Even better "always true/false" errors

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;
             }
         }
 

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
     },

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);
         });
     });
 

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -5152,7 +5152,7 @@ declare namespace ts {
         The_left_hand_side_of_an_assignment_expression_must_be_a_variable_or_a_property_access: DiagnosticMessage;
         Operator_0_cannot_be_applied_to_types_1_and_2: DiagnosticMessage;
         Function_lacks_ending_return_statement_and_return_type_does_not_include_undefined: DiagnosticMessage;
-        The_types_of_these_values_indicate_that_this_condition_will_always_be_0: DiagnosticMessage;
+        This_condition_will_always_return_0_since_the_types_1_and_2_have_no_overlap: DiagnosticMessage;
         Type_parameter_name_cannot_be_0: DiagnosticMessage;
         A_parameter_property_is_only_allowed_in_a_constructor_implementation: DiagnosticMessage;
         A_rest_parameter_must_be_of_an_array_type: DiagnosticMessage;

tests/baselines/reference/capturedLetConstInLoop5.errors.txt

@@ -1,7 +1,5 @@
-tests/cases/compiler/capturedLetConstInLoop5.ts(174,13): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '1'.
-tests/cases/compiler/capturedLetConstInLoop5.ts(229,13): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '1'.
+tests/cases/compiler/capturedLetConstInLoop5.ts(174,13): error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
+tests/cases/compiler/capturedLetConstInLoop5.ts(229,13): error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
 
 
 ==== tests/cases/compiler/capturedLetConstInLoop5.ts (2 errors) ====
@@ -180,8 +178,7 @@ tests/cases/compiler/capturedLetConstInLoop5.ts(229,13): error TS2367: The types
             (() => x + v);
             if (x == 1) {
                 ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '1'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
                 return;
             }
         }
@@ -238,8 +235,7 @@ tests/cases/compiler/capturedLetConstInLoop5.ts(229,13): error TS2367: The types
             (() => x + y + v);
             if (x == 1) {
                 ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '1'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
                 return;
             }
         }

tests/baselines/reference/capturedLetConstInLoop5_ES6.errors.txt

@@ -1,7 +1,5 @@
-tests/cases/compiler/capturedLetConstInLoop5_ES6.ts(174,13): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '1'.
-tests/cases/compiler/capturedLetConstInLoop5_ES6.ts(229,13): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '1'.
+tests/cases/compiler/capturedLetConstInLoop5_ES6.ts(174,13): error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
+tests/cases/compiler/capturedLetConstInLoop5_ES6.ts(229,13): error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
 
 
 ==== tests/cases/compiler/capturedLetConstInLoop5_ES6.ts (2 errors) ====
@@ -180,8 +178,7 @@ tests/cases/compiler/capturedLetConstInLoop5_ES6.ts(229,13): error TS2367: The t
             (() => x + v);
             if (x == 1) {
                 ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '1'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
                 return;
             }
         }
@@ -238,8 +235,7 @@ tests/cases/compiler/capturedLetConstInLoop5_ES6.ts(229,13): error TS2367: The t
             (() => x + y + v);
             if (x == 1) {
                 ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '1'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
                 return;
             }
         }

tests/baselines/reference/capturedLetConstInLoop6.errors.txt

@@ -1,11 +1,7 @@
-tests/cases/compiler/capturedLetConstInLoop6.ts(147,9): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '1'.
-tests/cases/compiler/capturedLetConstInLoop6.ts(150,9): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '2'.
-tests/cases/compiler/capturedLetConstInLoop6.ts(194,9): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '1'.
-tests/cases/compiler/capturedLetConstInLoop6.ts(197,9): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '2'.
+tests/cases/compiler/capturedLetConstInLoop6.ts(147,9): error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
+tests/cases/compiler/capturedLetConstInLoop6.ts(150,9): error TS2367: This condition will always return 'false' since the types '0' and '2' have no overlap.
+tests/cases/compiler/capturedLetConstInLoop6.ts(194,9): error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
+tests/cases/compiler/capturedLetConstInLoop6.ts(197,9): error TS2367: This condition will always return 'false' since the types '0' and '2' have no overlap.
 
 
 ==== tests/cases/compiler/capturedLetConstInLoop6.ts (4 errors) ====
@@ -157,14 +153,12 @@ tests/cases/compiler/capturedLetConstInLoop6.ts(197,9): error TS2367: The types
         (() => x);
         if (x == 1) {
             ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '1'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
             break;
         }
         if (x == 2) {
             ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '2'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '2' have no overlap.
             continue;
         }
     }
@@ -210,14 +204,12 @@ tests/cases/compiler/capturedLetConstInLoop6.ts(197,9): error TS2367: The types
         (() => x + y);
         if (x == 1) {
             ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '1'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
             break;
         }
         if (x == 2) {
             ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '2'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '2' have no overlap.
             continue;
         }
     }

tests/baselines/reference/capturedLetConstInLoop6_ES6.errors.txt

@@ -1,11 +1,7 @@
-tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(147,9): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '1'.
-tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(150,9): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '2'.
-tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(194,9): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '1'.
-tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(197,9): error TS2367: The types of these values indicate that this condition will always be 'false'.
-  Operator '==' cannot be applied to types '0' and '2'.
+tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(147,9): error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
+tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(150,9): error TS2367: This condition will always return 'false' since the types '0' and '2' have no overlap.
+tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(194,9): error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
+tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(197,9): error TS2367: This condition will always return 'false' since the types '0' and '2' have no overlap.
 
 
 ==== tests/cases/compiler/capturedLetConstInLoop6_ES6.ts (4 errors) ====
@@ -157,14 +153,12 @@ tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(197,9): error TS2367: The ty
         (() => x);
         if (x == 1) {
             ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '1'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
             break;
         }
         if (x == 2) {
             ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '2'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '2' have no overlap.
             continue;
         }
     }
@@ -210,14 +204,12 @@ tests/cases/compiler/capturedLetConstInLoop6_ES6.ts(197,9): error TS2367: The ty
         (() => x + y);
         if (x == 1) {
             ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '1'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '1' have no overlap.
             break;
         }
         if (x == 2) {
             ~~~~~~
-!!! error TS2367: The types of these values indicate that this condition will always be 'false'.
-!!! error TS2367:   Operator '==' cannot be applied to types '0' and '2'.
+!!! error TS2367: This condition will always return 'false' since the types '0' and '2' have no overlap.
             continue;
         }
     }