git: improve remote detection

The previous version had a few issues I got bitten by:

* it's on gitea/gitlab/github not necessary to have `.git` as suffix for
  a remote, i.e.

      git@github.com:org/repo

  is perfectly fine and because I wasn't that, all of my remotes were
  dismissed by this plugin.

* For forked repos I usually adhere to the convention to name my own
  fork's remote `origin` while the original repo's origin is called
  `upstream`[1]. This also means that if an issue is referenced in a
  file, it refers to the upstream's issue tracker.

  Accordingly I patched this part to prefer the upstream remote over the
  origin remote (if it exists).

  This is just a very bare-bone setup missing a few more important
  things:

  * on github at least you can also specify owner#issuename for issues
    in forks. This is still completely ignored.

  * the prefer remote X over Y should be at least configurable, perhaps
    it should be possible to do this on a per-project level.

  For me, the current state is good-enough to use and I figured I'd
  contribute my changes back here even though the patch is not perfect,
  perhaps they're useful as a base to improve this nice plugin.

[1] https://docs.github.com/en/get-started/quickstart/fork-a-repo

lua/gx/git.lua

@@ -4,17 +4,19 @@ local shell = require("gx.shell")
 
 M = {}
 
-local function parse_git_output(result)
-  if not result or table.getn(result) < 1 then
+local function parse_git_output(result, remote)
+  if not result then
     return
   end
 
-  local _, _, domain, repository = string.find(result[1], "^origin\t.*git@(.*%..*):(.*/.*).git")
+  local _, _, domain, repository = string.find(result, "^" .. remote .. "\t.*git@(.*%..*):(.*/.*) ")
+
   if domain and repository then
+    domain = domain:gsub("%.git", "")
     return "https://" .. domain .. "/" .. repository
   end
 
-  local _, _, url = string.find(result[1], "origin\t(.*)%s")
+  local _, _, url = string.find(result, remote .. "\t(.*)%s")
   if url then
     return url
   end
@@ -28,7 +30,16 @@ function M.get_remote_url()
     return
   end
 
-  local url = parse_git_output(result)
+  local url
+  for _, remote in ipairs({"upstream", "origin"}) do
+    for _, line in ipairs(result) do
+      url = parse_git_output(line, remote)
+      if url then
+        goto loopend
+      end
+    end
+  end
+  ::loopend::
   if not url then
     notfier.warn("No remote git repository found!")
   end