infer `nil` as redundant return value

5 files changed, 34 insertions, 2 deletions

diff --git a/changelog.md b/changelog.md
index 2048c043..2b9f5b00 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,12 @@
 # changelog
 
+## 3.4.0
+* `CHG` infer `nil` as redundant return value
+  ```lua
+  local function f() end
+  local x = f() -- `x` is `nil` instead of `unknown`
+  ```
+
 ## 3.3.1
 * `FIX` [#1213](https://github.com/sumneko/lua-language-server/issues/1213)
 * `FIX` [#1215](https://github.com/sumneko/lua-language-server/issues/1215)
diff --git a/script/vm/compiler.lua b/script/vm/compiler.lua
index 29de39ae..65df3a1d 100644
--- a/script/vm/compiler.lua
+++ b/script/vm/compiler.lua
@@ -667,7 +667,7 @@ local function selectNode(source, list, index)
             if list[i] then
                 local last = list[i]
                 if last.type == 'call'
-                or last.type == '...' then
+                or last.type == 'varargs' then
                     index = index - i + 1
                     exp = last
                 end
@@ -1376,9 +1376,11 @@ local compilerSwitch = util.switch()
         local hasMarkDoc
         if func.bindDocs then
             local sign = getObjectSign(func)
+            local lastReturn
             for _, doc in ipairs(func.bindDocs) do
                 if doc.type == 'doc.return' then
                     for _, rtn in ipairs(doc.returns) do
+                        lastReturn = rtn
                         if rtn.returnIndex == index then
                             hasMarkDoc = true
                             local hasGeneric
@@ -1396,12 +1398,18 @@ local compilerSwitch = util.switch()
                     end
                 end
             end
+            if lastReturn and not hasMarkDoc and lastReturn.types[1][1] == '...' then
+                vm.setNode(source, vm.getGlobal('type', 'unknown'))
+            end
         end
         if func.returns and not hasMarkDoc then
             for _, rtn in ipairs(func.returns) do
                 selectNode(source, rtn, index)
             end
         end
+        if vm.getNode(source):isEmpty() then
+            vm.setNode(source, vm.getGlobal('type', 'nil'))
+        end
     end)
     : case 'main'
     : call(function (source)
diff --git a/script/vm/type.lua b/script/vm/type.lua
index 8027e933..3eb42e51 100644
--- a/script/vm/type.lua
+++ b/script/vm/type.lua
@@ -39,7 +39,8 @@ function vm.isSubNode(child, parent, mark)
     mark = mark or {}
     local childName  = getNodeName(child)
     local parentName = getNodeName(parent)
-    if childName == 'any' or parentName == 'any' then
+    if childName == 'any'
+    or parentName == 'any' then
         return true
     end
 
diff --git a/test/diagnostics/common.lua b/test/diagnostics/common.lua
index d9dfb0b9..d7ec4b63 100644
--- a/test/diagnostics/common.lua
+++ b/test/diagnostics/common.lua
@@ -1608,3 +1608,12 @@ local x = 0
 
 <!x!> = true
 ]]
+
+TEST [[
+---@diagnostic disable: unused-local
+
+---@type integer
+local x
+
+<!x!> = true
+]]
diff --git a/test/type_inference/init.lua b/test/type_inference/init.lua
index 32a35fbd..c402cb8d 100644
--- a/test/type_inference/init.lua
+++ b/test/type_inference/init.lua
@@ -2650,3 +2650,10 @@ x = call(x)
 
 print(<?x?>)
 ]]
+
+TEST 'nil' [[
+local function f()
+end
+
+local <?x?> = f()
+]]