resolve #1105 infer type by `type(x)`

4 files changed, 106 insertions, 20 deletions

diff --git a/changelog.md b/changelog.md
index 01cb797f..15042aa8 100644
--- a/changelog.md
+++ b/changelog.md
@@ -26,6 +26,14 @@
 
   local s = t and t.x or 1 -- `t` in `t.x` is `table`
   ```
+* `CHG` infer type by `type(x)`
+  ```lua
+  local x
+
+  if type(x) == 'string' then
+    print(x) -- `x` is `string` here
+  end
+  ```
 * `FIX` with clients that support LSP 3.17 (VSCode), workspace diagnostics are triggered every time when opening a file.
 * `FIX` [#1204](https://github.com/sumneko/lua-language-server/issues/1204)
 * `FIX` [#1208](https://github.com/sumneko/lua-language-server/issues/1208)
diff --git a/script/vm/node.lua b/script/vm/node.lua
index 5086f66d..1b3ea45c 100644
--- a/script/vm/node.lua
+++ b/script/vm/node.lua
@@ -224,6 +224,32 @@ function mt:remove(name)
     return self
 end
 
+---@param name string
+function mt:narrow(name)
+    if name ~= 'nil' and self.optional == true then
+        self.optional = nil
+    end
+    for index = #self, 1, -1 do
+        local c = self[index]
+        if (c.type == 'global' and c.cate == 'type' and c.name == name)
+        or (c.type == name)
+        or (c.type == 'doc.type.integer'  and (name == 'number' or name == 'integer'))
+        or (c.type == 'doc.type.boolean'  and name == 'boolean')
+        or (c.type == 'doc.type.table'    and name == 'table')
+        or (c.type == 'doc.type.array'    and name == 'table')
+        or (c.type == 'doc.type.function' and name == 'function') then
+            goto CONTINUE
+        end
+        table.remove(self, index)
+        self[c] = nil
+        ::CONTINUE::
+    end
+    if #self == 0 then
+        self[#self+1] = vm.getGlobal('type', name)
+    end
+    return self
+end
+
 ---@param node vm.node
 function mt:removeNode(node)
     for _, c in ipairs(node) do
diff --git a/script/vm/runner.lua b/script/vm/runner.lua
index 2e362871..e6f34656 100644
--- a/script/vm/runner.lua
+++ b/script/vm/runner.lua
@@ -208,30 +208,48 @@ function mt:_lookInto(action, topNode, outNode)
             outNode = outNode2
         elseif action.op.type == '=='
         or     action.op.type == '~=' then
-            local loc, checker
+            local exp, checker
             for i = 1, 2 do
-                if action[i].type == 'getlocal' and action[i].node == self._loc then
-                    loc = action[i]
-                    checker = action[3-i] -- Copilot tells me use `3-i` instead of `i%2+1`
-                elseif action[2].type == 'getlocal' and action[2].node == self._loc then
-                    loc = action[3-i]
+                if guide.isLiteral(action[i]) then
                     checker = action[i]
+                    exp     = action[3-i] -- Copilot tells me use `3-i` instead of `i%2+1`
                 end
             end
-            if loc then
-                self:_fastWard(loc.finish, topNode:copy())
-                if guide.isLiteral(checker) then
-                    local checkerNode = vm.compileNode(checker)
-                    if action.op.type == '==' then
-                        topNode = checkerNode
-                        if outNode then
-                            outNode:removeNode(topNode)
-                        end
-                    else
-                        topNode:removeNode(checkerNode)
-                        if outNode then
-                            outNode = checkerNode
-                        end
+            if not exp then
+                goto RETURN
+            end
+            if  exp.type == 'getlocal'
+            and exp.node == self._loc then
+                self:_fastWard(exp.finish, topNode:copy())
+                local checkerNode = vm.compileNode(checker)
+                if action.op.type == '==' then
+                    topNode = checkerNode
+                    if outNode then
+                        outNode:removeNode(topNode)
+                    end
+                else
+                    topNode:removeNode(checkerNode)
+                    if outNode then
+                        outNode = checkerNode
+                    end
+                end
+            elseif exp.type == 'call'
+            and    checker.type == 'string'
+            and    exp.node.special == 'type'
+            and    exp.args
+            and    exp.args[1]
+            and    exp.args[1].type == 'getlocal'
+            and    exp.args[1].node == self._loc then
+                self:_fastWard(exp.finish, topNode:copy())
+                if action.op.type == '==' then
+                    topNode:narrow(checker[1])
+                    if outNode then
+                        outNode:remove(checker[1])
+                    end
+                else
+                    topNode:remove(checker[1])
+                    if outNode then
+                        outNode:narrow(checker[1])
                     end
                 end
             end
diff --git a/test/type_inference/init.lua b/test/type_inference/init.lua
index a12e702f..20d2c6e9 100644
--- a/test/type_inference/init.lua
+++ b/test/type_inference/init.lua
@@ -2580,3 +2580,37 @@ local n
 
 n = ff[n and <?n?>.x]
 ]]
+
+TEST 'integer' [[
+local x
+
+if type(x) == 'integer' then
+    print(<?x?>)
+end
+]]
+
+TEST 'boolean|integer' [[
+local x
+
+if type(x) == 'integer'
+or type(x) == 'boolean' then
+    print(<?x?>)
+end
+]]
+
+TEST 'fun()' [[
+---@type fun()?
+local x
+
+if type(x) == 'function' then
+    print(<?x?>)
+end
+]]
+
+TEST 'function' [[
+local x
+
+if type(x) == 'function' then
+    print(<?x?>)
+end
+]]