From 27c8c840eda5c86c1b1333567bc41be10a31312a Mon Sep 17 00:00:00 2001
From: Andrew Branch <andrew@wheream.io>
Date: Thu, 22 Apr 2021 09:11:16 -0700
Subject: [PATCH 1/2] Add test

---
 tests/cases/compiler/destructuringFromUnionSpread.ts | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 tests/cases/compiler/destructuringFromUnionSpread.ts

diff --git a/tests/cases/compiler/destructuringFromUnionSpread.ts b/tests/cases/compiler/destructuringFromUnionSpread.ts
new file mode 100644
index 0000000000000..92ef2e369aa9b
--- /dev/null
+++ b/tests/cases/compiler/destructuringFromUnionSpread.ts
@@ -0,0 +1,11 @@
+interface A { a: string }
+interface B { b: number }
+
+function foo(x: A | B) {
+    const { a } = { ...x } // no error?! 
+    // const a: string | undefined
+    a?.toUpperCase();
+}
+
+const x = { a: 1, b: 2 }
+foo(x); // a.toUpperCase is not a function, oops

From 2950db90ed7c84a310e5e7cca6b7771e56ead36e Mon Sep 17 00:00:00 2001
From: Andrew Branch <andrew@wheream.io>
Date: Thu, 22 Apr 2021 16:32:43 -0700
Subject: [PATCH 2/2] =?UTF-8?q?Don=E2=80=99t=20allow=20an=20object=20liter?=
 =?UTF-8?q?al=20with=20a=20spread=20as=20a=20fallback=20for=20destructurin?=
 =?UTF-8?q?g=20a=20property=20not=20present=20in=20all=20constituents?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 src/compiler/checker.ts                       |  2 +-
 .../destructuringFromUnionSpread.errors.txt   | 12 +++++++++++
 .../reference/destructuringFromUnionSpread.js | 21 +++++++++++++++++++
 .../destructuringFromUnionSpread.symbols      | 18 ++++++++++++++++
 .../destructuringFromUnionSpread.types        | 15 +++++++++++++
 .../compiler/destructuringFromUnionSpread.ts  | 10 ++-------
 6 files changed, 69 insertions(+), 9 deletions(-)
 create mode 100644 tests/baselines/reference/destructuringFromUnionSpread.errors.txt
 create mode 100644 tests/baselines/reference/destructuringFromUnionSpread.js
 create mode 100644 tests/baselines/reference/destructuringFromUnionSpread.symbols
 create mode 100644 tests/baselines/reference/destructuringFromUnionSpread.types

