Melpa - 'Failed to download melpa'

Question

I am on a fresh install of emacs 26.3, and I have the following in my init.el:

(require 'package)
(add-to-list 'package-archives
             '("melpa", "http://melpa.org/packages/") t)
(package-initialize)

When I go to refresh the package list (M-x package-refresh-contents) I encounter the following error:

  string-match("\\`https?:" ((\, "http://melpa.org/packages/")) nil)
  package--download-one-archive(("melpa" (\, "http://melpa.org/packages/")) "archive-contents" t)
  package--download-and-read-archives(t)
  package-refresh-contents(t)
  package-menu-refresh()
  package-list-packages(nil)
  funcall-interactively(package-list-packages nil)
  call-interactively(package-list-packages record nil)
  command-execute(package-list-packages record)
  execute-extended-command(nil "package-list-packages" "package-lis")
  funcall-interactively(execute-extended-command nil "package-list-packages" "package-lis")
  call-interactively(execute-extended-command nil nil)
  command-execute(execute-extended-command)

What is happening and why doesn't this work? I have seen some chatter on related issues that

(setq gnutls-algorithm-priority "NORMAL:-VERS-TLS1.3")

before (package-initialize) should resolve this issue, but it doesn't.

Answer 1

The error seems to be saying that ((\, "http://melpa.org/packages/")) doesn't match the regex

"\`https?:"

Let's look at that value, the one being added to package-archives:

'("melpa", "http://melpa.org/packages/")

If we put this into IELM, let's see what we get:

ELISP> '("melpa", "http://melpa.org/packages/")
("melpa"
 (\, "http://melpa.org/packages/"))

Oh! This is not what we expect! The cdr of this list is a proper list (we want a string), and that has a comma as the first character.

What happened here? What is each element of package-archives supposed to be?

package-archives is a variable defined in ‘package.el’.

Each element has the form (ID . LOCATION).

A period instead of a comma makes this a single cons cell, and not a proper list. The proper code is:

(add-to-list 'package-archives
             '("melpa" . "https://melpa.org/packages/") t)