feat: Add health check.

Moves dependency checking from the bootstrapping step to the new health
check.

The health check will validate the state of plugin dependencies as well
as external dependencies. Run the health check with:

`:checkhealth diffview`

(fixes #253)

Author: sindrets

lua/diffview/bootstrap.lua

@@ -9,48 +9,6 @@ local function err(msg)
   vim.cmd("echohl NONE")
 end
 
-local function exists_in_runtime(module_name)
-  --#region From neovim/runtime/lua/vim/_init_packages.lua:
-  local basename = module_name:gsub('%.', '/')
-  local paths = { "lua/" .. basename .. ".lua", "lua/" .. basename .. "/init.lua" }
-
-  local found = vim.api.nvim__get_runtime(paths, false, { is_lua = true })
-  if found[1] then
-    return true
-  end
-
-  local so_paths = {}
-  for _, trail in ipairs(vim._so_trails) do
-    local path = "lua" .. trail:gsub('?', basename) -- so_trails contains a leading slash
-    table.insert(so_paths, path)
-  end
-
-  found = vim.api.nvim__get_runtime(so_paths, false, { is_lua = true })
-  if found[1] then
-    return true
-  end
-  --#endregion
-
-  return false
-end
-
-local function is_module_available(name)
-  if package.loaded[name] then
-    return true
-  end
-
-  ---@diagnostic disable-next-line: undefined-field
-  if _G.__luacache and _G.__luacache.print_profile then
-    -- WORKAROUND: If the user has impatient.nvim with profiling enabled: just
-    -- do a normal require.
-    -- @See [issue #144](https://github.com/sindrets/diffview.nvim/issues/144).
-    local ok, _ = pcall(require, name)
-    return ok
-  end
-
-  return exists_in_runtime(name)
-end
-
 _G.DiffviewGlobal = {
   bootstrap_done = true,
   bootstrap_ok = false,
@@ -64,15 +22,6 @@ if vim.fn.has("nvim-0.7") ~= 1 then
   return false
 end
 
--- Ensure dependencies
-if not is_module_available("plenary") then
-  err(
-    "Dependency 'plenary.nvim' is not installed! "
-    .. "See ':h diffview.changelog-93' for more information."
-  )
-  return false
-end
-
 _G.DiffviewGlobal = {
   ---Debug Levels:
   ---0:     NOTHING

lua/diffview/health.lua

@@ -0,0 +1,98 @@
+local health = vim.health or require("health")
+local config = require("diffview.config")
+
+local M = {}
+
+M.plugin_deps = {
+  {
+    name = "plenary",
+    optional = false,
+  },
+  {
+    name = "nvim-web-devicons",
+    optional = true,
+  },
+}
+
+---@param cmd string|string[]
+---@return string[] stdout
+---@return integer code
+local function system_list(cmd)
+  local out = vim.fn.systemlist(cmd)
+  return out or {}, vim.v.shell_error
+end
+
+local function lualib_available(name)
+  local ok, _ = pcall(require, name)
+  return ok
+end
+
+function M.check()
+  if vim.fn.has("nvim-0.7") == 0 then
+    health.report_error("Diffview.nvim requires Neovim 0.7.0+")
+  end
+
+  health.report_start("Checking plugin dependencies")
+
+  for _, plugin in ipairs(M.plugin_deps) do
+    if lualib_available(plugin.name) then
+      health.report_ok(plugin.name .. " installed.")
+    else
+      if plugin.optional then
+        health.report_warn(("Optional dependency '%s' not found."):format(plugin.name))
+      else
+        health.report_error(("Dependency '%s' not found!"):format(plugin.name))
+      end
+    end
+  end
+
+  health.report_start("Checking external dependencies")
+
+  -- Git
+  ;(function()
+    local conf = config.get_config()
+    local out, code = system_list(vim.tbl_flatten({ conf.git_cmd, "version" }))
+
+    if code ~= 0 or not out[1] then
+      health.report_error(
+        "Configured git command is not executable: " .. table.concat(conf.git_cmd, " "
+      ))
+      return
+    else
+      health.report_ok("Git found.")
+    end
+
+    local version_string = out[1]:match("git version (%S+)")
+
+    if not version_string then
+      health.report_error("Could not determine git version!")
+      return
+    end
+
+    local current = {}
+    local target = {
+      major = 2,
+      minor = 31,
+      patch = 0,
+    }
+    local target_version_string = ("%d.%d.%d"):format(target.major, target.minor, target.patch)
+    local parts = vim.split(version_string, "%.")
+    current.major = tonumber(parts[1])
+    current.minor = tonumber(parts[2])
+    current.patch = tonumber(parts[3]) or 0
+
+    local cs = ("%08d%08d%08d"):format(current.major, current.minor, current.patch)
+    local ts = ("%08d%08d%08d"):format(target.major, target.minor, target.patch)
+
+    if cs < ts then
+      health.report_error(("Git version is outdated! Wanted: %s, current: %s"):format(
+        target_version_string,
+        version_string
+      ))
+    else
+      health.report_ok("Git is up-to-date.")
+    end
+  end)()
+end
+
+return M