chore(sdk): add out of bounds exception to string.at (#3312)

Adds exception to `string.at` if index is out of bounds.

closes #3240 

## Checklist

- [x] Title matches [Winglang's style guide](https://www.winglang.io/contributing/start-here/pull_requests#how-are-pull-request-titles-formatted)
- [x] Description explains motivation and solution
- [x] Tests added (always)
- [ ] Docs updated (only required for features)
- [ ] Added `pr/e2e-full` label if this feature requires end-to-end testing

*By submitting this pull request, I confirm that my contribution is made under the terms of the [Monada Contribution License](https://www.winglang.io/terms-and-policies/contribution-license.html)*.

examples/tests/sdk_tests/std/string.w

@@ -39,19 +39,28 @@ test "length" {
 //-----------------------------------------------------------------------------
 // at()
 
+let INDEX_OUT_OF_BOUNDS_ERROR = "index out of bounds";
+
 assert("boom".at(2) == "o");
 // Negative integers count back from the last string character.
 assert("boom".at(-4) == "b");
 assert("boom".at(-1) == "m");
+// Should throw an exception
+assertThrows(INDEX_OUT_OF_BOUNDS_ERROR, () => {
+  "boom".at(4);
+});
+assertThrows(INDEX_OUT_OF_BOUNDS_ERROR, () => {
+  "boom".at(-5);
+});
 
 test "at()" {
   assert("boom".at(0) == "b");
   // Negative integers count back from the last string character.
   assert("boom".at(-4) == "b");
   assert("boom".at(-1) == "m");
-
-  // Should throw an exception instead of returns undefined see issue #3240
-  // assert("boom".at(-10) == "m");
+  // Should throw an exception
+  try { "boom".at(4); } catch s { assert(s == INDEX_OUT_OF_BOUNDS_ERROR ); } // <-- Passes if no exception is thrown, see issue #3341
+  try { "boom".at(-5); } catch s { assert(s == INDEX_OUT_OF_BOUNDS_ERROR ); }
 }
 
 //-----------------------------------------------------------------------------

libs/wingsdk/src/std/string.ts

@@ -41,6 +41,8 @@ export class String {
   /**
    * Returns the character at the specified index.
    *
+   * @macro ((args) => { if ($args$ >= $self$.length || $args$ + $self$.length < 0) {throw new Error("index out of bounds")}; return $self$.at($args$) })($args$)
+   *
    * @param index position of the character.
    * @returns string at the specified index.
    */

