From fb0bdb9379489b479e1e7b35ca558991360cd57a Mon Sep 17 00:00:00 2001
From: pizzacat83 <17941141+pizzacat83@users.noreply.github.com>
Date: Sat, 29 Feb 2020 01:23:28 +0900
Subject: [PATCH] support 'in' type guard of intersections

---
 src/compiler/checker.ts                       |  2 +-
 .../reference/inKeywordTypeguard.errors.txt   | 11 +++++++-
 .../baselines/reference/inKeywordTypeguard.js | 19 +++++++++++++-
 .../reference/inKeywordTypeguard.symbols      | 23 +++++++++++++++++
 .../reference/inKeywordTypeguard.types        | 25 +++++++++++++++++++
 tests/cases/compiler/inKeywordTypeguard.ts    | 10 +++++++-
 6 files changed, 86 insertions(+), 4 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 1b2e6931e02c4..0b3dd1974ce6c 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20028,7 +20028,7 @@ namespace ts {
             }
 
             function narrowByInKeyword(type: Type, literal: LiteralExpression, assumeTrue: boolean) {
-                if (type.flags & (TypeFlags.Union | TypeFlags.Object) || isThisTypeParameter(type)) {
+                if (type.flags & (TypeFlags.Union | TypeFlags.Object | TypeFlags.Intersection) || isThisTypeParameter(type)) {
                     const propName = escapeLeadingUnderscores(literal.text);
                     return filterType(type, t => isTypePresencePossible(t, propName, assumeTrue));
                 }
diff --git a/tests/baselines/reference/inKeywordTypeguard.errors.txt b/tests/baselines/reference/inKeywordTypeguard.errors.txt
index 914daf42a7e98..f5885acfc8835 100644
--- a/tests/baselines/reference/inKeywordTypeguard.errors.txt
+++ b/tests/baselines/reference/inKeywordTypeguard.errors.txt
@@ -156,4 +156,13 @@ tests/cases/compiler/inKeywordTypeguard.ts(94,26): error TS2339: Property 'a' do
 !!! error TS2339: Property 'a' does not exist on type 'never'.
             }
         }
-    }
\ No newline at end of file
+    }
+    
+    function positiveIntersectionTest(x: { a: string } & { b: string }) {
+        if ("a" in x) {
+            let s: string = x.a;
+        } else {
+            let n: never = x;
+        }
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/inKeywordTypeguard.js b/tests/baselines/reference/inKeywordTypeguard.js
index 41ad27f96dff5..83499d7f54e3d 100644
--- a/tests/baselines/reference/inKeywordTypeguard.js
+++ b/tests/baselines/reference/inKeywordTypeguard.js
@@ -95,7 +95,16 @@ class UnreachableCodeDetection {
             let y = this.a;
         }
     }
-}
+}
+
+function positiveIntersectionTest(x: { a: string } & { b: string }) {
+    if ("a" in x) {
+        let s: string = x.a;
+    } else {
+        let n: never = x;
+    }
+}
+
 
 //// [inKeywordTypeguard.js]
 var A = /** @class */ (function () {
@@ -228,3 +237,11 @@ var UnreachableCodeDetection = /** @class */ (function () {
     };
     return UnreachableCodeDetection;
 }());
+function positiveIntersectionTest(x) {
+    if ("a" in x) {
+        var s = x.a;
+    }
+    else {
+        var n = x;
+    }
+}
diff --git a/tests/baselines/reference/inKeywordTypeguard.symbols b/tests/baselines/reference/inKeywordTypeguard.symbols
index c73f6f4901de5..ff79a4aa54efb 100644
--- a/tests/baselines/reference/inKeywordTypeguard.symbols
+++ b/tests/baselines/reference/inKeywordTypeguard.symbols
@@ -239,3 +239,26 @@ class UnreachableCodeDetection {
         }
     }
 }
+
+function positiveIntersectionTest(x: { a: string } & { b: string }) {
+>positiveIntersectionTest : Symbol(positiveIntersectionTest, Decl(inKeywordTypeguard.ts, 96, 1))
+>x : Symbol(x, Decl(inKeywordTypeguard.ts, 98, 34))
+>a : Symbol(a, Decl(inKeywordTypeguard.ts, 98, 38))
+>b : Symbol(b, Decl(inKeywordTypeguard.ts, 98, 54))
+
+    if ("a" in x) {
+>x : Symbol(x, Decl(inKeywordTypeguard.ts, 98, 34))
+
+        let s: string = x.a;
+>s : Symbol(s, Decl(inKeywordTypeguard.ts, 100, 11))
+>x.a : Symbol(a, Decl(inKeywordTypeguard.ts, 98, 38))
+>x : Symbol(x, Decl(inKeywordTypeguard.ts, 98, 34))
+>a : Symbol(a, Decl(inKeywordTypeguard.ts, 98, 38))
+
+    } else {
+        let n: never = x;
+>n : Symbol(n, Decl(inKeywordTypeguard.ts, 102, 11))
+>x : Symbol(x, Decl(inKeywordTypeguard.ts, 98, 34))
+    }
+}
+
diff --git a/tests/baselines/reference/inKeywordTypeguard.types b/tests/baselines/reference/inKeywordTypeguard.types
index 39c4054057838..ccb27f5c9b698 100644
--- a/tests/baselines/reference/inKeywordTypeguard.types
+++ b/tests/baselines/reference/inKeywordTypeguard.types
@@ -297,3 +297,28 @@ class UnreachableCodeDetection {
         }
     }
 }
+
+function positiveIntersectionTest(x: { a: string } & { b: string }) {
+>positiveIntersectionTest : (x: { a: string; } & { b: string; }) => void
+>x : { a: string; } & { b: string; }
+>a : string
+>b : string
+
+    if ("a" in x) {
+>"a" in x : boolean
+>"a" : "a"
+>x : { a: string; } & { b: string; }
+
+        let s: string = x.a;
+>s : string
+>x.a : string
+>x : { a: string; } & { b: string; }
+>a : string
+
+    } else {
+        let n: never = x;
+>n : never
+>x : never
+    }
+}
+
diff --git a/tests/cases/compiler/inKeywordTypeguard.ts b/tests/cases/compiler/inKeywordTypeguard.ts
index bbab20afc6f41..620aa401b252e 100644
--- a/tests/cases/compiler/inKeywordTypeguard.ts
+++ b/tests/cases/compiler/inKeywordTypeguard.ts
@@ -94,4 +94,12 @@ class UnreachableCodeDetection {
             let y = this.a;
         }
     }
-}
\ No newline at end of file
+}
+
+function positiveIntersectionTest(x: { a: string } & { b: string }) {
+    if ("a" in x) {
+        let s: string = x.a;
+    } else {
+        let n: never = x;
+    }
+}