Keep trailing slash when building http routes

.chronus/changes/http-trailing-slash-2024-6-2-23-8-57.md

@@ -0,0 +1,15 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: breaking
+packages:
+  - "@typespec/http"
+---
+
+Keep trailing slash when building http routes, this is breaking if you used to have `@route()` ending with `/`.
+
+  | TypeSpec                                                         | Before            | After              |
+  | ---------------------------------------------------------------- | ----------------- | ------------------ |
+  | `@route("users/")`                                               | `users`           | `users/`           |
+  | `@route("users")`                                                | `users`           | `users`            |
+  | on interface `@route("users/")` and on op `@route("addresses/")` | `users/addresses` | `users/addresses/` |
+  | on interface `@route("users/")` and on op `@route("addresses")`  | `users/addresses` | `users/addresses`  |

packages/http/src/route.ts

@@ -25,28 +25,32 @@ import { extractParamsFromPath } from "./utils.js";
 // The set of allowed segment separator characters
 const AllowedSegmentSeparators = ["/", ":"];
 
-function normalizeFragment(fragment: string) {
+function normalizeFragment(fragment: string, trimLast = false) {
   if (fragment.length > 0 && AllowedSegmentSeparators.indexOf(fragment[0]) < 0) {
     // Insert the default separator
     fragment = `/${fragment}`;
   }
 
-  // Trim any trailing slash
-  return fragment.replace(/\/$/g, "");
+  if (trimLast && fragment[fragment.length - 1] === "/") {
+    return fragment.slice(0, -1);
+  }
+  return fragment;
+}
+
+function joinPathSegments(rest: string[]) {
+  let current = "";
+  for (const [index, segment] of rest.entries()) {
+    current += normalizeFragment(segment, index < rest.length - 1);
+  }
+  return current;
 }
 
 function buildPath(pathFragments: string[]) {
   // Join all fragments with leading and trailing slashes trimmed
-  const path =
-    pathFragments.length === 0
-      ? "/"
-      : pathFragments
-          .map(normalizeFragment)
-          .filter((x) => x !== "")
-          .join("");
+  const path = pathFragments.length === 0 ? "/" : joinPathSegments(pathFragments);
 
   // The final path must start with a '/'
-  return path.length > 0 && path[0] === "/" ? path : `/${path}`;
+  return path[0] === "/" ? path : `/${path}`;
 }
 
 export function resolvePathAndParameters(

packages/http/test/routes.test.ts

@@ -154,14 +154,14 @@ describe("http: routes", () => {
   describe("@route path parameters mapping", () => {
     it("maps route interpolated params to the operation param", async () => {
       const routes = await getRoutesFor(
-        `@route("/foo/{myParam}/") op test(@path myParam: string): void;`
+        `@route("/foo/{myParam}") op test(@path myParam: string): void;`
       );
       deepStrictEqual(routes, [{ verb: "get", path: "/foo/{myParam}", params: ["myParam"] }]);
     });
 
     it("maps route interpolated params to the operation param when operation spread items", async () => {
       const routes = await getRoutesFor(
-        `@route("/foo/{myParam}/") op test(@path myParam: string, ...Record<string>): void;`
+        `@route("/foo/{myParam}") op test(@path myParam: string, ...Record<string>): void;`
       );
       deepStrictEqual(routes, [{ verb: "post", path: "/foo/{myParam}", params: ["myParam"] }]);
     });
@@ -280,6 +280,29 @@ describe("http: routes", () => {
     deepStrictEqual(routes, [{ verb: "get", path: "/", params: [] }]);
   });
 
+  it("keeps trailing / at the end of the route", async () => {
+    const routes = await getRoutesFor(
+      `
+      @route("/foo/") op index(): void;
+      `
+    );
+
+    deepStrictEqual(routes, [{ verb: "get", path: "/foo/", params: [] }]);
+  });
+
+  it("merge trailing and leading / when combining container path", async () => {
+    const routes = await getRoutesFor(
+      `
+      @route("/foo/")
+      interface Foo {
+        @route("/bar/") op index(): void;
+      }
+      `
+    );
+
+    deepStrictEqual(routes, [{ verb: "get", path: "/foo/bar/", params: [] }]);
+  });
+
   it("join / route segments correctly", async () => {
     const routes = await getRoutesFor(
       `