From 6911acf80b712051db3833162eb68c3d3f79d13c Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Thu, 2 Nov 2017 14:28:46 -0700
Subject: [PATCH 1/2] Remove freshness from literal types in intersections

---
 src/compiler/checker.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 09354d957a3..7c8386e5580 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7589,11 +7589,11 @@ namespace ts {
             }
         }
 
-        // Add the given types to the given type set. Order is preserved, duplicates are removed,
-        // and nested types of the given kind are flattened into the set.
+        // Add the given types to the given type set. Order is preserved, freshness is removed from literal
+        // types, duplicates are removed, and nested types of the given kind are flattened into the set.
         function addTypesToIntersection(typeSet: TypeSet, types: Type[]) {
             for (const type of types) {
-                addTypeToIntersection(typeSet, type);
+                addTypeToIntersection(typeSet, getRegularTypeOfLiteralType(type));
             }
         }
 

From 18b5ade05d8ddfb9cce0d9d750a1da394337c904 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Thu, 2 Nov 2017 14:48:34 -0700
Subject: [PATCH 2/2] Add regression test

---
 .../freshLiteralTypesInIntersections.js       | 13 ++++++++
 .../freshLiteralTypesInIntersections.symbols  | 23 ++++++++++++++
 .../freshLiteralTypesInIntersections.types    | 30 +++++++++++++++++++
 .../freshLiteralTypesInIntersections.ts       |  7 +++++
 4 files changed, 73 insertions(+)
 create mode 100644 tests/baselines/reference/freshLiteralTypesInIntersections.js
 create mode 100644 tests/baselines/reference/freshLiteralTypesInIntersections.symbols
 create mode 100644 tests/baselines/reference/freshLiteralTypesInIntersections.types
 create mode 100644 tests/cases/compiler/freshLiteralTypesInIntersections.ts

diff --git a/tests/baselines/reference/freshLiteralTypesInIntersections.js b/tests/baselines/reference/freshLiteralTypesInIntersections.js
new file mode 100644
index 00000000000..633a2200380
--- /dev/null
+++ b/tests/baselines/reference/freshLiteralTypesInIntersections.js
@@ -0,0 +1,13 @@
+//// [freshLiteralTypesInIntersections.ts]
+// Repro from #19657
+
+declare function func<A extends string, B extends A>(a: A, b: B[]): (ab: A & B) => void;
+const q = func("x" as "x" | "y", ["x"]);
+q("x");
+
+
+//// [freshLiteralTypesInIntersections.js]
+"use strict";
+// Repro from #19657
+var q = func("x", ["x"]);
+q("x");
diff --git a/tests/baselines/reference/freshLiteralTypesInIntersections.symbols b/tests/baselines/reference/freshLiteralTypesInIntersections.symbols
new file mode 100644
index 00000000000..b16f90407b4
--- /dev/null
+++ b/tests/baselines/reference/freshLiteralTypesInIntersections.symbols
@@ -0,0 +1,23 @@
+=== tests/cases/compiler/freshLiteralTypesInIntersections.ts ===
+// Repro from #19657
+
+declare function func<A extends string, B extends A>(a: A, b: B[]): (ab: A & B) => void;
+>func : Symbol(func, Decl(freshLiteralTypesInIntersections.ts, 0, 0))
+>A : Symbol(A, Decl(freshLiteralTypesInIntersections.ts, 2, 22))
+>B : Symbol(B, Decl(freshLiteralTypesInIntersections.ts, 2, 39))
+>A : Symbol(A, Decl(freshLiteralTypesInIntersections.ts, 2, 22))
+>a : Symbol(a, Decl(freshLiteralTypesInIntersections.ts, 2, 53))
+>A : Symbol(A, Decl(freshLiteralTypesInIntersections.ts, 2, 22))
+>b : Symbol(b, Decl(freshLiteralTypesInIntersections.ts, 2, 58))
+>B : Symbol(B, Decl(freshLiteralTypesInIntersections.ts, 2, 39))
+>ab : Symbol(ab, Decl(freshLiteralTypesInIntersections.ts, 2, 69))
+>A : Symbol(A, Decl(freshLiteralTypesInIntersections.ts, 2, 22))
+>B : Symbol(B, Decl(freshLiteralTypesInIntersections.ts, 2, 39))
+
+const q = func("x" as "x" | "y", ["x"]);
+>q : Symbol(q, Decl(freshLiteralTypesInIntersections.ts, 3, 5))
+>func : Symbol(func, Decl(freshLiteralTypesInIntersections.ts, 0, 0))
+
+q("x");
+>q : Symbol(q, Decl(freshLiteralTypesInIntersections.ts, 3, 5))
+
diff --git a/tests/baselines/reference/freshLiteralTypesInIntersections.types b/tests/baselines/reference/freshLiteralTypesInIntersections.types
new file mode 100644
index 00000000000..b693a8c2c3f
--- /dev/null
+++ b/tests/baselines/reference/freshLiteralTypesInIntersections.types
@@ -0,0 +1,30 @@
+=== tests/cases/compiler/freshLiteralTypesInIntersections.ts ===
+// Repro from #19657
+
+declare function func<A extends string, B extends A>(a: A, b: B[]): (ab: A & B) => void;
+>func : <A extends string, B extends A>(a: A, b: B[]) => (ab: A & B) => void
+>A : A
+>B : B
+>A : A
+>a : A
+>A : A
+>b : B[]
+>B : B
+>ab : A & B
+>A : A
+>B : B
+
+const q = func("x" as "x" | "y", ["x"]);
+>q : (ab: "x") => void
+>func("x" as "x" | "y", ["x"]) : (ab: "x") => void
+>func : <A extends string, B extends A>(a: A, b: B[]) => (ab: A & B) => void
+>"x" as "x" | "y" : "x" | "y"
+>"x" : "x"
+>["x"] : "x"[]
+>"x" : "x"
+
+q("x");
+>q("x") : void
+>q : (ab: "x") => void
+>"x" : "x"
+
diff --git a/tests/cases/compiler/freshLiteralTypesInIntersections.ts b/tests/cases/compiler/freshLiteralTypesInIntersections.ts
new file mode 100644
index 00000000000..b1e73974426
--- /dev/null
+++ b/tests/cases/compiler/freshLiteralTypesInIntersections.ts
@@ -0,0 +1,7 @@
+// @strict: true
+
+// Repro from #19657
+
+declare function func<A extends string, B extends A>(a: A, b: B[]): (ab: A & B) => void;
+const q = func("x" as "x" | "y", ["x"]);
+q("x");