Fix dead search-index links in single HTML layout

FirstClassErrors.GenDoc.UnitTests/HtmlErrorDocumentationRendererTests.cs

@@ -154,6 +154,34 @@ public void TheSplitLayoutProducesAHomePageAndOnePagePerError() {
         Check.That(page).Contains("../index.html");
     }
 
+    [Fact(DisplayName = "The split search index links each error to its own page.")]
+    public void TheSplitSearchIndexLinksEachErrorToItsPage() {
+        // Exercise
+        string json = ContentOf(RenderSplit(TemperatureError(), EmailError()), "assets/search-index.json");
+
+        // Verify: in split, the errors/… pages exist, so the index points at them.
+        Check.That(json).Contains("\"href\": \"errors/TEMPERATURE_BELOW_ABSOLUTE_ZERO.html\"");
+        Check.That(json).Contains("\"href\": \"errors/INVALID_EMAIL.html\"");
+    }
+
+    [Fact(DisplayName = "The single search index links each error to its in-page anchor, not a missing page.")]
+    public void TheSingleSearchIndexLinksEachErrorToItsInPageAnchor() {
+        // Exercise
+        IReadOnlyList<RenderedDocument> documents = RenderSingle(TemperatureError(), EmailError());
+        string                         json       = ContentOf(documents, "assets/search-index.json");
+
+        // Verify: single emits only index.html (no errors/… files), so the index must point at #err-… anchors there.
+        Check.That(documents.Select(d => d.RelativePath)).Not.Contains("errors/TEMPERATURE_BELOW_ABSOLUTE_ZERO.html");
+        Check.That(json).Contains("\"href\": \"index.html#err-TEMPERATURE_BELOW_ABSOLUTE_ZERO\"");
+        Check.That(json).Contains("\"href\": \"index.html#err-INVALID_EMAIL\"");
+        Check.That(json).Not.Contains("\"href\": \"errors/");
+
+        // The referenced anchors actually exist in the single page.
+        string html = ContentOf(documents, "index.html");
+        Check.That(html).Contains("id=\"err-TEMPERATURE_BELOW_ABSOLUTE_ZERO\"");
+        Check.That(html).Contains("id=\"err-INVALID_EMAIL\"");
+    }
+
     [Fact(DisplayName = "The HTML renderer escapes catalog content.")]
     public void TheHtmlRendererEscapesCatalogContent() {
         // Setup: a title and a message carrying HTML metacharacters.

FirstClassErrors.GenDoc/Rendering/HtmlErrorDocumentationRenderer.cs

@@ -51,7 +51,7 @@ public IReadOnlyList<RenderedDocument> Render(IEnumerable<ErrorDocumentation> ca
 
         // The CSS and JS are inlined into every page (see BuildPage) so each file is self-contained and stays styled
         // even when opened on its own. Only the search index remains an external asset, for external tooling.
-        documents.Add(new RenderedDocument("assets/search-index.json", BuildSearchIndex(entries)));
+        documents.Add(new RenderedDocument("assets/search-index.json", BuildSearchIndex(entries, split)));
 
         return documents;
     }
@@ -381,19 +381,22 @@ private static string UniqueAnchor(string source, HashSet<string> used) {
         return anchor;
     }
 
-    private static string BuildSearchIndex(IReadOnlyList<Entry> entries) {
+    private static string BuildSearchIndex(IReadOnlyList<Entry> entries, bool split) {
         // A curated, deterministic index for external tooling. In-page search uses the embedded row data instead,
         // so it keeps working when the site is opened from file:// (where fetch of a local JSON is often blocked).
+        // The href must match the actual layout: one page per error in split, an in-page anchor in single (where
+        // there is no errors/… file — the errors are #err-… anchors inside index.html).
         StringBuilder json = new();
         json.Append("[\n");
         for (int index = 0; index < entries.Count; index++) {
-            Entry entry = entries[index];
+            Entry  entry = entries[index];
+            string href  = split ? $"errors/{entry.FileName}" : $"index.html#err-{entry.Anchor}";
             json.Append("  {\n");
             json.Append($"    \"code\": \"{JsonString(entry.Code)}\",\n");
             json.Append($"    \"title\": \"{JsonString(entry.Title)}\",\n");
             json.Append($"    \"summary\": \"{JsonString(entry.Summary)}\",\n");
             json.Append($"    \"source\": \"{JsonString(entry.Source ?? string.Empty)}\",\n");
-            json.Append($"    \"href\": \"errors/{JsonString(entry.FileName)}\",\n");
+            json.Append($"    \"href\": \"{JsonString(href)}\",\n");
             json.Append($"    \"text\": \"{JsonString(entry.SearchText)}\"\n");
             json.Append(index == entries.Count - 1 ? "  }\n" : "  },\n");
         }