add arbitrary tag selection with *s

lua/dep.lua

@@ -479,16 +479,23 @@ local function sync(package, cb)
     return
   end
 
+  local function log_err(err)
+    logger:log("error", string.format("failed to update %s; reason: %s", package.id, err))
+  end
+
+  proc.git_resolve_branch(package.url, package.branch, function(err, branch)
+    if err then
+      log_err(err)
+      cb(err)
+    end
+    package.branch = branch
+
     if package.exists then
       if package.pin then
         cb()
         return
       end
 
-    local function log_err(err)
-      logger:log("error", string.format("failed to update %s; reason: %s", package.id, err))
-    end
-
       proc.git_rev_parse(package.dir, "HEAD", function(err, before)
         if err then
           log_err(before)
@@ -570,6 +577,7 @@ local function sync(package, cb)
         cb(err)
       end)
     end
+  end)
 end
 
 local function sync_list(list, on_complete)

lua/dep/proc.lua

@@ -71,4 +71,66 @@ function proc.git_checkout(dir, branch, commit, cb)
   end)
 end
 
+function proc.git_resolve_branch(url, branch, cb)
+  if string.match(branch or "", "*") ~= "*" then
+    cb(false, branch)
+    return
+  end
+  local buffer = {}
+
+  local function cb_output(_, data, _)
+    if data[1] ~= "" then
+      buffer = data
+    end
+  end
+
+  vim.fn.jobstart({
+    "git",
+    "ls-remote",
+    "--tags",
+    "--sort",
+    "v:refname",
+    url
+  }, {
+      cwd = nil,
+      env = { GIT_TERMINAL_PROMPT = 0 },
+      stdin = nil,
+      on_stdout = cb_output,
+      on_stderr = cb_output,
+      on_exit = function(_, exit_code, _)
+        if exit_code == 0 then
+          -- get a list of all versions
+          local versions = {}
+          for _, v in pairs(buffer) do
+            local s, e = string.find(v, "refs/tags/.+")
+            if not s or not e then
+              goto continue
+            end
+
+            local tag = string.sub(v, s, e)
+            tag = string.gsub(tag, "refs/tags/", "")
+            tag = string.gsub(tag, "%^{}", "")
+
+            table.insert(versions, tag)
+            ::continue::
+          end
+
+          -- match the chosen version against all versions
+          for i = #versions, 1, -1 do
+            if branch == "*" then
+              cb(false, versions[i])
+              return
+            else
+              local r = string.match(versions[i], branch)
+              if r then
+                cb(false, r)
+                return
+              end
+            end
+          end
+        end
+      end
+    })
+end
+
 return proc