From 2e5a39a3cebfcd4a712bd1a72ab9962acbe75d3d Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Mon, 8 Oct 2018 16:35:03 -0700
Subject: [PATCH] Error when indexing out of bounds in a tuple or union of
 tuples

---
 src/compiler/checker.ts              | 14 ++++++--------
 src/compiler/diagnosticMessages.json |  4 ----
 2 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 3b2c4efc662..33d23bd11ee 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -9312,7 +9312,12 @@ namespace ts {
                         propType;
                 }
                 if (everyType(objectType, isTupleType) && isNumericLiteralName(propName) && +propName >= 0) {
-                    return mapType(objectType, t => getRestTypeOfTupleType(<TupleTypeReference>t) || undefinedType);
+                    const restType = mapType(objectType, t => getRestTypeOfTupleType(<TupleTypeReference>t) || undefinedType);
+                    if (restType === undefinedType && accessNode) {
+                        const indexNode = accessNode.kind === SyntaxKind.ElementAccessExpression ? accessNode.argumentExpression : accessNode.indexType;
+                        error(indexNode, Diagnostics.Property_0_does_not_exist_on_type_1, unescapeLeadingUnderscores(propName), typeToString(objectType));
+                    }
+                    return restType;
                 }
             }
             if (!(indexType.flags & TypeFlags.Nullable) && isTypeAssignableToKind(indexType, TypeFlags.StringLike | TypeFlags.NumberLike | TypeFlags.ESSymbolLike)) {
@@ -18964,13 +18969,6 @@ namespace ts {
                 error(indexExpression, Diagnostics.A_const_enum_member_can_only_be_accessed_using_a_string_literal);
                 return errorType;
             }
-            if (isTupleType(objectType) && !objectType.target.hasRestElement && isNumericLiteral(indexExpression)) {
-                const index = +indexExpression.text;
-                const length = getTypeReferenceArity(objectType);
-                if (index >= length) {
-                    error(indexExpression, Diagnostics.Index_0_is_out_of_bounds_in_tuple_of_length_1, index, length);
-                }
-            }
 
             return checkIndexedAccessIndexType(getIndexedAccessType(objectType, isForInVariableForNumericPropertyNames(indexExpression) ? numberType : indexType, node), node);
         }
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index ce1ccf17145..01d95bc2b85 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -2481,10 +2481,6 @@
         "category": "Error",
         "code": 2732
     },
-    "Index '{0}' is out-of-bounds in tuple of length {1}.": {
-        "category": "Error",
-        "code": 2733
-    },
     "It is highly likely that you are missing a semicolon.": {
         "category": "Error",
         "code": 2734