site: fixed .md/lyng code display

lynglib/src/commonMain/kotlin/net/sergeych/lyng/highlight/SimpleLyngHighlighter.kt

@@ -117,6 +117,28 @@ private fun mergeAdjacent(spans: List<HighlightSpan>): List<HighlightSpan> {
     return out
 }
 
+/**
+ * The parser expands interpolated strings into expression-like token streams whose
+ * synthetic tokens share source positions with the original string. Keep the
+ * widest source span at each offset and drop nested overlaps so renderers can
+ * rely on the public non-overlapping span contract.
+ */
+private fun removeOverlappingSpans(spans: List<HighlightSpan>): List<HighlightSpan> {
+    if (spans.size < 2) return spans
+    val sorted = spans.sortedWith(
+        compareBy<HighlightSpan> { it.range.start }
+            .thenByDescending { it.range.endExclusive - it.range.start }
+    )
+    val out = ArrayList<HighlightSpan>(sorted.size)
+    var coveredUntil = -1
+    for (span in sorted) {
+        if (span.range.start < coveredUntil) continue
+        out += span
+        coveredUntil = span.range.endExclusive
+    }
+    return out
+}
+
 /** Simple highlighter using the existing Lyng lexer (no incremental support yet). */
 class SimpleLyngHighlighter : LyngHighlighter {
     override fun highlight(text: String): List<HighlightSpan> {
@@ -170,8 +192,8 @@ class SimpleLyngHighlighter : LyngHighlighter {
         val overridden = applyEnumConstantHeuristics(text, src, tokens, raw)
         // Adjust single-line comment spans to extend till EOL to compensate for lexer offset/length quirks
         val adjusted = extendSingleLineCommentsToEol(text, overridden)
-        // Spans are in order; merge adjacent of the same kind for compactness
-        return mergeAdjacent(adjusted)
+        // Normalize spans, then merge adjacent spans of the same kind for compactness.
+        return mergeAdjacent(removeOverlappingSpans(adjusted))
     }
 }
 

lynglib/src/commonTest/kotlin/net/sergeych/lyng/highlight/HighlightMappingTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@
 package net.sergeych.lyng.highlight
 
 import kotlin.test.Test
+import kotlin.test.assertEquals
 import kotlin.test.assertTrue
 
 class HighlightMappingTest {
@@ -72,6 +73,38 @@ class HighlightMappingTest {
         assertTrue(labeled.any { it.first == "\"s\"" && it.second == HighlightKind.String })
     }
 
+    @Test
+    fun interpolatedStringSpansDoNotOverlap() {
+        val text = """p { +"Path: ${'$'}{request.path}" }"""
+        val spans = SimpleLyngHighlighter().highlight(text)
+        spans.zipWithNext().forEach { (a, b) ->
+            assertTrue(
+                a.range.endExclusive <= b.range.start,
+                "Highlight spans must not overlap: $a then $b in $spans"
+            )
+        }
+        assertTrue(
+            spansToLabeled(text, spans).any {
+                it.first == "\"Path: ${'$'}{request.path}\"" && it.second == HighlightKind.String
+            }
+        )
+    }
+
+    @Test
+    fun interpolatedStringRenderingDoesNotDuplicateText() {
+        val text = """p { +"Path: ${'$'}{request.path}" }"""
+        val rendered = buildString {
+            var pos = 0
+            for (span in SimpleLyngHighlighter().highlight(text)) {
+                if (span.range.start > pos) append(text.substring(pos, span.range.start))
+                append(text.substring(span.range.start, span.range.endExclusive))
+                pos = span.range.endExclusive
+            }
+            if (pos < text.length) append(text.substring(pos))
+        }
+        assertEquals(text, rendered)
+    }
+
     @Test
     fun commentsHighlighted() {
         val text = "// line\n/* block */"