Improve error when an unresolved import matches a global namespace

tsc/internal/checker/checker.go

@@ -15422,6 +15422,25 @@ func (c *Checker) getCannotResolveModuleNameErrorForSpecificModule(moduleName *a
 	return nil
 }
 
+// Returns a more specific error when a failed non-relative module import matches a global
+// namespace declaration, e.g. `declare module foo { }`, which declares a namespace rather
+// than an ambient module. See https://github.com/microsoft/TypeScript/issues/23185.
+func (c *Checker) getCannotResolveModuleNameErrorForGlobalNamespace(moduleReference string) *diagnostics.Message {
+	if tspath.IsExternalModuleNameRelative(moduleReference) {
+		return nil
+	}
+	symbol := c.getGlobalSymbol(moduleReference, ast.SymbolFlagsModule, nil /*diagnostic*/)
+	if symbol == nil {
+		return nil
+	}
+	for _, declaration := range symbol.Declarations() {
+		if ast.IsModuleDeclaration(declaration) && !ast.IsStringLiteral(declaration.Name()) {
+			return diagnostics.Cannot_find_module_0_or_its_corresponding_type_declarations_Did_you_mean_to_use_the_global_namespace_0_If_you_meant_to_declare_an_ambient_module_the_name_must_be_quoted_Colon_declare_module_0
+		}
+	}
+	return nil
+}
+
 func (c *Checker) resolveExternalModuleNameWorker(location *ast.Node, moduleReferenceExpression *ast.Node, moduleNotFoundError *diagnostics.Message, ignoreErrors bool, isForAugmentation bool, importAttributesType *Type) *ast.Symbol {
 	if ast.IsStringLiteralLike(moduleReferenceExpression) {
 		if ast.IsSourcePhaseImport(moduleReferenceExpression.Parent) {
@@ -15716,6 +15735,11 @@ func (c *Checker) resolveExternalModule(
 	}
 
 	if moduleNotFoundError != nil {
+		if moduleNotFoundError == diagnostics.Cannot_find_module_0_or_its_corresponding_type_declarations {
+			if betterError := c.getCannotResolveModuleNameErrorForGlobalNamespace(moduleReference); betterError != nil {
+				moduleNotFoundError = betterError
+			}
+		}
 		// See if this was possibly a projectReference redirect
 		if resolvedModule.IsResolved() {
 			redirect := c.program.GetProjectReferenceFromSource(
@@ -15873,6 +15897,13 @@ func (c *Checker) errorOnImplicitAnyModule(isError bool, errorNode *ast.Node, mo
 		return
 	}
 
+	if isError {
+		if globalNamespaceError := c.getCannotResolveModuleNameErrorForGlobalNamespace(moduleReference); globalNamespaceError != nil {
+			c.error(errorNode, globalNamespaceError, moduleReference)
+			return
+		}
+	}
+
 	var errorInfo *ast.Diagnostic
 	if !tspath.IsExternalModuleNameRelative(moduleReference) && resolvedModule.PackageId.Name != "" {
 		errorInfo = c.createModuleNotFoundChain(resolvedModule, errorNode, moduleReference, mode, resolvedModule.PackageId.Name)

tsc/internal/diagnostics/diagnosticMessages.generated.json

@@ -1951,6 +1951,7 @@
     "Source_phase_imports_are_not_allowed_on_statements_that_compile_to_CommonJS_require_calls_18115": "Source phase imports are not allowed on statements that compile to CommonJS 'require' calls.",
     "This_initializer_has_a_Symbol_asyncDispose_method_Did_you_mean_to_use_await_using_18116": "This initializer has a '[Symbol.asyncDispose]()' method. Did you mean to use 'await using'?",
     "A_deferred_import_must_specify_a_namespace_binding_18117": "A deferred import must specify a namespace binding.",
+    "Cannot_find_module_0_or_its_corresponding_type_declarations_Did_you_mean_to_use_the_global_namespace_18118": "Cannot find module '{0}' or its corresponding type declarations. Did you mean to use the global namespace '{0}'? If you meant to declare an ambient module, the name must be quoted: `declare module '{0}';`.",
     "nodenext_if_module_is_nodenext_node16_if_module_is_node16_or_node18_otherwise_bundler_69010": "`nodenext` if `module` is `nodenext`; `node16` if `module` is `node16` or `node18`; otherwise, `bundler`.",
     "File_is_a_CommonJS_module_it_may_be_converted_to_an_ES_module_80001": "File is a CommonJS module; it may be converted to an ES module.",
     "This_constructor_function_may_be_converted_to_a_class_declaration_80002": "This constructor function may be converted to a class declaration.",

tsc/internal/diagnostics/diagnosticMessages.json

@@ -8923,5 +8923,9 @@
     "A deferred import must specify a namespace binding.": {
         "category": "Error",
         "code": 18117
+    },
+    "Cannot find module '{0}' or its corresponding type declarations. Did you mean to use the global namespace '{0}'? If you meant to declare an ambient module, the name must be quoted: `declare module '{0}';`.": {
+        "category": "Error",
+        "code": 18118
     }
 }

tsc/testdata/baselines/reference/compiler/cannotFindModuleWithGlobalNamespace.errors.txt

