Error on excess spread arguments

sandersn · sandersn · commit 8657dc10a740 · 2017-11-16T09:31:50.000-08:00
Make the *technically* correct construction illegal:

```ts
declare function f(n: number): void;
declare var ns: number[];
f(1, ...ns);
```

This call only makes sense if `ns = []`, but in that case, why pass
`ns` at all? Allowing this call masks other errors when functions are
refactored to have fewer parameters, or to stop using rest parameters:

```ts
declare function old(...ns: number[]): void;
declare function new(ns: number | number[]): void;
old(1, ...ns); // Fine!
new(1, ...ns); // Should error!
```

This change the error for excess spread arguments to be more
understandable:

"Expected 3 arguments, but got least 4".

Previously the error would have been
"Expected 3 argument, but got at least 3", which is, again, technically
correct, but not understandable.
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -15790,10 +15790,10 @@ namespace ts {
                 return false;
             }
 
-            // If spread arguments are present, check that they correspond to a rest parameter. If so, no
-            // further checking is necessary.
+            // If a spread argument is present, check that it corresponds to a rest parameter or at least that it's in the valid range.
             if (spreadArgIndex >= 0) {
-                return isRestParameterIndex(signature, spreadArgIndex) || spreadArgIndex >= signature.minArgumentCount;
+                return isRestParameterIndex(signature, spreadArgIndex) ||
+                    signature.minArgumentCount <= spreadArgIndex && spreadArgIndex < signature.parameters.length;
             }
 
             // Too many arguments implies incorrect arity.
@@ -16501,7 +16501,10 @@ namespace ts {
                 const paramCount = hasRestParameter ? min :
                     min < max ? min + "-" + max :
                     min;
-                const argCount = args.length - (hasSpreadArgument ? 1 : 0);
+                let argCount = args.length;
+                if (argCount <= max && hasSpreadArgument) {
+                    argCount--;
+                }
                 const error = hasRestParameter && hasSpreadArgument ? Diagnostics.Expected_at_least_0_arguments_but_got_a_minimum_of_1 :
                     hasRestParameter ? Diagnostics.Expected_at_least_0_arguments_but_got_1 :
                     hasSpreadArgument ? Diagnostics.Expected_0_arguments_but_got_a_minimum_of_1 :
