isolatedModules error on global shadowed by imported type

src/compiler/checker.ts

@@ -735,6 +735,7 @@ import {
     isTypeNode,
     isTypeNodeKind,
     isTypeOfExpression,
+    isTypeOnlyImportDeclaration,
     isTypeOnlyImportOrExportDeclaration,
     isTypeOperatorNode,
     isTypeParameterDeclaration,
@@ -3603,6 +3604,19 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                         );
                     }
                 }
+
+                // Look at 'compilerOptions.isolatedModules' and not 'getIsolatedModules(...)' (which considers 'verbatimModuleSyntax')
+                // here because 'verbatimModuleSyntax' will already have an error for importing a type without 'import type'.
+                if (compilerOptions.isolatedModules && result && isInExternalModule && (meaning & SymbolFlags.Value) === SymbolFlags.Value) {
+                    const isGlobal = lookup(globals, name, meaning) === result;
+                    const nonValueSymbol = isGlobal && isSourceFile(lastLocation!) && lastLocation.locals && lookup(lastLocation.locals, name, ~SymbolFlags.Value);
+                    if (nonValueSymbol) {
+                        const importDecl = nonValueSymbol.declarations?.find(d => d.kind === SyntaxKind.ImportSpecifier || d.kind === SyntaxKind.ImportClause || d.kind === SyntaxKind.NamespaceImport || d.kind === SyntaxKind.ImportEqualsDeclaration);
+                        if (importDecl && !isTypeOnlyImportDeclaration(importDecl)) {
+                            error(importDecl, Diagnostics.Import_0_conflicts_with_global_value_used_in_this_file_so_must_be_declared_with_a_type_only_import_when_isolatedModules_is_enabled, unescapeLeadingUnderscores(name));
+                        }
+                    }
+                }
             });
         }
         return result;

src/compiler/diagnosticMessages.json

@@ -3731,6 +3731,10 @@
         "category": "Error",
         "code": 2865
     },
+    "Import '{0}' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.": {
+        "category": "Error",
+        "code": 2866
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

tests/baselines/reference/isolatedModulesShadowGlobalTypeNotValue(isolatedmodules=false,verbatimmodulesyntax=true).errors.txt

