fix(platform-redirect): Keep the anchor of the next path

app/platform-redirect/page.tsx

@@ -7,7 +7,7 @@ import {SmartLink} from 'sentry-docs/components/smartLink';
 import {extractPlatforms, getDocsRootNode, nodeForPath} from 'sentry-docs/docTree';
 import {setServerContext} from 'sentry-docs/serverContext';
 
-import {sanitizeNext} from './utils';
+import {sanitizeNext, sanitizeNextHash} from './utils';
 
 export const metadata: Metadata = {
   robots: 'noindex',
@@ -29,6 +29,7 @@ export default async function Page(props: {
   }
 
   const pathname = sanitizeNext(next);
+  const hash = sanitizeNextHash(next);
   const isTracingAutomatedInstrumentation =
     pathname.replace(/\/$/, '') === '/tracing/instrumentation/automatic-instrumentation';
   const rootNode = await getDocsRootNode();
@@ -145,7 +146,7 @@ export default async function Page(props: {
       p => p.key === requestedPlatform?.toLowerCase()
     );
     if (validPlatform) {
-      return redirect(`${validPlatform.url}${pathname}`);
+      return redirect(`${validPlatform.url}${pathname}${hash}`);
     }
   }
 
@@ -167,7 +168,7 @@ export default async function Page(props: {
       <ul>
         {platformOrGuideList.map(p => (
           <li key={p.key} style={{marginLeft: p.shouldBeNested ? '20px' : '0'}}>
-            <SmartLink to={`${p.url}${pathname}`}>
+            <SmartLink to={`${p.url}${pathname}${hash}`}>
               <PlatformIcon
                 size={16}
                 platform={p.icon}

app/platform-redirect/utils.spec.ts

@@ -1,6 +1,6 @@
 import {describe, expect, it} from 'vitest';
 
-import {sanitizeNext} from './utils';
+import {sanitizeNext, sanitizeNextHash} from './utils';
 
 describe('sanitizeNext', () => {
   it('should return an empty string for external URLs', () => {
@@ -83,3 +83,35 @@ describe('sanitizeNext', () => {
     expect(sanitizeNext(input)).toBe(expectedOutput);
   });
 });
+
+describe('sanitizeNextHash', () => {
+  it('should return an empty string when there is no fragment', () => {
+    expect(sanitizeNextHash('/configuration/options/')).toBe('');
+    expect(sanitizeNextHash('/configuration/options/#')).toBe('');
+  });
+
+  it('should keep the fragment of an encoded next path', () => {
+    // `PlatformLink` encodes `next`, so the `#` arrives as `%23`
+    expect(sanitizeNextHash('%2Fconfiguration%2Foptions%2F%23ignoreErrors')).toBe(
+      '#ignoreErrors'
+    );
+    expect(sanitizeNextHash('/configuration/options/#tracing-options')).toBe(
+      '#tracing-options'
+    );
+  });
+
+  it('should keep dots and underscores used in option ids', () => {
+    expect(sanitizeNextHash('/configuration/options/#godot_logger.event_mask')).toBe(
+      '#godot_logger.event_mask'
+    );
+  });
+
+  it('should remove unsafe characters from the fragment', () => {
+    expect(sanitizeNextHash('/path/#a"><script>b')).toBe('#ascriptb');
+    expect(sanitizeNextHash('/path/#a/b?c=1')).toBe('#abc1');
+  });
+
+  it('should return an empty string for a malformed URI component', () => {
+    expect(sanitizeNextHash('/path/#%E0%A4%A')).toBe('');
+  });
+});

app/platform-redirect/utils.ts

@@ -35,3 +35,25 @@ export const sanitizeNext = (next: string) => {
 
   return pathname === '/' ? '' : pathname;
 };
+
+/**
+ * Returns the `#fragment` of `next` so the redirect can land on the same section,
+ * or an empty string if there is none. Only characters used in heading and option
+ * ids are kept.
+ */
+export const sanitizeNextHash = (next: string) => {
+  let decoded: string;
+  try {
+    decoded = decodeURIComponent(next);
+  } catch {
+    return '';
+  }
+
+  const hashIndex = decoded.indexOf('#');
+  if (hashIndex === -1) {
+    return '';
+  }
+
+  const fragment = decoded.slice(hashIndex + 1).replace(/[^\w\-.]/g, '');
+  return fragment ? `#${fragment}` : '';
+};