From d3c572c1873e767ef6ce677a0b0b956f134e0802 Mon Sep 17 00:00:00 2001
From: Forbes Lindesay <forbes.lindesay@threadsstyling.com>
Date: Mon, 18 Feb 2019 13:20:19 +0000
Subject: [PATCH 1/2] Allow Boolean() to be used to perform a null check

---
 src/lib/es5.d.ts                                   |  2 +-
 .../expressions/typeGuards/typeGuardBoolean.ts     | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 tests/cases/conformance/expressions/typeGuards/typeGuardBoolean.ts

diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index 4112f5a2ae7d7..18a98d1507d26 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -513,7 +513,7 @@ interface Boolean {
 
 interface BooleanConstructor {
     new(value?: any): Boolean;
-    (value?: any): boolean;
+    <T>(value?: T): value is Exclude<T, false | null | undefined | '' | 0>;
     readonly prototype: Boolean;
 }
 
diff --git a/tests/cases/conformance/expressions/typeGuards/typeGuardBoolean.ts b/tests/cases/conformance/expressions/typeGuards/typeGuardBoolean.ts
new file mode 100644
index 0000000000000..3f2dde227ba8c
--- /dev/null
+++ b/tests/cases/conformance/expressions/typeGuards/typeGuardBoolean.ts
@@ -0,0 +1,14 @@
+// @strictNullChecks: true
+function test(strOrNull: string | null, strOrUndefined: string | undefined) {
+  var str: string = "original";
+  var nil: null;
+  if (!Boolean(strOrNull)) {
+      nil = strOrNull;
+  }
+  else {
+      str = strOrNull;
+  }
+  if (Boolean(strOrUndefined)) {
+      str = strOrUndefined;
+  }
+}

From 24e7e1c76023bd5084331b0b1942f01ac96d31a0 Mon Sep 17 00:00:00 2001
From: Forbes Lindesay <forbes.lindesay@threadsstyling.com>
Date: Mon, 18 Feb 2019 14:02:44 +0000
Subject: [PATCH 2/2] Add missing test case output

---
 tests/baselines/reference/typeGuardBoolean.js | 30 +++++++++++++
 .../reference/typeGuardBoolean.symbols        | 35 +++++++++++++++
 .../reference/typeGuardBoolean.types          | 44 +++++++++++++++++++
 3 files changed, 109 insertions(+)
 create mode 100644 tests/baselines/reference/typeGuardBoolean.js
 create mode 100644 tests/baselines/reference/typeGuardBoolean.symbols
 create mode 100644 tests/baselines/reference/typeGuardBoolean.types

diff --git a/tests/baselines/reference/typeGuardBoolean.js b/tests/baselines/reference/typeGuardBoolean.js
new file mode 100644
index 0000000000000..1bfe41983d83b
--- /dev/null
+++ b/tests/baselines/reference/typeGuardBoolean.js
@@ -0,0 +1,30 @@
+//// [typeGuardBoolean.ts]
+function test(strOrNull: string | null, strOrUndefined: string | undefined) {
+  var str: string = "original";
+  var nil: null;
+  if (!Boolean(strOrNull)) {
+      nil = strOrNull;
+  }
+  else {
+      str = strOrNull;
+  }
+  if (Boolean(strOrUndefined)) {
+      str = strOrUndefined;
+  }
+}
+
+
+//// [typeGuardBoolean.js]
+function test(strOrNull, strOrUndefined) {
+    var str = "original";
+    var nil;
+    if (!Boolean(strOrNull)) {
+        nil = strOrNull;
+    }
+    else {
+        str = strOrNull;
+    }
+    if (Boolean(strOrUndefined)) {
+        str = strOrUndefined;
+    }
+}
diff --git a/tests/baselines/reference/typeGuardBoolean.symbols b/tests/baselines/reference/typeGuardBoolean.symbols
new file mode 100644
index 0000000000000..6a08dcbda8a06
--- /dev/null
+++ b/tests/baselines/reference/typeGuardBoolean.symbols
@@ -0,0 +1,35 @@
+=== tests/cases/conformance/expressions/typeGuards/typeGuardBoolean.ts ===
+function test(strOrNull: string | null, strOrUndefined: string | undefined) {
+>test : Symbol(test, Decl(typeGuardBoolean.ts, 0, 0))
+>strOrNull : Symbol(strOrNull, Decl(typeGuardBoolean.ts, 0, 14))
+>strOrUndefined : Symbol(strOrUndefined, Decl(typeGuardBoolean.ts, 0, 39))
+
+  var str: string = "original";
+>str : Symbol(str, Decl(typeGuardBoolean.ts, 1, 5))
+
+  var nil: null;
+>nil : Symbol(nil, Decl(typeGuardBoolean.ts, 2, 5))
+
+  if (!Boolean(strOrNull)) {
+>Boolean : Symbol(Boolean, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>strOrNull : Symbol(strOrNull, Decl(typeGuardBoolean.ts, 0, 14))
+
+      nil = strOrNull;
+>nil : Symbol(nil, Decl(typeGuardBoolean.ts, 2, 5))
+>strOrNull : Symbol(strOrNull, Decl(typeGuardBoolean.ts, 0, 14))
+  }
+  else {
+      str = strOrNull;
+>str : Symbol(str, Decl(typeGuardBoolean.ts, 1, 5))
+>strOrNull : Symbol(strOrNull, Decl(typeGuardBoolean.ts, 0, 14))
+  }
+  if (Boolean(strOrUndefined)) {
+>Boolean : Symbol(Boolean, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>strOrUndefined : Symbol(strOrUndefined, Decl(typeGuardBoolean.ts, 0, 39))
+
+      str = strOrUndefined;
+>str : Symbol(str, Decl(typeGuardBoolean.ts, 1, 5))
+>strOrUndefined : Symbol(strOrUndefined, Decl(typeGuardBoolean.ts, 0, 39))
+  }
+}
+
diff --git a/tests/baselines/reference/typeGuardBoolean.types b/tests/baselines/reference/typeGuardBoolean.types
new file mode 100644
index 0000000000000..db3d6f39cd841
--- /dev/null
+++ b/tests/baselines/reference/typeGuardBoolean.types
@@ -0,0 +1,44 @@
+=== tests/cases/conformance/expressions/typeGuards/typeGuardBoolean.ts ===
+function test(strOrNull: string | null, strOrUndefined: string | undefined) {
+>test : (strOrNull: string | null, strOrUndefined: string | undefined) => void
+>strOrNull : string | null
+>null : null
+>strOrUndefined : string | undefined
+
+  var str: string = "original";
+>str : string
+>"original" : "original"
+
+  var nil: null;
+>nil : null
+>null : null
+
+  if (!Boolean(strOrNull)) {
+>!Boolean(strOrNull) : boolean
+>Boolean(strOrNull) : boolean
+>Boolean : BooleanConstructor
+>strOrNull : string | null
+
+      nil = strOrNull;
+>nil = strOrNull : null
+>nil : null
+>strOrNull : null
+  }
+  else {
+      str = strOrNull;
+>str = strOrNull : string
+>str : string
+>strOrNull : string
+  }
+  if (Boolean(strOrUndefined)) {
+>Boolean(strOrUndefined) : boolean
+>Boolean : BooleanConstructor
+>strOrUndefined : string | undefined
+
+      str = strOrUndefined;
+>str = strOrUndefined : string
+>str : string
+>strOrUndefined : string
+  }
+}
+