Fix incorrect function params' type infer when there is only @overload

changelog.md

@@ -8,6 +8,7 @@
 * `FIX` Fix `VM.OnCompileFunctionParam` function in plugins
 * `FIX` Lua 5.1: fix incorrect warning when using setfenv with an int as first parameter
 * `FIX` Improve type narrow by checking exact match on literal type params
+* `FIX` Incorrect function params' type infer when there is only `@overload` [#2509](https://github.com/LuaLS/lua-language-server/issues/2509) [#2708](https://github.com/LuaLS/lua-language-server/issues/2708) [#2709](https://github.com/LuaLS/lua-language-server/issues/2709)
 
 ## 3.10.5
 `2024-8-19`

script/vm/compiler.lua

@@ -1099,6 +1099,7 @@ local function compileFunctionParam(func, source)
 
     -- local call ---@type fun(f: fun(x: number));call(function (x) end) --> x -> number
     local funcNode = vm.compileNode(func)
+    local found = false
     for n in funcNode:eachObject() do
         if n.type == 'doc.type.function' and n.args[aindex] then
             local argNode = vm.compileNode(n.args[aindex])
@@ -1107,9 +1108,16 @@ local function compileFunctionParam(func, source)
                     vm.setNode(source, an)
                 end
             end
-            return true
+            -- NOTE: keep existing behavior for local call which only set type based on the 1st match
+            if func.parent.type == 'callargs' then
+                return true
+            end
+            found = true
         end
     end
+    if found then
+        return true
+    end
 
     local derviationParam = config.get(guide.getUri(func), 'Lua.type.inferParamType')
     if derviationParam and func.parent.type == 'local' and func.parent.ref then

script/vm/function.lua

@@ -359,6 +359,7 @@ end
 ---@return number
 local function calcFunctionMatchScore(uri, args, func)
     if vm.isVarargFunctionWithOverloads(func)
+    or vm.isFunctionWithOnlyOverloads(func)
     or not isAllParamMatched(uri, args, func.args)
     then
         return -1
@@ -490,6 +491,36 @@ function vm.isVarargFunctionWithOverloads(func)
     return false
 end
 
+---@param func table
+---@return boolean
+function vm.isFunctionWithOnlyOverloads(func)
+    if func.type ~= 'function' then
+        return false
+    end
+    if func._onlyOverloadFunction ~= nil then
+        return func._onlyOverloadFunction
+    end
+
+    if not func.bindDocs then
+        func._onlyOverloadFunction = false
+        return false
+    end
+    local hasOverload = false
+    for _, doc in ipairs(func.bindDocs) do
+        if doc.type == 'doc.overload' then
+            hasOverload = true
+        elseif doc.type == 'doc.param'
+        or doc.type == 'doc.return'
+        then
+            -- has specified @param or @return, thus not only @overload
+            func._onlyOverloadFunction = false
+            return false
+        end
+    end
+    func._onlyOverloadFunction = hasOverload
+    return true
+end
+
 ---@param func parser.object
 ---@return boolean
 function vm.isEmptyFunction(func)

test/type_inference/param_match.lua

@@ -172,6 +172,44 @@ local v = 'y'
 local <?r?> = f(v)
 ]]
 
+TEST 'string|number' [[
+---@overload fun(a: string)
+---@overload fun(a: number)
+local function f(<?a?>) end
+]]
+
+TEST '1|2' [[
+---@overload fun(a: 1)
+---@overload fun(a: 2)
+local function f(<?a?>) end
+]]
+
+TEST 'string' [[
+---@overload fun(a: 1): string
+---@overload fun(a: 2): number
+local function f(a) end
+
+local <?r?> = f(1)
+]]
+
+TEST 'number' [[
+---@overload fun(a: 1): string
+---@overload fun(a: 2): number
+local function f(a) end
+
+local <?r?> = f(2)
+]]
+
+TEST 'string|number' [[
+---@overload fun(a: 1): string
+---@overload fun(a: 2): number
+local function f(a) end
+
+---@type number
+local v
+local <?r?> = f(v)
+]]
+
 TEST 'number' [[
 ---@overload fun(a: 1, c: fun(x: number))
 ---@overload fun(a: 2, c: fun(x: string))