From 46ce0b2582c531d201c837dc579228281293b233 Mon Sep 17 00:00:00 2001
From: Andrew Branch <andrew@wheream.io>
Date: Thu, 1 Sep 2022 10:37:43 -0700
Subject: [PATCH] Use bidirectional comparability (aka comparability) in
 narrowing

---
 src/compiler/checker.ts                 |  2 +-
 tests/baselines/reference/50527.js      | 19 ++++++++++++++
 tests/baselines/reference/50527.symbols | 33 +++++++++++++++++++++++++
 tests/baselines/reference/50527.types   | 33 +++++++++++++++++++++++++
 tests/cases/compiler/50527.ts           | 13 ++++++++++
 5 files changed, 99 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/50527.js
 create mode 100644 tests/baselines/reference/50527.symbols
 create mode 100644 tests/baselines/reference/50527.types
 create mode 100644 tests/cases/compiler/50527.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index e911d7fe7d2a3..7b4b98217ce4a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -25096,7 +25096,7 @@ namespace ts {
                 const narrowedPropType = narrowType(propType);
                 return filterType(type, t => {
                     const discriminantType = getTypeOfPropertyOrIndexSignature(t, propName);
-                    return !(narrowedPropType.flags & TypeFlags.Never) && isTypeComparableTo(narrowedPropType, discriminantType);
+                    return !(narrowedPropType.flags & TypeFlags.Never) && areTypesComparable(narrowedPropType, discriminantType);
                 });
             }
 
diff --git a/tests/baselines/reference/50527.js b/tests/baselines/reference/50527.js
new file mode 100644
index 0000000000000..464861a224d1e
--- /dev/null
+++ b/tests/baselines/reference/50527.js
@@ -0,0 +1,19 @@
+//// [50527.ts]
+type S = 
+| { type: 'string', value: string } 
+| { type: 'number', value: number } 
+| { type: 'unknown', value: unknown }
+| { value: undefined };
+
+declare var s: S
+
+if (s.value !== undefined) {
+  s;
+}
+
+
+//// [50527.js]
+"use strict";
+if (s.value !== undefined) {
+    s;
+}
diff --git a/tests/baselines/reference/50527.symbols b/tests/baselines/reference/50527.symbols
new file mode 100644
index 0000000000000..82e4f791e50aa
--- /dev/null
+++ b/tests/baselines/reference/50527.symbols
@@ -0,0 +1,33 @@
+=== tests/cases/compiler/50527.ts ===
+type S = 
+>S : Symbol(S, Decl(50527.ts, 0, 0))
+
+| { type: 'string', value: string } 
+>type : Symbol(type, Decl(50527.ts, 1, 3))
+>value : Symbol(value, Decl(50527.ts, 1, 19))
+
+| { type: 'number', value: number } 
+>type : Symbol(type, Decl(50527.ts, 2, 3))
+>value : Symbol(value, Decl(50527.ts, 2, 19))
+
+| { type: 'unknown', value: unknown }
+>type : Symbol(type, Decl(50527.ts, 3, 3))
+>value : Symbol(value, Decl(50527.ts, 3, 20))
+
+| { value: undefined };
+>value : Symbol(value, Decl(50527.ts, 4, 3))
+
+declare var s: S
+>s : Symbol(s, Decl(50527.ts, 6, 11))
+>S : Symbol(S, Decl(50527.ts, 0, 0))
+
+if (s.value !== undefined) {
+>s.value : Symbol(value, Decl(50527.ts, 1, 19), Decl(50527.ts, 2, 19), Decl(50527.ts, 3, 20), Decl(50527.ts, 4, 3))
+>s : Symbol(s, Decl(50527.ts, 6, 11))
+>value : Symbol(value, Decl(50527.ts, 1, 19), Decl(50527.ts, 2, 19), Decl(50527.ts, 3, 20), Decl(50527.ts, 4, 3))
+>undefined : Symbol(undefined)
+
+  s;
+>s : Symbol(s, Decl(50527.ts, 6, 11))
+}
+
diff --git a/tests/baselines/reference/50527.types b/tests/baselines/reference/50527.types
new file mode 100644
index 0000000000000..aef6d2fea0f85
--- /dev/null
+++ b/tests/baselines/reference/50527.types
@@ -0,0 +1,33 @@
+=== tests/cases/compiler/50527.ts ===
+type S = 
+>S : { type: 'string'; value: string; } | { type: 'number'; value: number; } | { type: 'unknown'; value: unknown; } | { value: undefined; }
+
+| { type: 'string', value: string } 
+>type : "string"
+>value : string
+
+| { type: 'number', value: number } 
+>type : "number"
+>value : number
+
+| { type: 'unknown', value: unknown }
+>type : "unknown"
+>value : unknown
+
+| { value: undefined };
+>value : undefined
+
+declare var s: S
+>s : S
+
+if (s.value !== undefined) {
+>s.value !== undefined : boolean
+>s.value : unknown
+>s : S
+>value : unknown
+>undefined : undefined
+
+  s;
+>s : { type: "string"; value: string; } | { type: "number"; value: number; } | { type: "unknown"; value: unknown; }
+}
+
diff --git a/tests/cases/compiler/50527.ts b/tests/cases/compiler/50527.ts
new file mode 100644
index 0000000000000..19f1753b421c2
--- /dev/null
+++ b/tests/cases/compiler/50527.ts
@@ -0,0 +1,13 @@
+// @strict: true
+
+type S = 
+| { type: 'string', value: string } 
+| { type: 'number', value: number } 
+| { type: 'unknown', value: unknown }
+| { value: undefined };
+
+declare var s: S
+
+if (s.value !== undefined) {
+  s;
+}