chore: add TS2839 to JS files

chore: add test files

chore: update tests

Author: Jack-Works

src/compiler/checker.ts

@@ -37029,8 +37029,13 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 // types may cause the operands to not be comparable. We don't want such errors reported (see #46475).
                 if (!(checkMode && checkMode & CheckMode.TypeOnly)) {
                     if (isLiteralExpressionOfObject(left) || isLiteralExpressionOfObject(right)) {
-                        const eqType = operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.EqualsEqualsEqualsToken;
-                        error(errorNode, Diagnostics.This_condition_will_always_return_0_since_JavaScript_compares_objects_by_reference_not_value, eqType ? "false" : "true");
+                        if (isInJSFile(left) && (operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.ExclamationEqualsToken)) {
+                            // we skip the emit for {} == {} in JS files
+                        }
+                        else {
+                            const eqType = operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.EqualsEqualsEqualsToken;
+                            error(errorNode, Diagnostics.This_condition_will_always_return_0_since_JavaScript_compares_objects_by_reference_not_value, eqType ? "false" : "true");
+                        }
                     }
                     checkNaNEquality(errorNode, operator, left, right);
                     reportOperatorErrorUnless((left, right) => isTypeEqualityComparableTo(left, right) || isTypeEqualityComparableTo(right, left));

src/compiler/program.ts

@@ -1430,6 +1430,8 @@ export const plainJSErrors: Set<number> = new Set([
     Diagnostics.Class_constructor_may_not_be_a_generator.code,
     Diagnostics.Class_constructor_may_not_be_an_accessor.code,
     Diagnostics.await_expressions_are_only_allowed_within_async_functions_and_at_the_top_levels_of_modules.code,
+    // Type errors
+    Diagnostics.This_condition_will_always_return_0_since_JavaScript_compares_objects_by_reference_not_value.code,
 ]);
 
 /**

tests/baselines/reference/plainJSTypeErrors.errors.txt

@@ -0,0 +1,12 @@
+tests/cases/conformance/salsa/plainJSTypeErrors.js(2,5): error TS2839: This condition will always return 'false' since JavaScript compares objects by reference, not value.
+
+
+==== tests/cases/conformance/salsa/plainJSTypeErrors.js (1 errors) ====
+    // should error
+    if ({} === {}) {}
+        ~~~~~~~~~
+!!! error TS2839: This condition will always return 'false' since JavaScript compares objects by reference, not value.
+    
+    // should not error
+    if ({} == {}) {}
+    

tests/baselines/reference/plainJSTypeErrors.js

@@ -0,0 +1,13 @@
+//// [plainJSTypeErrors.js]
+// should error
+if ({} === {}) {}
+
+// should not error
+if ({} == {}) {}
+
+
+//// [plainJSTypeErrors.js]
+// should error
+if ({} === {}) { }
+// should not error
+if ({} == {}) { }

tests/baselines/reference/plainJSTypeErrors.symbols

@@ -0,0 +1,8 @@
+=== tests/cases/conformance/salsa/plainJSTypeErrors.js ===
+// should error
+No type information for this code.if ({} === {}) {}
+No type information for this code.
+No type information for this code.// should not error
+No type information for this code.if ({} == {}) {}
+No type information for this code.
+No type information for this code.

tests/baselines/reference/plainJSTypeErrors.types

@@ -0,0 +1,13 @@
+=== tests/cases/conformance/salsa/plainJSTypeErrors.js ===
+// should error
+if ({} === {}) {}
+>{} === {} : boolean
+>{} : {}
+>{} : {}
+
+// should not error
+if ({} == {}) {}
+>{} == {} : boolean
+>{} : {}
+>{} : {}
+

tests/cases/conformance/salsa/plainJSTypeErrors.ts

@@ -0,0 +1,10 @@
+// @outdir: out/
+// @target: esnext
+// @allowJS: true
+// @filename: plainJSTypeErrors.js
+
+// should error
+if ({} === {}) {}
+
+// should not error
+if ({} == {}) {}