing.T) {
+	tests := []struct {
+		name    string
+		yNew    string
+		yLatest string
+		wantErr error
+	}{
+		{
+			name:    "Valid disk size unchanged",
+			yNew:    `disk: 100GiB`,
+			yLatest: `disk: 100GiB`,
+		},
+		{
+			name:    "Valid disk size increased",
+			yNew:    `disk: 200GiB`,
+			yLatest: `disk: 100GiB`,
+		},
+		{
+			name:    "No disk field in both YAMLs",
+			yNew:    ``,
+			yLatest: ``,
+		},
+		{
+			name:    "No disk field in new YAMLs",
+			yNew:    ``,
+			yLatest: `disk: 100GiB`,
+		},
+		{
+			name:    "No disk field in latest YAMLs",
+			yNew:    `disk: 100GiB`,
+			yLatest: ``,
+		},
+		{
+			name:    "Disk size shrunk",
+			yNew:    `disk: 50GiB`,
+			yLatest: `disk: 100GiB`,
+			wantErr: errors.New("field `disk`: shrinking the disk (100GiB --> 50GiB) is not supported"),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := ValidateYAMLAgainstLatestConfig([]byte(tt.yNew), []byte(tt.yLatest))
+			if tt.wantErr == nil {
+				assert.NilError(t, err)
+			} else {
+				assert.Error(t, err, tt.wantErr.Error())
+			}
+		})
+	}
+}