tools/hangar/__snapshots__/test_corpus/sdk_tests/std/string.w_compile_tf-aws.md

@@ -126,17 +126,31 @@ module.exports = function({  }) {
 
 ## inflight.$Closure3.js
 ```js
-module.exports = function({  }) {
+module.exports = function({ $INDEX_OUT_OF_BOUNDS_ERROR }) {
   class $Closure3 {
     constructor({  }) {
       const $obj = (...args) => this.handle(...args);
       Object.setPrototypeOf($obj, this);
       return $obj;
     }
     async handle() {
-      {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(0) == \"b\"")})(((await "boom".at(0)) === "b"))};
-      {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(-4) == \"b\"")})(((await "boom".at((-4))) === "b"))};
-      {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(-1) == \"m\"")})(((await "boom".at((-1))) === "m"))};
+      {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(0) == \"b\"")})((((args) => { if (0 >= "boom".length || 0 + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at(0) })(0) === "b"))};
+      {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(-4) == \"b\"")})((((args) => { if ((-4) >= "boom".length || (-4) + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at((-4)) })((-4)) === "b"))};
+      {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(-1) == \"m\"")})((((args) => { if ((-1) >= "boom".length || (-1) + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at((-1)) })((-1)) === "m"))};
+      try {
+        ((args) => { if (4 >= "boom".length || 4 + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at(4) })(4);
+      }
+      catch ($error_s) {
+        const s = $error_s.message;
+        {((cond) => {if (!cond) throw new Error("assertion failed: s == INDEX_OUT_OF_BOUNDS_ERROR ")})((s === $INDEX_OUT_OF_BOUNDS_ERROR))};
+      }
+      try {
+        ((args) => { if ((-5) >= "boom".length || (-5) + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at((-5)) })((-5));
+      }
+      catch ($error_s) {
+        const s = $error_s.message;
+        {((cond) => {if (!cond) throw new Error("assertion failed: s == INDEX_OUT_OF_BOUNDS_ERROR ")})((s === $INDEX_OUT_OF_BOUNDS_ERROR))};
+      }
     }
   }
   return $Closure3;
@@ -1254,6 +1268,7 @@ class $Root extends $stdlib.std.Resource {
       static _toInflightType(context) {
         return $stdlib.core.NodeJsCode.fromInline(`
           require("./inflight.$Closure3.js")({
+            $INDEX_OUT_OF_BOUNDS_ERROR: ${context._lift(INDEX_OUT_OF_BOUNDS_ERROR)},
           })
         `);
       }
@@ -1268,6 +1283,12 @@ class $Root extends $stdlib.std.Resource {
           })())
         `);
       }
+      _registerBind(host, ops) {
+        if (ops.includes("handle")) {
+          $Closure3._registerBindObject(INDEX_OUT_OF_BOUNDS_ERROR, host, []);
+        }
+        super._registerBind(host, ops);
+      }
     }
     class $Closure4 extends $stdlib.std.Resource {
       constructor(scope, id, ) {
@@ -1530,9 +1551,16 @@ class $Root extends $stdlib.std.Resource {
     {((cond) => {if (!cond) throw new Error("assertion failed: \"hello\".length == 5")})(("hello".length === 5))};
     {((cond) => {if (!cond) throw new Error("assertion failed: \"\".length == 0")})(("".length === 0))};
     this.node.root.new("@winglang/sdk.std.Test",std.Test,this,"test:length",new $Closure2(this,"$Closure2"));
-    {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(2) == \"o\"")})((("boom".at(2)) === "o"))};
-    {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(-4) == \"b\"")})((("boom".at((-4))) === "b"))};
-    {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(-1) == \"m\"")})((("boom".at((-1))) === "m"))};
+    const INDEX_OUT_OF_BOUNDS_ERROR = "index out of bounds";
+    {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(2) == \"o\"")})((((args) => { if (2 >= "boom".length || 2 + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at(2) })(2) === "o"))};
+    {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(-4) == \"b\"")})((((args) => { if ((-4) >= "boom".length || (-4) + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at((-4)) })((-4)) === "b"))};
+    {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".at(-1) == \"m\"")})((((args) => { if ((-1) >= "boom".length || (-1) + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at((-1)) })((-1)) === "m"))};
+    (assertThrows(INDEX_OUT_OF_BOUNDS_ERROR,(() => {
+      ((args) => { if (4 >= "boom".length || 4 + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at(4) })(4);
+    })));
+    (assertThrows(INDEX_OUT_OF_BOUNDS_ERROR,(() => {
+      ((args) => { if ((-5) >= "boom".length || (-5) + "boom".length < 0) {throw new Error("index out of bounds")}; return "boom".at((-5)) })((-5));
+    })));
     this.node.root.new("@winglang/sdk.std.Test",std.Test,this,"test:at()",new $Closure3(this,"$Closure3"));
     {((cond) => {if (!cond) throw new Error("assertion failed: \"boom\".concat(\"boom\") == \"boomboom\"")})((("boom".concat("boom")) === "boomboom"))};
     this.node.root.new("@winglang/sdk.std.Test",std.Test,this,"test:concat()",new $Closure4(this,"$Closure4"));

tools/hangar/__snapshots__/test_corpus/valid/std_string.w_compile_tf-aws.md

@@ -189,7 +189,7 @@ class $Root extends $stdlib.std.Resource {
     const s1 = "some string";
     const s2 = "s are immutable";
     {((cond) => {if (!cond) throw new Error("assertion failed: s1.length == 11")})((s1.length === 11))};
-    {((cond) => {if (!cond) throw new Error("assertion failed: s1.at(7) == \"r\"")})(((s1.at(7)) === "r"))};
+    {((cond) => {if (!cond) throw new Error("assertion failed: s1.at(7) == \"r\"")})((((args) => { if (7 >= s1.length || 7 + s1.length < 0) {throw new Error("index out of bounds")}; return s1.at(7) })(7) === "r"))};
     {((cond) => {if (!cond) throw new Error("assertion failed: s1.concat(s2) == \"some strings are immutable\"")})(((s1.concat(s2)) === "some strings are immutable"))};
     {((cond) => {if (!cond) throw new Error("assertion failed: s1.contains(\"some\")")})(s1.includes("some"))};
     {((cond) => {if (!cond) throw new Error("assertion failed: !\"some\".contains(s1)")})((!"some".includes(s1)))};