@@ -0,0 +1,67 @@
+bad.ts(1,10): error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+bad.ts(1,10): error TS1484: 'Date' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.
+bad.ts(1,16): error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+bad.ts(1,16): error TS1484: 'Event' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.
+good.ts(2,10): error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+
+
+==== ./types.ts (0 errors) ====
+    export interface Date {
+        day: number;
+        month: number;
+        year: number;
+    }
+
+    export namespace Event {
+        export type T = any;
+    }
+
+==== ./node.d.ts (0 errors) ====
+    declare module 'node:console' {
+        global {
+            interface Console {
+                Console: console.ConsoleConstructor;
+            }
+            namespace console {
+                interface ConsoleConstructor {
+                    prototype: Console;
+                    new (): Console;
+                }
+            }
+            var console: Console;
+        }
+        export = globalThis.console;
+    }
+
+==== ./bad.ts (4 errors) ====
+    import { Date, Event } from './types';
+             ~~~~
+!!! error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+             ~~~~
+!!! error TS1484: 'Date' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.
+                   ~~~~~
+!!! error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+                   ~~~~~
+!!! error TS1484: 'Event' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.
+    function foo(a: Date) {
+        const b = new Date(a.year, a.month, a.day);
+        return b.getTime();
+    }
+    function bar() {
+        return new Event('bar') as Event.T;
+    }
+
+==== ./good.ts (1 errors) ====
+    import type { Date, Event } from './types';
+    import { Console } from 'node:console';
+             ~~~~~~~
+!!! error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+    function foo(a: Date) {
+        const b = new Date(a.year, a.month, a.day);
+        return b.getTime();
+    }
+    function bar() {
+        return new Event('bar') as Event.T;
+    }
+    const baz: Console = new Console();
+

tests/baselines/reference/isolatedModulesShadowGlobalTypeNotValue(isolatedmodules=true,verbatimmodulesyntax=false).errors.txt

@@ -0,0 +1,58 @@
+bad.ts(1,10): error TS2866: Import 'Date' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.
+bad.ts(1,16): error TS2866: Import 'Event' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.
+
+
+==== ./types.ts (0 errors) ====
+    export interface Date {
+        day: number;
+        month: number;
+        year: number;
+    }
+
+    export namespace Event {
+        export type T = any;
+    }
+
+==== ./node.d.ts (0 errors) ====
+    declare module 'node:console' {
+        global {
+            interface Console {
+                Console: console.ConsoleConstructor;
+            }
+            namespace console {
+                interface ConsoleConstructor {
+                    prototype: Console;
+                    new (): Console;
+                }
+            }
+            var console: Console;
+        }
+        export = globalThis.console;
+    }
+
+==== ./bad.ts (2 errors) ====
+    import { Date, Event } from './types';
+             ~~~~
+!!! error TS2866: Import 'Date' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.
+                   ~~~~~
+!!! error TS2866: Import 'Event' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.
+    function foo(a: Date) {
+        const b = new Date(a.year, a.month, a.day);
+        return b.getTime();
+    }
+    function bar() {
+        return new Event('bar') as Event.T;
+    }
+
+==== ./good.ts (0 errors) ====
+    import type { Date, Event } from './types';
+    import { Console } from 'node:console';
+    function foo(a: Date) {
+        const b = new Date(a.year, a.month, a.day);
+        return b.getTime();
+    }
+    function bar() {
+        return new Event('bar') as Event.T;
+    }
+    const baz: Console = new Console();
+

tests/baselines/reference/isolatedModulesShadowGlobalTypeNotValue(isolatedmodules=true,verbatimmodulesyntax=true).errors.txt

@@ -0,0 +1,73 @@
+bad.ts(1,10): error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+bad.ts(1,10): error TS1484: 'Date' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.
+bad.ts(1,10): error TS2866: Import 'Date' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.
+bad.ts(1,16): error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+bad.ts(1,16): error TS1484: 'Event' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.
+bad.ts(1,16): error TS2866: Import 'Event' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.
+good.ts(2,10): error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+
+
+==== ./types.ts (0 errors) ====
+    export interface Date {
+        day: number;
+        month: number;
+        year: number;
+    }
+
+    export namespace Event {
+        export type T = any;
+    }
+
+==== ./node.d.ts (0 errors) ====
+    declare module 'node:console' {
+        global {
+            interface Console {
+                Console: console.ConsoleConstructor;
+            }
+            namespace console {
+                interface ConsoleConstructor {
+                    prototype: Console;
+                    new (): Console;
+                }
+            }
+            var console: Console;
+        }
+        export = globalThis.console;
+    }
+
+==== ./bad.ts (6 errors) ====
+    import { Date, Event } from './types';
+             ~~~~
+!!! error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+             ~~~~
+!!! error TS1484: 'Date' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.
+             ~~~~
+!!! error TS2866: Import 'Date' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.
+                   ~~~~~
+!!! error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+                   ~~~~~
+!!! error TS1484: 'Event' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.
+                   ~~~~~
+!!! error TS2866: Import 'Event' conflicts with global value used in this file, so must be declared with a type-only import when 'isolatedModules' is enabled.
+    function foo(a: Date) {
+        const b = new Date(a.year, a.month, a.day);
+        return b.getTime();
+    }
+    function bar() {
+        return new Event('bar') as Event.T;
+    }
+
+==== ./good.ts (1 errors) ====
+    import type { Date, Event } from './types';
+    import { Console } from 'node:console';
+             ~~~~~~~
+!!! error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.
+    function foo(a: Date) {
+        const b = new Date(a.year, a.month, a.day);
+        return b.getTime();
+    }
+    function bar() {
+        return new Event('bar') as Event.T;
+    }
+    const baz: Console = new Console();
+

tests/cases/compiler/isolatedModulesShadowGlobalTypeNotValue.ts

@@ -0,0 +1,54 @@
+// @isolatedModules: false, true
+// @verbatimModuleSyntax: false, true
+// @noEmit: true
+// @noTypesAndSymbols: true
+
+// @filename: ./types.ts
+export interface Date {
+    day: number;
+    month: number;
+    year: number;
+}
+
+export namespace Event {
+    export type T = any;
+}
+
+// @filename: ./node.d.ts
+declare module 'node:console' {
+    global {
+        interface Console {
+            Console: console.ConsoleConstructor;
+        }
+        namespace console {
+            interface ConsoleConstructor {
+                prototype: Console;
+                new (): Console;
+            }
+        }
+        var console: Console;
+    }
+    export = globalThis.console;
+}
+
+// @filename: ./bad.ts
+import { Date, Event } from './types';
+function foo(a: Date) {
+    const b = new Date(a.year, a.month, a.day);
+    return b.getTime();
+}
+function bar() {
+    return new Event('bar') as Event.T;
+}
+
+// @filename: ./good.ts
+import type { Date, Event } from './types';
+import { Console } from 'node:console';
+function foo(a: Date) {
+    const b = new Date(a.year, a.month, a.day);
+    return b.getTime();
+}
+function bar() {
+    return new Event('bar') as Event.T;
+}
+const baz: Console = new Console();