feat(html): export layout variant diagnostics

Co-Authored-By: Virgil <virgil@lethean.io>

layout.go

@@ -70,7 +70,7 @@ func ValidateLayoutVariant(variant string) error {
 	if len(invalidSlots) == 0 {
 		return nil
 	}
-	return &layoutVariantError{
+	return &LayoutVariantError{
 		variant:          variant,
 		invalidSlots:     invalidSlots,
 		invalidPositions: invalidPositions,
@@ -200,13 +200,13 @@ func (l *Layout) Render(ctx *Context) string {
 	return b.String()
 }
 
-type layoutVariantError struct {
+type LayoutVariantError struct {
 	variant          string
 	invalidSlots     []byte
 	invalidPositions []int
 }
 
-func (e *layoutVariantError) Error() string {
+func (e *LayoutVariantError) Error() string {
 	if e == nil {
 		return ErrInvalidLayoutVariant.Error()
 	}
@@ -237,13 +237,13 @@ func (e *layoutVariantError) Error() string {
 	return b.String()
 }
 
-func (e *layoutVariantError) Unwrap() error {
+func (e *LayoutVariantError) Unwrap() error {
 	return ErrInvalidLayoutVariant
 }
 
 // InvalidSlots returns a copy of the invalid slot characters that were present
 // in the original variant string.
-func (e *layoutVariantError) InvalidSlots() []byte {
+func (e *LayoutVariantError) InvalidSlots() []byte {
 	if e == nil || len(e.invalidSlots) == 0 {
 		return nil
 	}
@@ -252,7 +252,7 @@ func (e *layoutVariantError) InvalidSlots() []byte {
 
 // InvalidPositions returns a copy of the 1-based positions of the invalid slot
 // characters in the original variant string.
-func (e *layoutVariantError) InvalidPositions() []int {
+func (e *LayoutVariantError) InvalidPositions() []int {
 	if e == nil || len(e.invalidPositions) == 0 {
 		return nil
 	}

layout_external_test.go

@@ -0,0 +1,28 @@
+package html_test
+
+import (
+	"errors"
+	"testing"
+
+	html "dappco.re/go/core/html"
+)
+
+func TestValidateLayoutVariant_ExportsPositions(t *testing.T) {
+	err := html.ValidateLayoutVariant("H1X?")
+	if err == nil {
+		t.Fatal("ValidateLayoutVariant returned nil, want error")
+	}
+
+	var variantErr *html.LayoutVariantError
+	if !errors.As(err, &variantErr) {
+		t.Fatalf("errors.As(%T) failed, want *html.LayoutVariantError", err)
+	}
+
+	if got := string(variantErr.InvalidSlots()); got != "1X?" {
+		t.Fatalf("InvalidSlots() = %q, want %q", got, "1X?")
+	}
+
+	if got := variantErr.InvalidPositions(); len(got) != 3 || got[0] != 2 || got[1] != 3 || got[2] != 4 {
+		t.Fatalf("InvalidPositions() = %v, want %v", got, []int{2, 3, 4})
+	}
+}

layout_test.go

@@ -188,7 +188,7 @@ func TestLayout_VariantError(t *testing.T) {
 			variant:       "H1X?",
 			wantErr:       true,
 			wantErrString: "html: invalid layout variant H1X? (invalid slots: '1' at position 2, 'X' at position 3, '?' at position 4)",
-			wantRender: `<header role="banner" data-block="H-0">header</header>`,
+			wantRender:    `<header role="banner" data-block="H-0">header</header>`,
 		},
 	}
 
@@ -207,7 +207,7 @@ func TestLayout_VariantError(t *testing.T) {
 				if got := layout.VariantError().Error(); got != tt.wantErrString {
 					t.Fatalf("VariantError().Error() = %q, want %q", got, tt.wantErrString)
 				}
-				if err, ok := layout.VariantError().(*layoutVariantError); ok {
+				if err, ok := layout.VariantError().(*LayoutVariantError); ok {
 					switch tt.variant {
 					case "HXC":
 						if got := string(err.InvalidSlots()); got != "X" {