fix: regression related to type narrow and generic since v3.10.1

Author: tomlau10

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`

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

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('')
+]]