Report CommonJS top-level Object value collisions in checker (#3870)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>

Author: Copilot

internal/checker/checker.go

@@ -10402,6 +10402,7 @@ func (c *Checker) checkCollisionsForDeclarationName(node *ast.Node, name *ast.No
 		return
 	}
 	c.checkCollisionWithRequireExportsInGeneratedCode(node, name)
+	c.checkCollisionWithGlobalObjectInGeneratedCode(node, name)
 	c.checkCollisionWithGlobalPromiseInGeneratedCode(node, name)
 	c.recordPotentialCollisionWithWeakMapSetInGeneratedCode(node, name)
 	c.recordPotentialCollisionWithReflectInGeneratedCode(node, name)
@@ -10435,6 +10436,22 @@ func (c *Checker) checkCollisionWithRequireExportsInGeneratedCode(node *ast.Node
 	}
 }
 
+func (c *Checker) checkCollisionWithGlobalObjectInGeneratedCode(node *ast.Node, name *ast.Node) {
+	if name == nil || ast.IsClassLike(node) || !c.needCollisionCheckForIdentifier(node, name, "Object") {
+		return
+	}
+	// Uninstantiated modules shouldn't do this check
+	if ast.IsModuleDeclaration(node) && ast.GetModuleInstanceState(node) != ast.ModuleInstanceStateInstantiated {
+		return
+	}
+	// In case of variable declaration, node.parent is variable statement so look at the variable statement's parent
+	parent := ast.GetDeclarationContainer(node)
+	if ast.IsSourceFile(parent) && ast.IsExternalOrCommonJSModule(parent.AsSourceFile()) && c.program.GetEmitModuleFormatOfFile(parent.AsSourceFile()) == core.ModuleKindCommonJS {
+		// If the declaration happens to be in external module, report error that Object is a reserved identifier.
+		c.errorSkippedOnNoEmit(name, diagnostics.Duplicate_identifier_0_Compiler_reserves_name_1_in_top_level_scope_of_a_module, scanner.DeclarationNameToString(name), scanner.DeclarationNameToString(name))
+	}
+}
+
 func (c *Checker) needCollisionCheckForIdentifier(node *ast.Node, identifier *ast.Node, name string) bool {
 	if identifier != nil && identifier.Text() != name {
 		return false

testdata/baselines/reference/compiler/objectNameCollisionCommonJS(module=commonjs).errors.txt

@@ -0,0 +1,9 @@
+objectNameCollisionCommonJS.ts(1,5): error TS2441: Duplicate identifier 'Object'. Compiler reserves name 'Object' in top level scope of a module.
+
+
+==== objectNameCollisionCommonJS.ts (1 errors) ====
+    let Object = 0;
+        ~~~~~~
+!!! error TS2441: Duplicate identifier 'Object'. Compiler reserves name 'Object' in top level scope of a module.
+    export const x = 1;
+    

testdata/baselines/reference/compiler/objectNameCollisionCommonJS(module=commonjs).js

@@ -0,0 +1,13 @@
+//// [tests/cases/compiler/objectNameCollisionCommonJS.ts] ////
+
+//// [objectNameCollisionCommonJS.ts]
+let Object = 0;
+export const x = 1;
+
+
+//// [objectNameCollisionCommonJS.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.x = void 0;
+let Object = 0;
+exports.x = 1;

testdata/baselines/reference/compiler/objectNameCollisionCommonJS(module=commonjs).symbols

@@ -0,0 +1,9 @@
+//// [tests/cases/compiler/objectNameCollisionCommonJS.ts] ////
+
+=== objectNameCollisionCommonJS.ts ===
+let Object = 0;
+>Object : Symbol(Object, Decl(objectNameCollisionCommonJS.ts, 0, 3))
+
+export const x = 1;
+>x : Symbol(x, Decl(objectNameCollisionCommonJS.ts, 1, 12))
+

testdata/baselines/reference/compiler/objectNameCollisionCommonJS(module=commonjs).types

@@ -0,0 +1,11 @@
+//// [tests/cases/compiler/objectNameCollisionCommonJS.ts] ////
+
+=== objectNameCollisionCommonJS.ts ===
+let Object = 0;
+>Object : number
+>0 : 0
+
+export const x = 1;
+>x : 1
+>1 : 1
+

testdata/baselines/reference/compiler/objectNameCollisionCommonJS(module=esnext).js

@@ -0,0 +1,10 @@
+//// [tests/cases/compiler/objectNameCollisionCommonJS.ts] ////
+
+//// [objectNameCollisionCommonJS.ts]
+let Object = 0;
+export const x = 1;
+
+
+//// [objectNameCollisionCommonJS.js]
+let Object = 0;
+export const x = 1;

testdata/baselines/reference/compiler/objectNameCollisionCommonJS(module=esnext).symbols

@@ -0,0 +1,9 @@
+//// [tests/cases/compiler/objectNameCollisionCommonJS.ts] ////
+
+=== objectNameCollisionCommonJS.ts ===
+let Object = 0;
+>Object : Symbol(Object, Decl(objectNameCollisionCommonJS.ts, 0, 3))
+
+export const x = 1;
+>x : Symbol(x, Decl(objectNameCollisionCommonJS.ts, 1, 12))
+

testdata/baselines/reference/compiler/objectNameCollisionCommonJS(module=esnext).types

@@ -0,0 +1,11 @@
+//// [tests/cases/compiler/objectNameCollisionCommonJS.ts] ////
+
+=== objectNameCollisionCommonJS.ts ===
+let Object = 0;
+>Object : number
+>0 : 0
+
+export const x = 1;
+>x : 1
+>1 : 1
+

testdata/tests/cases/compiler/objectNameCollisionCommonJS.ts

@@ -0,0 +1,4 @@
+// @module: commonjs,esnext
+
+let Object = 0;
+export const x = 1;