fix: do not treat LuaDoc string "async" as async fun prefix

Author: cpruijsen

changelog.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 <!-- Add all new changes here. They will be moved under a version at release -->
+* `FIX` Literal string `"async"` in LuaDoc types (e.g. `---@field mode "async" | "sync"`) is no longer mis-parsed as the `async fun` prefix [#3402](https://github.com/LuaLS/lua-language-server/issues/3402)
 * `FIX` A `.gitignore` line containing only whitespace no longer ignores the entire workspace [#3458](https://github.com/LuaLS/lua-language-server/issues/3458)
 * `FIX` `need-check-nil` diagnostic is no longer reported on safe navigation access (e.g. `x?.field`, `f?.()`, `t?.[key]`), since the optional access itself already handles the nil check. Note that a non-safe access chained after a safe one (e.g. `x.upper()?.field`) still reports, because the safe access only protects its own result.
 

script/parser/luadoc.lua

@@ -669,7 +669,7 @@ end
 
 local function parseFunction(parent)
     local _, content = peekToken()
-    if content == 'async' then
+    if checkToken('name', 'async', 1) then
         nextToken()
         local pos = getStart()
         local tp, cont = peekToken()

test/parser_test/ast/LuaDoc.lua

@@ -405,6 +405,58 @@ LuaDoc [[
     },
 }
 
+LuaDoc [[
+---@field mode "async" | "sync"
+]]
+{
+    type   = "doc",
+    start  = 0,
+    finish = 10000,
+    parent = "<IGNORE>",
+    [1]    = {
+        type            = "doc.field",
+        start           = 10,
+        finish          = 31,
+        range           = 31,
+        parent          = "<IGNORE>",
+        field           = {
+            type   = "doc.field.name",
+            start  = 10,
+            finish = 14,
+            parent = "<IGNORE>",
+            [1]    = "mode",
+        },
+        bindComments    = {
+        },
+        extends         = {
+            type        = "doc.type",
+            start       = 15,
+            finish      = 31,
+            parent      = "<IGNORE>",
+            firstFinish = 31,
+            types       = {
+                [1] = {
+                    type   = "doc.type.string",
+                    start  = 15,
+                    finish = 22,
+                    parent = "<IGNORE>",
+                    [1]    = "async",
+                    [2]    = "\"",
+                },
+                [2] = {
+                    type   = "doc.type.string",
+                    start  = 25,
+                    finish = 31,
+                    parent = "<IGNORE>",
+                    [1]    = "sync",
+                    [2]    = "\"",
+                },
+            },
+        },
+        originalComment = "<IGNORE>",
+    },
+}
+
 LuaDoc [[
 ---@field private open function|string
 ]]