FIX: Subfolder replace should only affect URL prefix (#12135)

* FIX: Subfolder replace should only affect URL prefix

Issue was reported in https://meta.discourse.org/t/-/179504

* DEV: Test subfolder handling in get-url when called twice on the same path

app/assets/javascripts/discourse-common/addon/lib/get-url.js

@@ -1,9 +1,10 @@
-let cdn, baseUrl, baseUri;
+let cdn, baseUrl, baseUri, baseUriMatcher;
 let S3BaseUrl, S3CDN;
 
 export default function getURL(url) {
   if (baseUri === undefined) {
     baseUri = $('meta[name="discourse-base-uri"]').attr("content") || "";
+    baseUriMatcher = new RegExp(`^${baseUri}`);
   }
 
   if (!url) {
@@ -47,18 +48,23 @@ export function isAbsoluteURL(url) {
 }
 
 export function withoutPrefix(path) {
-  const rootURL = (!baseUri ? "/" : baseUri).replace(/\/$/, "");
+  if (!baseUri) {
-  return path.replace(rootURL, "");
+    return path;
+  } else {
+    return path.replace(baseUriMatcher, "");
+  }
 }
 
 export function setPrefix(configBaseUri) {
   baseUri = configBaseUri;
+  baseUriMatcher = new RegExp(`^${baseUri}`);
 }
 
 export function setupURL(configCdn, configBaseUrl, configBaseUri) {
   cdn = configCdn;
   baseUrl = configBaseUrl;
   baseUri = configBaseUri;
+  baseUriMatcher = new RegExp(`^${baseUri}`);
 }
 
 export function setupS3CDN(configS3BaseUrl, configS3CDN) {

app/assets/javascripts/discourse/tests/unit/lib/get-url-test.js

@@ -39,6 +39,43 @@ module("Unit | Utility | get-url", function () {
     assert.equal(withoutPrefix("/"), "/");
   });
 
+  test("withoutPrefix called multiple times on the same path", function (assert) {
+    setPrefix("/eviltrout");
+    assert.equal(withoutPrefix(withoutPrefix("/eviltrout/hello")), "/hello");
+    assert.equal(withoutPrefix(withoutPrefix("/eviltrout/")), "/");
+    assert.equal(withoutPrefix(withoutPrefix("/eviltrout")), "");
+
+    setPrefix("");
+    assert.equal(
+      withoutPrefix(withoutPrefix("/eviltrout/hello")),
+      "/eviltrout/hello"
+    );
+    assert.equal(withoutPrefix(withoutPrefix("/eviltrout")), "/eviltrout");
+    assert.equal(withoutPrefix(withoutPrefix("/")), "/");
+
+    setPrefix(null);
+    assert.equal(
+      withoutPrefix(withoutPrefix("/eviltrout/hello")),
+      "/eviltrout/hello"
+    );
+    assert.equal(withoutPrefix(withoutPrefix("/eviltrout")), "/eviltrout");
+    assert.equal(withoutPrefix(withoutPrefix("/")), "/");
+
+    setPrefix("/f");
+    assert.equal(
+      withoutPrefix(withoutPrefix("/f/t/falco-says-hello")),
+      "/t/falco-says-hello"
+    );
+    assert.equal(
+      withoutPrefix(withoutPrefix("/f/tag/fast-chain-food")),
+      "/tag/fast-chain-food"
+    );
+    assert.equal(
+      withoutPrefix(withoutPrefix("/f/u/falco/summary")),
+      "/u/falco/summary"
+    );
+  });
+
   test("getURL with empty paths", function (assert) {
     setupURL(null, "https://example.com", "/");
     assert.equal(getURL("/"), "/");