fix(redirect): tolerate trailing slash difference if config is undefined

packages/docusaurus-plugin-client-redirects/src/__tests__/__snapshots__/collectRedirects.test.ts.snap

@@ -1,8 +1,9 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`collectRedirects throw if plugin option redirects contain invalid to paths 1`] = `
-"You are trying to create client-side redirections to paths that do not exist:
-- /this/path/does/not/exist2
+"You are trying to create client-side redirections to invalid paths.
+
+These paths are redirected to but do not exist:
 - /this/path/does/not/exist2
 
 Valid paths you can redirect to:
@@ -12,6 +13,22 @@ Valid paths you can redirect to:
 "
 `;
 
+exports[`collectRedirects throw if plugin option redirects contain to paths with mismatching trailing slash 1`] = `
+"You are trying to create client-side redirections to invalid paths.
+
+These paths do exist, but because you have explicitly set trailingSlash=false, you need to write the path without trailing slash:
+- /someExistingPath/
+"
+`;
+
+exports[`collectRedirects throw if plugin option redirects contain to paths with mismatching trailing slash 2`] = `
+"You are trying to create client-side redirections to invalid paths.
+
+These paths do exist, but because you have explicitly set trailingSlash=true, you need to write the path with trailing slash:
+- /someExistingPath
+"
+`;
+
 exports[`collectRedirects throws if redirect creator creates array of array redirect 1`] = `
 "Some created redirects are invalid:
 - {"from":["/fromPath"],"to":"/"} => Validation error: "from" must be a string

packages/docusaurus-plugin-client-redirects/src/__tests__/collectRedirects.test.ts

@@ -220,6 +220,69 @@ describe('collectRedirects', () => {
     ).toThrowErrorMatchingSnapshot();
   });
 
+  it('tolerates mismatched trailing slash if option is undefined', () => {
+    expect(
+      collectRedirects(
+        createTestPluginContext(
+          {
+            redirects: [
+              {
+                from: '/someLegacyPath',
+                to: '/somePath',
+              },
+            ],
+          },
+          ['/', '/somePath/'],
+          {trailingSlash: undefined},
+        ),
+        undefined,
+      ),
+    ).toEqual([
+      {
+        from: '/someLegacyPath',
+        to: '/somePath',
+      },
+    ]);
+  });
+
+  it('throw if plugin option redirects contain to paths with mismatching trailing slash', () => {
+    expect(() =>
+      collectRedirects(
+        createTestPluginContext(
+          {
+            redirects: [
+              {
+                from: '/someLegacyPath',
+                to: '/someExistingPath/',
+              },
+            ],
+          },
+          ['/', '/someExistingPath', '/anotherExistingPath'],
+          {trailingSlash: false},
+        ),
+        undefined,
+      ),
+    ).toThrowErrorMatchingSnapshot();
+
+    expect(() =>
+      collectRedirects(
+        createTestPluginContext(
+          {
+            redirects: [
+              {
+                from: '/someLegacyPath',
+                to: '/someExistingPath',
+              },
+            ],
+          },
+          ['/', '/someExistingPath/', '/anotherExistingPath/'],
+          {trailingSlash: true},
+        ),
+        undefined,
+      ),
+    ).toThrowErrorMatchingSnapshot();
+  });
+
   it('collects redirects with custom redirect creator', () => {
     expect(
       collectRedirects(

packages/docusaurus-plugin-client-redirects/src/collectRedirects.ts

@@ -7,6 +7,7 @@
 
 import _ from 'lodash';
 import logger from '@docusaurus/logger';
+import {addTrailingSlash, removeTrailingSlash} from '@docusaurus/utils';
 import {applyTrailingSlash} from '@docusaurus/utils-common';
 import {
   createFromExtensionsRedirects,
@@ -80,16 +81,61 @@ function validateCollectedRedirects(
 
   const allowedToPaths = pluginContext.relativeRoutesPaths;
   const toPaths = redirects.map((redirect) => redirect.to);
-  const illegalToPaths = _.difference(toPaths, allowedToPaths);
-  if (illegalToPaths.length > 0) {
-    throw new Error(
-      `You are trying to create client-side redirections to paths that do not exist:
-- ${illegalToPaths.join('\n- ')}
+  const trailingSlashConfig = pluginContext.siteConfig.trailingSlash;
+  // Key is the path, value is whether a valid toPath with a different trailing
+  // slash exists; if the key doesn't exist it means it's valid
+  const differByTrailSlash = new Map(toPaths.map((path) => [path, false]));
+  allowedToPaths.forEach((toPath) => {
+    if (differByTrailSlash.has(toPath)) {
+      differByTrailSlash.delete(toPath);
+      return;
+    }
+    if (differByTrailSlash.has(removeTrailingSlash(toPath))) {
+      if (trailingSlashConfig === true) {
+        differByTrailSlash.set(removeTrailingSlash(toPath), true);
+      } else {
+        differByTrailSlash.delete(removeTrailingSlash(toPath));
+      }
+    } else if (differByTrailSlash.has(addTrailingSlash(toPath))) {
+      if (trailingSlashConfig === false) {
+        differByTrailSlash.set(addTrailingSlash(toPath), true);
+      } else {
+        differByTrailSlash.delete(addTrailingSlash(toPath));
+      }
+    }
+  });
+  if (differByTrailSlash.size > 0) {
+    console.log(differByTrailSlash);
+    const errors = Array.from(differByTrailSlash.entries());
+
+    let message =
+      'You are trying to create client-side redirections to invalid paths.\n';
+
+    const [trailingSlashIssues, invalidPaths] = _.partition(
+      errors,
+      ([, differ]) => differ,
+    );
+
+    if (trailingSlashIssues.length) {
+      message += `
+These paths do exist, but because you have explicitly set trailingSlash=${trailingSlashConfig}, you need to write the path ${
+        trailingSlashConfig ? 'with trailing slash' : 'without trailing slash'
+      }:
+- ${trailingSlashIssues.map(([p]) => p).join('\n- ')}
+`;
+    }
+
+    if (invalidPaths.length) {
+      message += `
+These paths are redirected to but do not exist:
+- ${invalidPaths.map(([p]) => p).join('\n- ')}
 
 Valid paths you can redirect to:
 - ${allowedToPaths.join('\n- ')}
-`,
-    );
+`;
+    }
+
+    throw new Error(message);
   }
 }