feat: syntax for using first available formatter

Alternations are now supported. You can specify a sub-list in place of a
formatter name and conform will use the first formatter in that list
that is available. For example, this will use either prettierd or
prettier (whichever is available), and then always trim whitespace
afterwards:

conform.format(formatters = { { "prettierd", "prettier" }, "trim_whitespace" })

This syntax is available both in the formatters_by_ft config option and
in the `formatters` argument of the `format` method.

1 files changed, 65 insertions, 27 deletions

diff --git a/lua/conform/health.lua b/lua/conform/health.lua
index d36ef03..18085bf 100644
--- a/lua/conform/health.lua
+++ b/lua/conform/health.lua
@@ -6,11 +6,24 @@ local function get_formatter_filetypes(name)
   local conform = require("conform")
   local filetypes = {}
   for filetype, formatters in pairs(conform.formatters_by_ft) do
+    -- support the old structure where formatters could be a subkey
     if not vim.tbl_islist(formatters) then
+      ---@diagnostic disable-next-line: undefined-field
       formatters = formatters.formatters
     end
-    if vim.tbl_contains(formatters, name) then
-      table.insert(filetypes, filetype)
+
+    for _, ft_name in ipairs(formatters) do
+      if type(ft_name) == "string" then
+        if ft_name == name then
+          table.insert(filetypes, filetype)
+          break
+        end
+      else
+        if vim.tbl_contains(ft_name, name) then
+          table.insert(filetypes, filetype)
+          break
+        end
+      end
     end
   end
   return filetypes
@@ -38,6 +51,22 @@ M.check = function()
   end
 end
 
+---@param formatters conform.FormatterUnit[]
+---@return string[]
+local function flatten_formatters(formatters)
+  local flat = {}
+  for _, name in ipairs(formatters) do
+    if type(name) == "string" then
+      table.insert(flat, name)
+    else
+      for _, f in ipairs(flatten_formatters(name)) do
+        table.insert(flat, f)
+      end
+    end
+  end
+  return flat
+end
+
 M.show_window = function()
   local conform = require("conform")
   local lines = {}
@@ -60,35 +89,43 @@ M.show_window = function()
   end
   table.insert(lines, "")
 
-  ---@param formatters conform.FormatterInfo[]
+  ---@param formatter conform.FormatterInfo
+  local function append_formatter_info(formatter)
+    if not formatter.available then
+      local line = string.format("%s unavailable: %s", formatter.name, formatter.available_msg)
+      table.insert(lines, line)
+      table.insert(
+        highlights,
+        { "DiagnosticWarn", #lines, formatter.name:len(), formatter.name:len() + 12 }
+      )
+    else
+      local filetypes = get_formatter_filetypes(formatter.name)
+      local line = string.format("%s ready (%s)", formatter.name, table.concat(filetypes, ", "))
+      table.insert(lines, line)
+      table.insert(
+        highlights,
+        { "DiagnosticInfo", #lines, formatter.name:len(), formatter.name:len() + 6 }
+      )
+    end
+  end
+
+  local seen = {}
+  ---@param formatters string[]
   local function append_formatters(formatters)
-    for _, formatter in ipairs(formatters) do
-      if not formatter.available then
-        local line = string.format("%s unavailable: %s", formatter.name, formatter.available_msg)
-        table.insert(lines, line)
-        table.insert(
-          highlights,
-          { "DiagnosticWarn", #lines, formatter.name:len(), formatter.name:len() + 12 }
-        )
+    for _, name in ipairs(formatters) do
+      if type(name) == "table" then
+        append_formatters(name)
       else
-        local filetypes = get_formatter_filetypes(formatter.name)
-        local line = string.format("%s ready (%s)", formatter.name, table.concat(filetypes, ", "))
-        table.insert(lines, line)
-        table.insert(
-          highlights,
-          { "DiagnosticInfo", #lines, formatter.name:len(), formatter.name:len() + 6 }
-        )
+        seen[name] = true
+        local formatter = conform.get_formatter_info(name)
+        append_formatter_info(formatter)
       end
     end
   end
 
   table.insert(lines, "Formatters for this buffer:")
   table.insert(highlights, { "Title", #lines, 0, -1 })
-  local seen = {}
-  local buf_formatters = conform.list_formatters_for_buffer()
-  for _, formatter in ipairs(buf_formatters) do
-    seen[formatter.name] = true
-  end
+  local buf_formatters = flatten_formatters(conform.list_formatters_for_buffer())
   append_formatters(buf_formatters)
   if vim.tbl_isempty(buf_formatters) then
     table.insert(lines, "<none>")
@@ -97,10 +134,11 @@ M.show_window = function()
   table.insert(lines, "")
   table.insert(lines, "Other formatters:")
   table.insert(highlights, { "Title", #lines, 0, -1 })
-  local all_formatters = vim.tbl_filter(function(f)
-    return not seen[f.name]
-  end, conform.list_all_formatters())
-  append_formatters(all_formatters)
+  for _, formatter in ipairs(conform.list_all_formatters()) do
+    if not seen[formatter.name] then
+      append_formatter_info(formatter)
+    end
+  end
 
   local bufnr = vim.api.nvim_create_buf(false, true)
   local winid = vim.api.nvim_open_win(bufnr, true, {