From 1f2ce329848d59c31913b18c869d0ecc66c8ced2 Mon Sep 17 00:00:00 2001
From: Tom Lau <tomandfatboy@gmail.com>
Date: Sun, 13 Oct 2024 15:13:39 +0800
Subject: [PATCH] fix: regression related to type narrow and generic since
 v3.10.1

---
 changelog.md                   |  1 +
 script/vm/compiler.lua         |  8 +++++---
 test/type_inference/common.lua | 20 ++++++++++++++++++++
 3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/changelog.md b/changelog.md
index 2acd8ab7e..aadfbade9 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` A regression related to type narrow and generic param introduced since `v3.10.1`
 
 ## 3.11.1
 `2024-10-9`
diff --git a/script/vm/compiler.lua b/script/vm/compiler.lua
index aa51bcddf..8701e8d7b 100644
--- a/script/vm/compiler.lua
+++ b/script/vm/compiler.lua
@@ -630,15 +630,17 @@ local function matchCall(source)
         newNode.originNode = myNode
         vm.setNode(source, newNode, true)
         if call.args then
-            -- clear node caches of args to allow recomputation with the type narrowed call
+            -- clear existing node caches of args to allow recomputation with the type narrowed call
             for _, arg in ipairs(call.args) do
-                vm.setNode(arg, vm.createNode(), true)
+                if vm.getNode(arg) then
+                    vm.setNode(arg, vm.createNode(), true)
+                end
             end
             for n in newNode:eachObject() do
                 if n.type == 'function'
                 or n.type == 'doc.type.function' then
                     for i, arg in ipairs(call.args) do
-                        if n.args[i] then
+                        if vm.getNode(arg) and n.args[i] then
                             vm.setNode(arg, vm.compileNode(n.args[i]))
                         end
                     end
diff --git a/test/type_inference/common.lua b/test/type_inference/common.lua
index 792967722..89ba92f6f 100644
--- a/test/type_inference/common.lua
+++ b/test/type_inference/common.lua
@@ -4571,3 +4571,23 @@ else
     local <?b?> = a
 end
 ]]
+
+TEST 'nil' [[
+---@generic T
+---@param v T
+---@return T
+---@overload fun(): nil
+local function f(v) end
+
+local <?r?> = f()
+]]
+
+TEST 'string' [[
+---@generic T
+---@param v T
+---@return T
+---@overload fun(): nil
+local function f(v) end
+
+local <?r?> = f('')
+]]