feat: add default condition for postfix

DOC.md

@@ -1652,8 +1652,7 @@ The optional third argument is the same as the third (`opts`) argument to the
 
 The postfix snippet works using a callback on the pre_expand event of the
 snippet. If you pass a callback on the pre_expand event (structure example
-below) it will get run after the builtin callback. This means that your
-callback will have access to the `POSTFIX_MATCH` field as well.
+below) it will get run after the builtin callback.
 
 ```lua
 {

doc/luasnip.txt

@@ -1,4 +1,4 @@
-*luasnip.txt*             For NVIM v0.8.0             Last change: 2023 May 25
+*luasnip.txt*             For NVIM v0.8.0             Last change: 2023 May 26
 
 ==============================================================================
 Table of Contents                                  *luasnip-table-of-contents*
@@ -1562,8 +1562,7 @@ The optional third argument is the same as the third (`opts`) argument to the
 
 The postfix snippet works using a callback on the pre_expand event of the
 snippet. If you pass a callback on the pre_expand event (structure example
-below) it will get run after the builtin callback. This means that your
-callback will have access to the `POSTFIX_MATCH` field as well.
+below) it will get run after the builtin callback.
 
 >lua
     {

lua/luasnip/extras/postfix.lua

@@ -55,6 +55,18 @@ local function generate_opts(match_pattern, user_callback)
 	}
 end
 
+local function wrap_condition(user_condition, match_pattern)
+	if not user_condition then
+		user_condition = require("luasnip.util.util").yes
+	end
+
+	return function(line_to_cursor, matched_trigger, captures)
+		return line_to_cursor:sub(1, -1 - #matched_trigger):match(match_pattern)
+				~= nil
+			and user_condition(line_to_cursor, matched_trigger, captures)
+	end
+end
+
 local function postfix(context, nodes, opts)
 	opts = opts or {}
 	local user_callback = vim.tbl_get(opts, "callbacks", -1, events.pre_expand)
@@ -65,17 +77,11 @@ local function postfix(context, nodes, opts)
 		user_callback = { user_callback, { "nil", "function" } },
 	})
 
-	local match_pattern
-	if type(context) == "string" then
-		context = {
-			trig = context,
-		}
-		match_pattern = matches.default
-	else
-		match_pattern = context.match_pattern or matches.default
-	end
+	context = node_util.wrap_context(context)
+	context.wordTrig = false
+	local match_pattern = context.match_pattern or matches.default
+	context.condition = wrap_condition(context.condition, match_pattern)
 
-	context = vim.tbl_deep_extend("keep", context, { wordTrig = false })
 	opts = vim.tbl_deep_extend(
 		"force",
 		opts,