From 07d3a2ec7e4bba39df98a9f1bd16bc04112b9716 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wewigham@microsoft.com>
Date: Wed, 23 Oct 2019 16:01:25 -0700
Subject: [PATCH] Do not consider element accesses which are neither statically
 bindable nor late bound as special assignments (#34679)

---
 src/compiler/utilities.ts                           |  8 +++++---
 .../jsNegativeElementAccessNotBound.symbols         |  7 +++++++
 .../reference/jsNegativeElementAccessNotBound.types | 13 +++++++++++++
 .../compiler/jsNegativeElementAccessNotBound.ts     |  6 ++++++
 4 files changed, 31 insertions(+), 3 deletions(-)
 create mode 100644 tests/baselines/reference/jsNegativeElementAccessNotBound.symbols
 create mode 100644 tests/baselines/reference/jsNegativeElementAccessNotBound.types
 create mode 100644 tests/cases/compiler/jsNegativeElementAccessNotBound.ts

diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index e86f79b360a..12b11eeae29 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -2115,7 +2115,7 @@ namespace ts {
         if (expr.operatorToken.kind !== SyntaxKind.EqualsToken || !isAccessExpression(expr.left)) {
             return AssignmentDeclarationKind.None;
         }
-        if (isBindableStaticNameExpression(expr.left.expression) && getElementOrPropertyAccessName(expr.left) === "prototype" && isObjectLiteralExpression(getInitializerOfBinaryExpression(expr))) {
+        if (isBindableStaticNameExpression(expr.left.expression, /*excludeThisKeyword*/ true) && getElementOrPropertyAccessName(expr.left) === "prototype" && isObjectLiteralExpression(getInitializerOfBinaryExpression(expr))) {
             // F.prototype = { ... }
             return AssignmentDeclarationKind.Prototype;
         }
@@ -2183,8 +2183,10 @@ namespace ts {
                 // exports.name = expr OR module.exports.name = expr OR exports["name"] = expr ...
                 return AssignmentDeclarationKind.ExportsProperty;
             }
-            // F.G...x = expr
-            return AssignmentDeclarationKind.Property;
+            if (isBindableStaticNameExpression(lhs, /*excludeThisKeyword*/ true) || (isElementAccessExpression(lhs) && isDynamicName(lhs) && lhs.expression.kind !== SyntaxKind.ThisKeyword)) {
+                // F.G...x = expr
+                return AssignmentDeclarationKind.Property;
+            }
         }
 
         return AssignmentDeclarationKind.None;
diff --git a/tests/baselines/reference/jsNegativeElementAccessNotBound.symbols b/tests/baselines/reference/jsNegativeElementAccessNotBound.symbols
new file mode 100644
index 00000000000..d8ff3f52e23
--- /dev/null
+++ b/tests/baselines/reference/jsNegativeElementAccessNotBound.symbols
@@ -0,0 +1,7 @@
+=== tests/cases/compiler/jsNegativeELementAccessNotBound.js ===
+var indexMap = {};
+>indexMap : Symbol(indexMap, Decl(jsNegativeELementAccessNotBound.js, 0, 3))
+
+indexMap[-1] = 0;
+>indexMap : Symbol(indexMap, Decl(jsNegativeELementAccessNotBound.js, 0, 3))
+
diff --git a/tests/baselines/reference/jsNegativeElementAccessNotBound.types b/tests/baselines/reference/jsNegativeElementAccessNotBound.types
new file mode 100644
index 00000000000..dbd5d4c005d
--- /dev/null
+++ b/tests/baselines/reference/jsNegativeElementAccessNotBound.types
@@ -0,0 +1,13 @@
+=== tests/cases/compiler/jsNegativeELementAccessNotBound.js ===
+var indexMap = {};
+>indexMap : {}
+>{} : {}
+
+indexMap[-1] = 0;
+>indexMap[-1] = 0 : 0
+>indexMap[-1] : any
+>indexMap : {}
+>-1 : -1
+>1 : 1
+>0 : 0
+
diff --git a/tests/cases/compiler/jsNegativeElementAccessNotBound.ts b/tests/cases/compiler/jsNegativeElementAccessNotBound.ts
new file mode 100644
index 00000000000..c7a204e578f
--- /dev/null
+++ b/tests/cases/compiler/jsNegativeElementAccessNotBound.ts
@@ -0,0 +1,6 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+// @filename: jsNegativeELementAccessNotBound.js
+var indexMap = {};
+indexMap[-1] = 0;