Adds an --experimentalThrowExpressions flag

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;
         }

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
         {

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

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;

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();

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();