git: support @{upstream} and @{push}

Inspired by https://github.com/tpope/vim-fugitive/issues/1482

.config/git/config

@@ -21,7 +21,11 @@
 [difftool "difft"]
 	cmd = difft "$LOCAL" "$REMOTE"
 [push]
-	default = simple
+	default = current
+[branch]
+	autoSetupMerge = inherit
+[remote]
+	pushDefault = origin
 [alias]
 	root = !pwd
 	assume   = update-index --assume-unchanged
@@ -30,9 +34,13 @@
 	lg = "log --color --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr)%C(bold blue)<%an>%Creset' --abbrev-commit"
 	po = push origin
 	pof = push origin --force-with-lease
-	ff = merge --ff-only @{upstream}
+	p = push
+	pf = push --force-with-lease
+	ff = merge --ff-only
 	roh = rebase origin/HEAD
 	rioh = rebase -i origin/HEAD
+	ru = rebase @{upstream}
+	riu = rebase -i @{upstream}
 	ca = commit --amend
 	smash = "!git add -u && git ca --no-edit && git pof"
 	reset-head = remote set-head origin -a

.config/nixpkgs/elvish/lib/prompt.elv

@@ -40,6 +40,14 @@ fn parse-git-branch {
   }
 }
 
+fn resolve-symbolic {|ref|
+  try {
+    put (git rev-parse --symbolic-full-name $ref 2> /dev/null)
+  } catch {
+    put $nil
+  }
+}
+
 fn parse-git-state {
   var git-revision = ''
   var git-branch = ''
@@ -47,15 +55,17 @@ fn parse-git-state {
   var git-staged = (num 0)
   var git-conflicts = (num 0)
   var git-untracked = (num 0)
-  var git-ahead = (num 0)
-  var git-behind = (num 0)
+  var git-ahead-upstream = (num 0)
+  var git-behind-upstream = (num 0)
+  var git-ahead-push = (num 0)
+  var git-behind-push = (num 0)
 
   git status --porcelain=v2 -b 2>/dev/null | each {|line|
     if (eq '#' $line[0]) {
       try {
         var match = (re:find '# branch.ab \+(\d+) -(\d+)' $line)
-        set git-ahead = (num $match[groups][1][text])
-        set git-behind = (num $match[groups][2][text])
+        set git-ahead-upstream = (num $match[groups][1][text])
+        set git-behind-upstream = (num $match[groups][2][text])
       } catch e {
         # noop
       }
@@ -93,16 +103,47 @@ fn parse-git-state {
       set git-ref-prefix = '@'
       set git-ref = $git-revision
     }
+  } else {
+    var git-push = (resolve-symbolic '@{push}')
+    var git-upstream = (resolve-symbolic '@{upstream}')
+    var git-origin-head = (resolve-symbolic origin/HEAD)
+
+    if (not-eq $nil $git-push) {
+      if (eq $git-push $git-upstream) {
+        # if push is the same as upstream, use the values from git status
+        set git-behind-push = $git-behind-upstream
+        set git-ahead-push = $git-ahead-upstream
+      } else {
+        # else calculate it ourselves
+        var behind ahead = (str:split "\t" (git rev-list --count --left-right '@{push}...HEAD'))
+        set git-behind-push = (num $behind)
+        set git-ahead-push = (num $ahead)
+      }
+    }
+
+    # if upstream is nil or the same as push, use origin/HEAD instead if
+    # present
+    if (and ^
+      (or (eq $git-push $git-upstream) (eq $nil $git-upstream)) ^
+      (not-eq $nil $git-origin-head) ^
+    ) {
+      var behind ahead = (str:split "\t" (git rev-list --count --left-right origin/HEAD...HEAD))
+      set git-behind-upstream = (num $behind)
+      set git-ahead-upstream = (num $ahead)
+    }
   }
 
   put '('
   put $git-ref-prefix
   styled $git-ref magenta bold
-  if (> $git-ahead 0) {
-    put '^'$git-ahead
+  if (> $git-ahead-push 0) {
+    put '^'$git-ahead-push
+  }
+  if (> $git-behind-push 0) {
+    put 'v'$git-behind-push
   }
-  if (> $git-behind 0) {
-    put 'v'$git-behind
+  if (> $git-behind-upstream 0) {
+    put '!'
   }
   put '|'
   if (> $git-staged 0) {

.config/nixpkgs/neovim/plugins/fugitive-origin-head.patch

@@ -6,7 +6,7 @@ index ce16048..2182c1b 100644
      if len(pull) && get(props, 'branch.ab') !~# ' -0$'
        call s:AddLogSection('Unpulled from ' . pull, [head . '..' . pull])
      endif
-+    if len(push)
++    if len(push) && push ==# pull
 +      call s:AddLogSection('Pushed to ' . push, ['origin/HEAD..' . push])
 +    endif