resolve #1280

Author: sumneko

changelog.md

@@ -3,6 +3,14 @@
 ## 3.4.1
 * `NEW` settings:
   * `type.weakNilCheck`
+* `CHG` allow type contravariance for `setmetatable` when initializing a class
+  ```lua
+  ---@class A
+  local a = {}
+
+  ---@class B: A
+  local b = setmetatable({}, { __index = a }) -- OK!
+  ```
 * `FIX` [#1256](https://github.com/sumneko/lua-language-server/issues/1256)
 * `FIX` [#1257](https://github.com/sumneko/lua-language-server/issues/1257)
 * `FIX` [#1267](https://github.com/sumneko/lua-language-server/issues/1267)

script/core/diagnostics/assign-type-mismatch.lua

@@ -30,6 +30,20 @@ local function hasMarkType(source)
     return false
 end
 
+---@param source parser.object
+---@return boolean
+local function hasMarkClass(source)
+    if not source.bindDocs then
+        return false
+    end
+    for _, doc in ipairs(source.bindDocs) do
+        if doc.type == 'doc.class' then
+            return true
+        end
+    end
+    return false
+end
+
 ---@async
 return function (uri, callback)
     local state = files.getState(uri)
@@ -72,6 +86,18 @@ return function (uri, callback)
         if vm.canCastType(uri, varNode, valueNode) then
             return
         end
+
+        if  value.type == 'select'
+        and value.sindex == 1
+        and value.vararg
+        and value.vararg.type == 'call'
+        and value.vararg.node.special == 'setmetatable'
+        and hasMarkClass(source) then
+            if vm.canCastType(uri, valueNode:copy():remove 'table', varNode) then
+                return
+            end
+        end
+
         callback {
             start   = source.start,
             finish  = source.finish,

script/vm/node.lua

@@ -227,7 +227,7 @@ function mt:remove(name)
         or (c.type == 'doc.type.boolean'  and name == 'false' and c[1] == false)
         or (c.type == 'doc.type.table'    and name == 'table')
         or (c.type == 'doc.type.array'    and name == 'table')
-        or (c.type == 'doc.type.sign'    and name == 'table')
+        or (c.type == 'doc.type.sign'     and name == 'table')
         or (c.type == 'doc.type.function' and name == 'function') then
             table.remove(self, index)
             self[c] = nil

test/diagnostics/type-check.lua

@@ -631,5 +631,38 @@ n = nb
 ]]
 config.set(nil, 'Lua.type.weakNilCheck', false)
 
+TEST [[
+---@class A
+local a = {}
+
+---@class B: A
+local <!b!> = a
+]]
+
+TEST [[
+---@class A
+local a = {}
+a.__index = a
+
+---@class B: A
+local b = setmetatable({}, a)
+]]
+
+TEST [[
+---@class A
+local a = {}
+
+---@class B: A
+local b = setmetatable({}, {__index = a})
+]]
+
+TEST [[
+---@class A
+local a = {}
+
+---@class B
+local <!b!> = setmetatable({}, {__index = a})
+]]
+
 config.remove(nil, 'Lua.diagnostics.disable', 'unused-local')
 config.remove(nil, 'Lua.diagnostics.disable', 'undefined-global')