From 850dbdb0b6d17cce8afb3ccfb858d3e635389711 Mon Sep 17 00:00:00 2001
From: Virgil <virgil@lethean.io>
Date: Fri, 3 Apr 2026 20:08:13 +0000
Subject: [PATCH] feat(html): index repeated layout block ids

Co-Authored-By: Virgil <virgil@lethean.io>
---
 edge_test.go |  7 ++++++-
 layout.go    | 12 ++++++++----
 path.go      | 13 ++++++++++---
 path_test.go | 22 ++++++++++++----------
 4 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/edge_test.go b/edge_test.go
index d9ec689..30f2698 100644
--- a/edge_test.go
+++ b/edge_test.go
@@ -366,7 +366,7 @@ func TestLayout_InvalidVariant_MixedValidInvalid(t *testing.T) {
 func TestLayout_DuplicateVariantChars(t *testing.T) {
 	ctx := NewContext()
 
-	// "CCC" — C appears three times. Should render C slot content three times.
+	// "CCC" — C appears three times. Each occurrence should get its own block index.
 	layout := NewLayout("CCC").C(Raw("content"))
 	got := layout.Render(ctx)
 
@@ -374,6 +374,11 @@ func TestLayout_DuplicateVariantChars(t *testing.T) {
 	if count != 3 {
 		t.Errorf("CCC variant should render C slot 3 times, got %d occurrences in:\n%s", count, got)
 	}
+	for _, want := range []string{`data-block="C-0"`, `data-block="C-1"`, `data-block="C-2"`} {
+		if !strings.Contains(got, want) {
+			t.Errorf("CCC variant should contain %q in:\n%s", want, got)
+		}
+	}
 }
 
 func TestLayout_EmptySlots(t *testing.T) {
diff --git a/layout.go b/layout.go
index 452f71e..d0fd95c 100644
--- a/layout.go
+++ b/layout.go
@@ -138,9 +138,10 @@ func (l *Layout) setAttr(key, value string) {
 	l.attrs[key] = value
 }
 
-// blockID returns the deterministic data-block attribute value for a slot.
-func (l *Layout) blockID(slot byte) string {
-	return l.path + string(slot) + "-0"
+// blockID returns the deterministic data-block attribute value for a slot
+// occurrence within this layout variant.
+func (l *Layout) blockID(slot byte, index int) string {
+	return l.path + string(slot) + "-" + strconv.Itoa(index)
 }
 
 // layout.go: VariantError reports whether the layout variant string contained any invalid
@@ -171,6 +172,7 @@ func (l *Layout) Render(ctx *Context) string {
 
 	var b strings.Builder
 
+	slotCounts := make(map[byte]int)
 	for i := range len(l.variant) {
 		slot := l.variant[i]
 		children := l.slots[slot]
@@ -180,7 +182,9 @@ func (l *Layout) Render(ctx *Context) string {
 			continue
 		}
 
-		bid := l.blockID(slot)
+		index := slotCounts[slot]
+		slotCounts[slot] = index + 1
+		bid := l.blockID(slot, index)
 
 		b.WriteByte('<')
 		b.WriteString(escapeHTML(meta.tag))
diff --git a/path.go b/path.go
index f51641e..338ac68 100644
--- a/path.go
+++ b/path.go
@@ -10,7 +10,7 @@ func ParseBlockID(id string) []byte {
 	}
 
 	// Split on "-" and require the exact structural pattern:
-	// slot, 0, slot, 0, ...
+	// slot, numeric index, slot, numeric index, ...
 	var slots []byte
 	i := 0
 	for part := range strings.SplitSeq(id, "-") {
@@ -22,8 +22,15 @@ func ParseBlockID(id string) []byte {
 				return nil
 			}
 			slots = append(slots, part[0])
-		} else if part != "0" {
-			return nil
+		} else {
+			if part == "" {
+				return nil
+			}
+			for j := range len(part) {
+				if part[j] < '0' || part[j] > '9' {
+					return nil
+				}
+			}
 		}
 		i++
 	}
diff --git a/path_test.go b/path_test.go
index 15ef610..e80df1e 100644
--- a/path_test.go
+++ b/path_test.go
@@ -149,21 +149,22 @@ func TestNestedLayout_NilChild(t *testing.T) {
 
 func TestBlockID(t *testing.T) {
 	tests := []struct {
-		path string
-		slot byte
-		want string
+		path  string
+		slot  byte
+		index int
+		want  string
 	}{
-		{"", 'H', "H-0"},
-		{"L-0-", 'C', "L-0-C-0"},
-		{"C-0-C-0-", 'C', "C-0-C-0-C-0"},
-		{"", 'F', "F-0"},
+		{"", 'H', 0, "H-0"},
+		{"L-0-", 'C', 0, "L-0-C-0"},
+		{"C-0-C-0-", 'C', 0, "C-0-C-0-C-0"},
+		{"", 'F', 2, "F-2"},
 	}
 
 	for _, tt := range tests {
 		l := &Layout{path: tt.path}
-		got := l.blockID(tt.slot)
+		got := l.blockID(tt.slot, tt.index)
 		if got != tt.want {
-			t.Errorf("blockID(%q, %c) = %q, want %q", tt.path, tt.slot, got, tt.want)
+			t.Errorf("blockID(%q, %c, %d) = %q, want %q", tt.path, tt.slot, tt.index, got, tt.want)
 		}
 	}
 }
@@ -174,10 +175,11 @@ func TestParseBlockID(t *testing.T) {
 		want []byte
 	}{
 		{"L-0-C-0", []byte{'L', 'C'}},
+		{"C-0-C-1", []byte{'C', 'C'}},
 		{"H-0", []byte{'H'}},
 		{"C-0-C-0-C-0", []byte{'C', 'C', 'C'}},
 		{"", nil},
-		{"L-1-C-0", nil},
+		{"L-1-C-0", []byte{'L', 'C'}},
 		{"L-0-C", nil},
 		{"LL-0", nil},
 		{"X-0", nil},