fix: type narrowing bugs with literal fields

changelog.md

@@ -8,6 +8,7 @@
 * `FIX` reimplement section `luals.config` in file doc.json
 * `FIX` incorrect file names in file doc.json
 * `FIX` remove extra `./` path prefix in the check report when using `--check=.`
+* `FIX` Narrowing of types with literal fields: [#3056](https://github.com/LuaLS/lua-language-server/issues/3056), [#3089](https://github.com/LuaLS/lua-language-server/issues/3089)
 
 ## 3.13.6
 `2025-2-6`

script/vm/tracer.lua

@@ -268,6 +268,11 @@ local function getNodeTypesWithLiteralField(uri, source, fieldName, literal)
         return
     end
 
+    -- Literal must has a value
+    if literal[1] == nil then
+        return
+    end
+
     local tys
 
     for _, c in ipairs(vm.compileNode(loc)) do
@@ -277,10 +282,10 @@ local function getNodeTypesWithLiteralField(uri, source, fieldName, literal)
                     for _, f in ipairs(set.fields) do
                         if f.field[1] == fieldName then
                             for _, t in ipairs(f.extends.types) do
-                                if t[1] == literal[1] then
-                                  tys = tys or {}
-                                  table.insert(tys, {set.class[1], #f.extends.types > 1})
-                                  break
+                                if guide.isLiteral(t) and t[1] ~= nil and t[1] == literal[1] then
+                                    tys = tys or {}
+                                    table.insert(tys, { set.class[1], #f.extends.types > 1 })
+                                    break
                                 end
                             end
                             break

test/diagnostics/need-check-nil.lua

@@ -66,3 +66,17 @@ end
 
 x()
 ]]
+
+-- #3056
+TEST [[
+---@class A
+---@field b string
+---@field c 'string'|string1'
+---@field d 0|1|2
+
+---@type A?
+local a
+
+if <!a!>.b == "string1" then end
+if <!a!>.b == "string" then end
+]]

test/type_inference/common.lua

@@ -4606,6 +4606,31 @@ local a = {}
 function a:func(<?x?>) end
 ]]
 
+-- #3089
+TEST 'fun(x: number, y: number)' [[
+---@class Person
+---@field age? number
+---@field foo fun(x: number, y: number)
+
+---@param person Person
+local function test(person)
+    if person.foo ~= nil then
+        local <?b?> = person.foo
+    end
+end
+]]
+
+-- #2952
+TEST 'A' [[
+---@class A
+---@field b {[C]:D}
+local A
+
+if A.b ~= {} then
+    local C = <?A?>
+end
+]]
+
 TEST 'A' [[
 ---@class A
 ---@field type 'a'