Basic partial class support

changelog.md

@@ -13,6 +13,20 @@
   ```
 * `NEW` Test CLI: `--name=<testname>` `-n=<testname>`: run specify unit test
 * `FIX` Fixed the error that the configuration file pointed to by the `--configpath` option was not read and loaded.
+* `NEW` `---@class` supports attribute `partial`, which will not check missing inherited fields [#3023](https://github.com/LuaLS/lua-language-server/issues/3023)
+  ```lua
+  ---@class Config
+  ---@field a number
+
+  ---@class (partial) Config.P: Config
+  ---@field b number
+
+  ---@type Config.P[]
+  local cfgs = {}
+  cfgs[1] = { b = 1 } -- no warning
+  cfgs[2] = {}        -- only warns missing `b`
+  ```
+  This enables the previous missing field check behavior before [#2970](https://github.com/LuaLS/lua-language-server/issues/2970)
 
 ## 3.13.5
 `2024-12-20`

script/core/diagnostics/missing-fields.lua

@@ -26,6 +26,18 @@ return function (uri, callback)
                 local className = def.class[1]
                 if not sortedDefs[className] then
                     sortedDefs[className] = {}
+                    -- check if this class is a `partial` class
+                    -- a partial class will not check missing inherited fields
+                    local class = vm.getGlobal('type', className)
+                    ---@cast class -nil
+                    for _, set in ipairs(class:getSets(uri)) do
+                        if set.type == 'doc.class'
+                        and vm.docHasAttr(set, 'partial')
+                        then
+                            sortedDefs[className].isPartial = true
+                            break
+                        end
+                    end
                 end
                 local samedefs = sortedDefs[className]
                 samedefs[#samedefs+1] = def
@@ -41,8 +53,8 @@ return function (uri, callback)
         for className, samedefs in pairs(sortedDefs) do
             local missedKeys = {}
             for _, def in ipairs(samedefs) do
-                local fields = vm.getFields(def)
-                if #fields == 0 then
+                local fields = samedefs.isPartial and def.fields or vm.getFields(def)
+                if not fields or #fields == 0 then
                     goto continue
                 end
 
@@ -78,6 +90,12 @@ return function (uri, callback)
                     end
                 end
                 ::continue::
+
+                if not samedefs.isPartial then
+                    -- if not partial class, then all fields in this class have already been checked
+                    -- because in the above uses `vm.getFields` to get all fields
+                    break
+                end
             end
 
             if #missedKeys == 0 then

test/diagnostics/missing-fields.lua

@@ -462,4 +462,38 @@ local function f(b) end
 f <!{y = 1}!>
 ]]
 
+-- partial class
+
+TEST[[
+---@class A
+---@field x number
+
+---@class (partial) B: A
+
+---@type B
+local t = {}
+]]
+
+TEST[[
+---@class A
+---@field x number
+
+---@class (partial) B: A
+---@field y number
+
+---@type B
+local t = <!{}!>
+]]
+
+TEST[[
+---@class A
+---@field x number
+
+---@class (partial) B: A
+---@field y number
+
+---@type B
+local t = {y = 1}
+]]
+
 --