Add signature restriction for __spreadArray

Author: rbuckton

src/compiler/checker.ts

@@ -40726,6 +40726,11 @@ namespace ts {
                                         error(location, Diagnostics.This_syntax_requires_an_imported_helper_named_1_with_2_parameters_which_is_not_compatible_with_the_one_in_0_Consider_upgrading_your_version_of_0, externalHelpersModuleNameText, name, 5);
                                     }
                                 }
+                                else if (helper & ExternalEmitHelpers.SpreadArray) {
+                                    if (!some(getSignaturesOfSymbol(symbol), signature => getParameterCount(signature) > 2)) {
+                                        error(location, Diagnostics.This_syntax_requires_an_imported_helper_named_1_with_2_parameters_which_is_not_compatible_with_the_one_in_0_Consider_upgrading_your_version_of_0, externalHelpersModuleNameText, name, 3);
+                                    }
+                                }
                             }
                         }
                     }

tests/baselines/reference/arraySpreadImportHelpers.errors.txt

@@ -0,0 +1,16 @@
+tests/cases/conformance/es6/spread/main.ts(3,15): error TS2807: This syntax requires an imported helper named '__spreadArray' with 3 parameters, which is not compatible with the one in 'tslib'. Consider upgrading your version of 'tslib'.
+
+
+==== tests/cases/conformance/es6/spread/main.ts (1 errors) ====
+    export {};
+    const k = [1, , 2];
+    const o = [3, ...k, 4];
+                  ~~~~
+!!! error TS2807: This syntax requires an imported helper named '__spreadArray' with 3 parameters, which is not compatible with the one in 'tslib'. Consider upgrading your version of 'tslib'.
+    
+==== tests/cases/conformance/es6/spread/tslib.d.ts (0 errors) ====
+    // this is a pre-TS4.4 versions of emit helper, which always forced array packing
+    declare module "tslib" {
+        function __spreadArray(to: any[], from: any[]): any[];
+    }
+    

tests/cases/conformance/es6/spread/arraySpreadImportHelpers.ts

@@ -0,0 +1,16 @@
+// @target: es5
+// @importHelpers: true
+// @isolatedModules: true
+// @noTypesAndSymbols: true
+// @noEmit: true
+// @filename: main.ts
+
+export {};
+const k = [1, , 2];
+const o = [3, ...k, 4];
+
+// @filename: tslib.d.ts
+// this is a pre-TS4.4 versions of emit helper, which always forced array packing
+declare module "tslib" {
+    function __spreadArray(to: any[], from: any[]): any[];
+}