From 7fa9e424b08f8d037a9c289c692caa87f26d6b3e Mon Sep 17 00:00:00 2001
From: Christopher Pruijsen <christopher.pruijsen@gmail.com>
Date: Tue, 29 Sep 2026 04:10:06 +0100
Subject: [PATCH] fix: LuaJIT ?? strips optional ? from the left-hand type

integer? stores nil as a node flag, so ?? never saw a nil object and
copied the optional type unchanged. Treat isOptional() as hasNil so
the existing removeOptional() branch runs.
---
 changelog.md                   | 1 +
 script/vm/operator.lua         | 2 +-
 test/type_inference/common.lua | 8 ++++++++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/changelog.md b/changelog.md
index f712d4813..b9916c8e9 100644
--- a/changelog.md
+++ b/changelog.md
@@ -2,6 +2,7 @@
 
 ## Unreleased
 <!-- Add all new changes here. They will be moved under a version at release -->
+* `FIX` LuaJIT nil-coalescing `??` now strips the optional `?` from the left-hand type (e.g. `integer? ?? 2` infers `integer`) [#3459](https://github.com/LuaLS/lua-language-server/issues/3459)
 * `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.
 
diff --git a/script/vm/operator.lua b/script/vm/operator.lua
index bb71b02b2..ed53cdfc3 100644
--- a/script/vm/operator.lua
+++ b/script/vm/operator.lua
@@ -272,7 +272,7 @@ vm.binarySwitch = util.switch()
         local node2 = vm.compileNode(source[2])
         -- 统计具体类型：variable/local 是引用元信息，无具体类型时视为未知（可能为 nil）
         local count   = 0
-        local hasNil  = false
+        local hasNil  = node1:isOptional()
         for c in node1:eachObject() do
             if c.type == 'nil'
             or (c.type == 'global' and c.cate == 'type' and c.name == 'nil') then
diff --git a/test/type_inference/common.lua b/test/type_inference/common.lua
index 775634028..9a9d74355 100644
--- a/test/type_inference/common.lua
+++ b/test/type_inference/common.lua
@@ -3312,6 +3312,14 @@ end
 local <?x?> = n or 0
 ]]
 
+config.set(nil, 'Lua.runtime.nonstandardSymbol', { '??' })
+TEST 'integer' [[
+---@type integer?
+local foo = 1
+local <?bar?> = foo ?? 2
+]]
+config.set(nil, 'Lua.runtime.nonstandardSymbol', {})
+
 TEST 'number' [=[
 local <?x?> = F()--[[@as number]]
 ]=]