From 446e0f73219a442ba47f49c1fe732a1ccde64a30 Mon Sep 17 00:00:00 2001
From: Steven Hall <steven@gitbook.io>
Date: Wed, 23 Apr 2025 12:30:43 +0100
Subject: [PATCH 1/3] Improve error messages around undefined site sections.

---
 packages/gitbook-v2/src/lib/context.ts | 41 ++++++++++++++++++--------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/packages/gitbook-v2/src/lib/context.ts b/packages/gitbook-v2/src/lib/context.ts
index d25dd1946e..84c6231b91 100644
--- a/packages/gitbook-v2/src/lib/context.ts
+++ b/packages/gitbook-v2/src/lib/context.ts
@@ -19,6 +19,7 @@ import {
     getDataOrNull,
     throwIfDataError,
 } from '@v2/lib/data';
+import assertNever from 'assert-never';
 import { notFound } from 'next/navigation';
 import { assert } from 'ts-essentials';
 import { GITBOOK_URL } from './env';
@@ -242,19 +243,35 @@ export async function fetchSiteContextByIds(
         ? parseSiteSectionsAndGroups(siteStructure, ids.siteSection)
         : null;
 
-    const siteSpace = (
-        siteStructure.type === 'siteSpaces' && siteStructure.structure
-            ? siteStructure.structure
-            : sections?.current.siteSpaces
-    )?.find((siteSpace) => siteSpace.id === ids.siteSpace);
-    if (!siteSpace) {
-        throw new Error('Site space not found');
-    }
+    const { siteSpaces, siteSpace }: { siteSpaces: SiteSpace[]; siteSpace: SiteSpace } = (() => {
+        if (siteStructure.type === 'siteSpaces') {
+            const siteSpaces = siteStructure.structure;
+            const siteSpace = siteSpaces.find((siteSpace) => siteSpace.id === ids.siteSpace);
+
+            if (!siteSpace) {
+                throw new Error(`Site space "${ids.siteSpace}" not found in structure type="siteSpaces"`);
+            }
+
+            return { siteSpaces, siteSpace };
+        }
+
+        if (siteStructure.type === 'sections') {
+            assert(sections, `missing parsed sections siteStructure.type="sections" siteSection="${ids.siteSection}"`);
 
-    const siteSpaces =
-        siteStructure.type === 'siteSpaces'
-            ? siteStructure.structure
-            : (sections?.current.siteSpaces ?? []);
+            const currentSection = sections.current;
+            const siteSpaces = currentSection.siteSpaces;
+            const siteSpace = currentSection.siteSpaces.find((siteSpace) => siteSpace.id === ids.siteSpace);
+
+            if (!siteSpace) {
+                throw new Error(`Site space "${ids.siteSpace}" not found in structure type="sections" currentSection="${currentSection.id}"`);
+            }
+
+            return { siteSpaces, siteSpace };
+        }
+
+        // @ts-expect-error
+        assertNever(siteStructure, `cannot handle site structure of type ${siteStructure.type}`);
+    })();
 
     const customization = (() => {
         if (ids.siteSpace) {

From 40916b852377310bbe0984f459e08c7fc3b39429 Mon Sep 17 00:00:00 2001
From: Steven Hall <steven@gitbook.io>
Date: Wed, 23 Apr 2025 12:33:45 +0100
Subject: [PATCH 2/3] Message

---
 packages/gitbook-v2/src/lib/context.ts | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/packages/gitbook-v2/src/lib/context.ts b/packages/gitbook-v2/src/lib/context.ts
index 84c6231b91..7ef0f463b9 100644
--- a/packages/gitbook-v2/src/lib/context.ts
+++ b/packages/gitbook-v2/src/lib/context.ts
@@ -243,27 +243,37 @@ export async function fetchSiteContextByIds(
         ? parseSiteSectionsAndGroups(siteStructure, ids.siteSection)
         : null;
 
+    // Parse the current siteSpace and siteSpaces based on the site structure type.
     const { siteSpaces, siteSpace }: { siteSpaces: SiteSpace[]; siteSpace: SiteSpace } = (() => {
         if (siteStructure.type === 'siteSpaces') {
             const siteSpaces = siteStructure.structure;
             const siteSpace = siteSpaces.find((siteSpace) => siteSpace.id === ids.siteSpace);
 
             if (!siteSpace) {
-                throw new Error(`Site space "${ids.siteSpace}" not found in structure type="siteSpaces"`);
+                throw new Error(
+                    `Site space "${ids.siteSpace}" not found in structure type="siteSpaces"`
+                );
             }
 
             return { siteSpaces, siteSpace };
         }
 
         if (siteStructure.type === 'sections') {
-            assert(sections, `missing parsed sections siteStructure.type="sections" siteSection="${ids.siteSection}"`);
+            assert(
+                sections,
+                `cannot find site space "${ids.siteSpace}" because parsed sections are missing siteStructure.type="sections" siteSection="${ids.siteSection}"`
+            );
 
             const currentSection = sections.current;
             const siteSpaces = currentSection.siteSpaces;
-            const siteSpace = currentSection.siteSpaces.find((siteSpace) => siteSpace.id === ids.siteSpace);
+            const siteSpace = currentSection.siteSpaces.find(
+                (siteSpace) => siteSpace.id === ids.siteSpace
+            );
 
             if (!siteSpace) {
-                throw new Error(`Site space "${ids.siteSpace}" not found in structure type="sections" currentSection="${currentSection.id}"`);
+                throw new Error(
+                    `Site space "${ids.siteSpace}" not found in structure type="sections" currentSection="${currentSection.id}"`
+                );
             }
 
             return { siteSpaces, siteSpace };

From 5bf99cfcf3d5dfe1c5bb9fb1621b4f5b143a8c13 Mon Sep 17 00:00:00 2001
From: Steven Hall <steven@gitbook.io>
Date: Wed, 23 Apr 2025 12:34:08 +0100
Subject: [PATCH 3/3] changeset

---
 .changeset/soft-planes-talk.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/soft-planes-talk.md

diff --git a/.changeset/soft-planes-talk.md b/.changeset/soft-planes-talk.md
new file mode 100644
index 0000000000..d633d90dcd
--- /dev/null
+++ b/.changeset/soft-planes-talk.md
@@ -0,0 +1,5 @@
+---
+"gitbook-v2": patch
+---
+
+Improve error messages around undefined site sections.