From 6f06fd0d466f24129088463c2226733749c06816 Mon Sep 17 00:00:00 2001
From: Daniel Rosenwasser <Daniel.Rosenwasser@microsoft.com>
Date: Thu, 28 Jun 2018 16:06:27 -0700
Subject: [PATCH] Use a more direct error.

---
 src/compiler/checker.ts                       | 33 +++++++++----------
 src/compiler/diagnosticMessages.json          |  2 +-
 .../unittests/tsserverProjectSystem.ts        |  6 ++--
 3 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index dfb10780fcb..1dc3c2cefba 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20904,31 +20904,30 @@ namespace ts {
             }
 
             function reportOperatorError() {
-                let err = chainDiagnosticMessages(
-                    /*elaboration*/ undefined,
-                    Diagnostics.Operator_0_cannot_be_applied_to_types_1_and_2,
-                    tokenToString(operatorToken.kind),
-                    typeToString(leftType),
-                    typeToString(rightType)
-                );
-                err = giveBetterPrimaryError(err);
-
-                diagnostics.add(createDiagnosticForNodeFromMessageChain(
-                    errorNode || operatorToken,
-                    err
-                ));
+                const leftStr = typeToString(leftType);
+                const rightStr = typeToString(rightType);
+                const errNode = errorNode || operatorToken;
+                if (!tryGiveBetterPrimaryError(errNode, leftStr, rightStr)) {
+                    error(
+                        errNode,
+                        Diagnostics.Operator_0_cannot_be_applied_to_types_1_and_2,
+                        tokenToString(operatorToken.kind),
+                        leftStr,
+                        rightStr,
+                    );
+                }
             }
 
-            function giveBetterPrimaryError(elaboration: DiagnosticMessageChain) {
+            function tryGiveBetterPrimaryError(errNode: Node, leftStr: string, rightStr: string) {
                 switch (operatorToken.kind) {
                     case SyntaxKind.EqualsEqualsEqualsToken:
                     case SyntaxKind.EqualsEqualsToken:
-                        return chainDiagnosticMessages(elaboration, Diagnostics.The_types_of_these_values_indicate_that_this_condition_will_always_be_0, "false");
+                        return error(errNode, Diagnostics.This_condition_will_always_return_0_since_the_types_1_and_2_have_no_overlap, "false", leftStr, rightStr);
                     case SyntaxKind.ExclamationEqualsEqualsToken:
                     case SyntaxKind.ExclamationEqualsToken:
-                        return chainDiagnosticMessages(elaboration, Diagnostics.The_types_of_these_values_indicate_that_this_condition_will_always_be_0, "true");
+                        return error(errNode, Diagnostics.This_condition_will_always_return_0_since_the_types_1_and_2_have_no_overlap, "true", leftStr, rightStr);
                     }
-                return elaboration;
+                return undefined;
             }
         }
 
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 5550cad86b7..d70db4d992b 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1252,7 +1252,7 @@
         "category": "Error",
         "code": 2366
     },
-    "The types of these values indicate that this condition will always be '{0}'.": {
+    "This condition will always return '{0}' since the types '{1}' and '{2}' have no overlap.": {
         "category": "Error",
         "code": 2367
     },
diff --git a/src/testRunner/unittests/tsserverProjectSystem.ts b/src/testRunner/unittests/tsserverProjectSystem.ts
index 860c7f8ef55..a917fd08d6d 100644
--- a/src/testRunner/unittests/tsserverProjectSystem.ts
+++ b/src/testRunner/unittests/tsserverProjectSystem.ts
@@ -5016,7 +5016,7 @@ namespace ts.projectSystem {
             );
             const errorResult = <protocol.Diagnostic[]>session.executeCommand(getErrRequest).response;
             assert.isTrue(errorResult.length === 1);
-            assert.equal(errorResult[0].code, Diagnostics.The_types_of_these_values_indicate_that_this_condition_will_always_be_0.code);
+            assert.equal(errorResult[0].code, Diagnostics.This_condition_will_always_return_0_since_the_types_1_and_2_have_no_overlap.code);
         });
 
         it("should report semantic errors for configured js project with '// @ts-check' and skipLibCheck=true", () => {
@@ -5043,7 +5043,7 @@ namespace ts.projectSystem {
             );
             const errorResult = <protocol.Diagnostic[]>session.executeCommand(getErrRequest).response;
             assert.isTrue(errorResult.length === 1);
-            assert.equal(errorResult[0].code, Diagnostics.The_types_of_these_values_indicate_that_this_condition_will_always_be_0.code);
+            assert.equal(errorResult[0].code, Diagnostics.This_condition_will_always_return_0_since_the_types_1_and_2_have_no_overlap.code);
         });
 
         it("should report semantic errors for configured js project with checkJs=true and skipLibCheck=true", () => {
@@ -5072,7 +5072,7 @@ namespace ts.projectSystem {
             );
             const errorResult = <protocol.Diagnostic[]>session.executeCommand(getErrRequest).response;
             assert.isTrue(errorResult.length === 1);
-            assert.equal(errorResult[0].code, Diagnostics.The_types_of_these_values_indicate_that_this_condition_will_always_be_0.code);
+            assert.equal(errorResult[0].code, Diagnostics.This_condition_will_always_return_0_since_the_types_1_and_2_have_no_overlap.code);
         });
     });