infer by if not x then return end

Author: sumneko

.luarc.json

@@ -10,6 +10,7 @@
             "discard-returns": "Any",
             "redundant-parameter": "Any",
             "missing-parameter": "Any",
+            "need-check-nil": "Any",
             "redundant-value": "Any",
             "deprecated": "Any"
         },

script/parser/newparser.lua

@@ -2947,13 +2947,25 @@ local function parseReturn()
     end
     pushActionIntoCurrentChunk(rtn)
     for i = #Chunk, 1, -1 do
-        local func = Chunk[i]
-        if func.type == 'function'
-        or func.type == 'main' then
-            if not func.returns then
-                func.returns = {}
+        local block = Chunk[i]
+        if block.type == 'function'
+        or block.type == 'main' then
+            if not block.returns then
+                block.returns = {}
             end
-            func.returns[#func.returns+1] = rtn
+            block.returns[#block.returns+1] = rtn
+            break
+        end
+    end
+    for i = #Chunk, 1, -1 do
+        local block = Chunk[i]
+        if block.type == 'ifblock'
+        or block.type == 'elseifblock'
+        or block.type == 'else' then
+            if not block.returns then
+                block.returns = {}
+            end
+            block.returns[#block.returns+1] = rtn
             break
         end
     end

script/vm/runner.lua

@@ -180,19 +180,28 @@ function mt:_compileBlock(block)
                     order = 3,
                 }
                 self:_compileNarrowByFilter(childBlock.filter, childBlock[1].start - 1)
-                local finalState = {
-                    type  = 'save',
-                    pos   = childBlock.finish,
-                    order = 1,
-                }
-                finals[#finals+1] = finalState
-                self.steps[#self.steps+1] = finalState
-                self.steps[#self.steps+1] = {
-                    type   = 'load',
-                    ref1   = outState,
-                    pos    = childBlock.finish,
-                    order  = 2,
-                }
+                if childBlock.returns then
+                    self.steps[#self.steps+1] = {
+                        type   = 'load',
+                        ref1   = outState,
+                        pos    = childBlock.finish,
+                        order  = 1,
+                    }
+                else
+                    local finalState = {
+                        type  = 'save',
+                        pos   = childBlock.finish,
+                        order = 1,
+                    }
+                    finals[#finals+1] = finalState
+                    self.steps[#self.steps+1] = finalState
+                    self.steps[#self.steps+1] = {
+                        type   = 'load',
+                        ref1   = outState,
+                        pos    = childBlock.finish,
+                        order  = 2,
+                    }
+                end
             end
         end
         for i, final in ipairs(finals) do

test/type_inference/init.lua

@@ -1840,6 +1840,17 @@ local x
 <?x?> = x or 1
 ]]
 
+TEST 'integer' [[
+---@type integer?
+local x
+
+if not x then
+    return
+end
+
+print(<?x?>)
+]]
+
 TEST 'integer' [=[
 local x