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 3cc7ff57f8cba..750d3232987c8 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11698,7 +11698,7 @@ namespace ts {
                             checkFlags |= CheckFlags.WritePartial | (indexInfo.isReadonly ? CheckFlags.Readonly : 0);
                             indexTypes = append(indexTypes, isTupleType(type) ? getRestTypeOfTupleType(type) || undefinedType : indexInfo.type);
                         }
-                        else if (isObjectLiteralType(type)) {
+                        else if (isObjectLiteralType(type) && !(getObjectFlags(type) & ObjectFlags.ContainsSpread)) {
                             checkFlags |= CheckFlags.WritePartial;
                             indexTypes = append(indexTypes, undefinedType);
                         }
diff --git a/tests/baselines/reference/destructuringFromUnionSpread.errors.txt b/tests/baselines/reference/destructuringFromUnionSpread.errors.txt
new file mode 100644
index 0000000000000..f329b8a8d38f0
--- /dev/null
+++ b/tests/baselines/reference/destructuringFromUnionSpread.errors.txt
@@ -0,0 +1,12 @@
+tests/cases/compiler/destructuringFromUnionSpread.ts(5,9): error TS2525: Initializer provides no value for this binding element and the binding element has no default value.
+
+
+==== tests/cases/compiler/destructuringFromUnionSpread.ts (1 errors) ====
+    interface A { a: string }
+    interface B { b: number }
+    
+    declare const x: A | B;
+    const { a } = { ...x } // error
+            ~
+!!! error TS2525: Initializer provides no value for this binding element and the binding element has no default value.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/destructuringFromUnionSpread.js b/tests/baselines/reference/destructuringFromUnionSpread.js
new file mode 100644
index 0000000000000..a67e1a711260d
--- /dev/null
+++ b/tests/baselines/reference/destructuringFromUnionSpread.js
@@ -0,0 +1,21 @@
+//// [destructuringFromUnionSpread.ts]
+interface A { a: string }
+interface B { b: number }
+
+declare const x: A | B;
+const { a } = { ...x } // error
+
+
+//// [destructuringFromUnionSpread.js]
+var __assign = (this && this.__assign) || function () {
+    __assign = Object.assign || function(t) {
+        for (var s, i = 1, n = arguments.length; i < n; i++) {
+            s = arguments[i];
+            for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
+                t[p] = s[p];
+        }
+        return t;
+    };
+    return __assign.apply(this, arguments);
+};
+var a = __assign({}, x).a; // error
diff --git a/tests/baselines/reference/destructuringFromUnionSpread.symbols b/tests/baselines/reference/destructuringFromUnionSpread.symbols
new file mode 100644
index 0000000000000..88737096bce93
--- /dev/null
+++ b/tests/baselines/reference/destructuringFromUnionSpread.symbols
@@ -0,0 +1,18 @@
+=== tests/cases/compiler/destructuringFromUnionSpread.ts ===
+interface A { a: string }
+>A : Symbol(A, Decl(destructuringFromUnionSpread.ts, 0, 0))
+>a : Symbol(A.a, Decl(destructuringFromUnionSpread.ts, 0, 13))
+
+interface B { b: number }
+>B : Symbol(B, Decl(destructuringFromUnionSpread.ts, 0, 25))
+>b : Symbol(B.b, Decl(destructuringFromUnionSpread.ts, 1, 13))
+
+declare const x: A | B;
+>x : Symbol(x, Decl(destructuringFromUnionSpread.ts, 3, 13))
+>A : Symbol(A, Decl(destructuringFromUnionSpread.ts, 0, 0))
+>B : Symbol(B, Decl(destructuringFromUnionSpread.ts, 0, 25))
+
+const { a } = { ...x } // error
+>a : Symbol(a, Decl(destructuringFromUnionSpread.ts, 4, 7))
+>x : Symbol(x, Decl(destructuringFromUnionSpread.ts, 3, 13))
+
diff --git a/tests/baselines/reference/destructuringFromUnionSpread.types b/tests/baselines/reference/destructuringFromUnionSpread.types
new file mode 100644
index 0000000000000..e24656790e167
--- /dev/null
+++ b/tests/baselines/reference/destructuringFromUnionSpread.types
@@ -0,0 +1,15 @@
+=== tests/cases/compiler/destructuringFromUnionSpread.ts ===
+interface A { a: string }
+>a : string
+
+interface B { b: number }
+>b : number
+
+declare const x: A | B;
+>x : A | B
+
+const { a } = { ...x } // error
+>a : any
+>{ ...x } : { a: any; } | { a: any; b: number; }
+>x : A | B
+
diff --git a/tests/cases/compiler/destructuringFromUnionSpread.ts b/tests/cases/compiler/destructuringFromUnionSpread.ts
index 92ef2e369aa9b..2e73fa6813443 100644
--- a/tests/cases/compiler/destructuringFromUnionSpread.ts
+++ b/tests/cases/compiler/destructuringFromUnionSpread.ts
@@ -1,11 +1,5 @@
 interface A { a: string }
 interface B { b: number }
 
-function foo(x: A | B) {
-    const { a } = { ...x } // no error?! 
-    // const a: string | undefined
-    a?.toUpperCase();
-}
-
-const x = { a: 1, b: 2 }
-foo(x); // a.toUpperCase is not a function, oops
+declare const x: A | B;
+const { a } = { ...x } // error