From 3a96b18910c0d54a26fa42c41bcadca20a30591a Mon Sep 17 00:00:00 2001
From: Ron Buckton <ron.buckton@microsoft.com>
Date: Wed, 27 Sep 2017 14:22:11 -0400
Subject: [PATCH] Adds an --experimentalThrowExpressions flag

---
 src/compiler/checker.ts                                  | 4 ++++
 src/compiler/commandLineParser.ts                        | 6 ++++++
 src/compiler/diagnosticMessages.json                     | 9 +++++++++
 src/compiler/types.ts                                    | 1 +
 .../throwExpressions/throwExpressions.es2015.ts          | 1 +
 .../throwExpressions/throwExpressions.esnext.ts          | 1 +
 6 files changed, 22 insertions(+)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index db8b0a542e5..7430faa7197 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -17179,6 +17179,10 @@ namespace ts {
         }
 
         function checkThrowExpression(node: ThrowExpression): Type {
+            if (!compilerOptions.experimentalThrowExpressions) {
+                error(node, Diagnostics.Experimental_support_for_throw_expressions_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalThrowExpressions_option_to_remove_this_warning);
+            }
+
             checkExpression(node.expression);
             return neverType;
         }
diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 54e5ee1d01d..c7f8d141d06 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -433,6 +433,12 @@ namespace ts {
             category: Diagnostics.Experimental_Options,
             description: Diagnostics.Enables_experimental_support_for_emitting_type_metadata_for_decorators
         },
+        {
+            name: "experimentalThrowExpressions",
+            type: "boolean",
+            category: Diagnostics.Experimental_Options,
+            description: Diagnostics.Enables_experimental_support_for_ECMAScript_Stage_2_throw_expressions
+        },
 
         // Advanced
         {
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 9c0b549da50..d23348c3bd0 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -907,6 +907,10 @@
         "category": "Error",
         "code": 1328
     },
+    "Experimental support for 'throw' expressions is a feature that is subject to change in a future release. Set the 'experimentalThrowExpressions' option to remove this warning.": {
+        "category": "Error",
+        "code": 1329
+    },
 
     "Duplicate identifier '{0}'.": {
         "category": "Error",
@@ -3314,6 +3318,11 @@
         "category": "Message",
         "code": 6185
     },
+    "Enables experimental support for ECMAScript Stage-2 'throw' expressions.": {
+        "category": "Message",
+        "code": 6186
+    },
+
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
         "code": 7005
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 48241efb04a..6d9dbaa0764 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -3658,6 +3658,7 @@ namespace ts {
         emitBOM?: boolean;
         emitDecoratorMetadata?: boolean;
         experimentalDecorators?: boolean;
+        experimentalThrowExpressions?: boolean;
         forceConsistentCasingInFileNames?: boolean;
         /*@internal*/help?: boolean;
         importHelpers?: boolean;
diff --git a/tests/cases/conformance/expressions/throwExpressions/throwExpressions.es2015.ts b/tests/cases/conformance/expressions/throwExpressions/throwExpressions.es2015.ts
index fc665db0b03..4a25d78965d 100644
--- a/tests/cases/conformance/expressions/throwExpressions/throwExpressions.es2015.ts
+++ b/tests/cases/conformance/expressions/throwExpressions/throwExpressions.es2015.ts
@@ -1,4 +1,5 @@
 // @target: es2015
+// @experimentalThrowExpressions: true
 declare const condition: boolean;
 const a = condition ? 1 : throw new Error();
 const b = condition || throw new Error();
diff --git a/tests/cases/conformance/expressions/throwExpressions/throwExpressions.esnext.ts b/tests/cases/conformance/expressions/throwExpressions/throwExpressions.esnext.ts
index 2a41f11e19f..f34f6ff85a4 100644
--- a/tests/cases/conformance/expressions/throwExpressions/throwExpressions.esnext.ts
+++ b/tests/cases/conformance/expressions/throwExpressions/throwExpressions.esnext.ts
@@ -1,4 +1,5 @@
 // @target: esnext
+// @experimentalThrowExpressions: true
 declare const condition: boolean;
 const a = condition ? 1 : throw new Error();
 const b = condition || throw new Error();