Use GHCup vanilla and prereleases channels by default

Author: andreasabel

dist/index.js

@@ -354,13 +354,13 @@ async function ghcupBin(os: OS, arch: Arch): Promise<string> {
 }
 
 export async function addGhcupReleaseChannel(
-  channel: URL,
+  channel: string,
   os: OS,
   arch: Arch
 ): Promise<void> {
   core.info(`Adding ghcup release channel: ${channel}`);
   const bin = await ghcupBin(os, arch);
-  await exec(bin, ['config', 'add-release-channel', channel.toString()]);
+  await exec(bin, ['config', 'add-release-channel', channel]);
 }
 
 async function ghcup(

lib/installer.d.ts

@@ -40,9 +40,14 @@ export default async function run(
     core.debug(`run: os     = ${JSON.stringify(os)}`);
     core.debug(`run: opts   = ${JSON.stringify(opts)}`);
 
+    // Andreas Abel, 2026-01-01, https://github.com/haskell-actions/setup/issues/78
+    // Add ghcup vanilla and prereleases channels by default.
+    addGhcupReleaseChannel('vanilla', os, arch);
+    addGhcupReleaseChannel('prereleases', os, arch);
+
     if (opts.ghcup.releaseChannel) {
       await core.group(`Preparing ghcup environment`, async () =>
-        addGhcupReleaseChannel(opts.ghcup.releaseChannel!, os, arch)
+        addGhcupReleaseChannel(opts.ghcup.releaseChannel!.toString(), os, arch)
       );
     }