@@ -0,0 +1,41 @@
+globals.d.ts(1,16): error TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.
+globals.d.ts(4,16): error TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.
+main.ts(2,27): error TS18118: Cannot find module 'messageformat' or its corresponding type declarations. Did you mean to use the global namespace 'messageformat'? If you meant to declare an ambient module, the name must be quoted: `declare module 'messageformat';`.
+main.ts(3,19): error TS18118: Cannot find module 'otherlib' or its corresponding type declarations. Did you mean to use the global namespace 'otherlib'? If you meant to declare an ambient module, the name must be quoted: `declare module 'otherlib';`.
+main.ts(4,27): error TS2307: Cannot find module 'not-declared-globally' or its corresponding type declarations.
+
+
+==== main.ts (3 errors) ====
+    /// <reference path="globals.d.ts" />
+    import MessageFormat from "messageformat";
+                              ~~~~~~~~~~~~~~~
+!!! error TS18118: Cannot find module 'messageformat' or its corresponding type declarations. Did you mean to use the global namespace 'messageformat'? If you meant to declare an ambient module, the name must be quoted: `declare module 'messageformat';`.
+    import Other from "otherlib";
+                      ~~~~~~~~~~
+!!! error TS18118: Cannot find module 'otherlib' or its corresponding type declarations. Did you mean to use the global namespace 'otherlib'? If you meant to declare an ambient module, the name must be quoted: `declare module 'otherlib';`.
+    import { something } from "not-declared-globally";
+                              ~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2307: Cannot find module 'not-declared-globally' or its corresponding type declarations.
+
+==== /node_modules/messageformat/package.json (0 errors) ====
+    {
+        "name": "messageformat",
+        "version": "1.0.0",
+        "main": "lib/messageformat.js"
+    }
+
+==== /node_modules/messageformat/lib/messageformat.js (0 errors) ====
+    module.exports = function messageformat() {};
+
+==== globals.d.ts (2 errors) ====
+    declare module messageformat {
+                   ~~~~~~~~~~~~~
+!!! error TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.
+        export type Msg = (params: {}) => string;
+    }
+    declare module otherlib {
+                   ~~~~~~~~
+!!! error TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.
+        export type Other = string;
+    }
+

tsc/testdata/baselines/reference/compiler/cannotFindModuleWithGlobalNamespace.js

@@ -0,0 +1,29 @@
+//// [tests/cases/compiler/cannotFindModuleWithGlobalNamespace.ts] ////
+
+//// [package.json]
+{
+    "name": "messageformat",
+    "version": "1.0.0",
+    "main": "lib/messageformat.js"
+}
+
+//// [messageformat.js]
+module.exports = function messageformat() {};
+
+//// [globals.d.ts]
+declare module messageformat {
+    export type Msg = (params: {}) => string;
+}
+declare module otherlib {
+    export type Other = string;
+}
+
+//// [main.ts]
+/// <reference path="globals.d.ts" />
+import MessageFormat from "messageformat";
+import Other from "otherlib";
+import { something } from "not-declared-globally";
+
+
+//// [main.js]
+export {};

tsc/testdata/baselines/reference/compiler/cannotFindModuleWithGlobalNamespace.symbols

@@ -0,0 +1,28 @@
+//// [tests/cases/compiler/cannotFindModuleWithGlobalNamespace.ts] ////
+
+=== main.ts ===
+/// <reference path="globals.d.ts" />
+import MessageFormat from "messageformat";
+>MessageFormat : Symbol(MessageFormat, Decl(main.ts, 1, 6))
+
+import Other from "otherlib";
+>Other : Symbol(Other, Decl(main.ts, 2, 6))
+
+import { something } from "not-declared-globally";
+>something : Symbol(something, Decl(main.ts, 3, 8))
+
+=== globals.d.ts ===
+declare module messageformat {
+>messageformat : Symbol(messageformat, Decl(globals.d.ts, 0, 0))
+
+    export type Msg = (params: {}) => string;
+>Msg : Symbol(Msg, Decl(globals.d.ts, 0, 30))
+>params : Symbol(params, Decl(globals.d.ts, 1, 23))
+}
+declare module otherlib {
+>otherlib : Symbol(otherlib, Decl(globals.d.ts, 2, 1))
+
+    export type Other = string;
+>Other : Symbol(Other, Decl(globals.d.ts, 3, 25))
+}
+

tsc/testdata/baselines/reference/compiler/cannotFindModuleWithGlobalNamespace.types

@@ -0,0 +1,24 @@
+//// [tests/cases/compiler/cannotFindModuleWithGlobalNamespace.ts] ////
+
+=== main.ts ===
+/// <reference path="globals.d.ts" />
+import MessageFormat from "messageformat";
+>MessageFormat : any
+
+import Other from "otherlib";
+>Other : any
+
+import { something } from "not-declared-globally";
+>something : any
+
+=== globals.d.ts ===
+declare module messageformat {
+    export type Msg = (params: {}) => string;
+>Msg : Msg
+>params : {}
+}
+declare module otherlib {
+    export type Other = string;
+>Other : string
+}
+

tsc/testdata/tests/cases/compiler/cannotFindModuleWithGlobalNamespace.ts

@@ -0,0 +1,26 @@
+// @strict: true
+// @noImplicitReferences: true
+
+// @Filename: /node_modules/messageformat/package.json
+{
+    "name": "messageformat",
+    "version": "1.0.0",
+    "main": "lib/messageformat.js"
+}
+
+// @Filename: /node_modules/messageformat/lib/messageformat.js
+module.exports = function messageformat() {};
+
+// @Filename: globals.d.ts
+declare module messageformat {
+    export type Msg = (params: {}) => string;
+}
+declare module otherlib {
+    export type Other = string;
+}
+
+// @Filename: main.ts
+/// <reference path="globals.d.ts" />
+import MessageFormat from "messageformat";
+import Other from "otherlib";
+import { something } from "not-declared-globally";