Add support for import.defer(...)

src/compiler/checker.ts

@@ -37650,7 +37650,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             error(node, Diagnostics.The_import_meta_meta_property_is_only_allowed_when_the_module_option_is_es2020_es2022_esnext_system_node16_node18_or_nodenext);
         }
         const file = getSourceFileOfNode(node);
-        Debug.assert(!!(file.flags & NodeFlags.PossiblyContainsImportMeta), "Containing file is missing import meta node flag.");
+        Debug.assert(node.name.escapedText === "defer" || !!(file.flags & NodeFlags.PossiblyContainsImportMeta), "Containing file is missing import meta node flag.");
         return node.name.escapedText === "meta" ? getGlobalImportMetaType() : errorType;
     }
 
@@ -41172,8 +41172,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             case SyntaxKind.ElementAccessExpression:
                 return checkIndexedAccess(node as ElementAccessExpression, checkMode);
             case SyntaxKind.CallExpression:
-                if ((node as CallExpression).expression.kind === SyntaxKind.ImportKeyword) {
-                    return checkImportCallExpression(node as ImportCall);
+                if (isImportCall(node)) {
+                    return checkImportCallExpression(node);
                 }
                 // falls through
             case SyntaxKind.NewExpression:
@@ -52612,8 +52612,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 }
                 break;
             case SyntaxKind.ImportKeyword:
-                if (escapedText !== "meta") {
-                    return grammarErrorOnNode(node.name, Diagnostics._0_is_not_a_valid_meta_property_for_keyword_1_Did_you_mean_2, unescapeLeadingUnderscores(node.name.escapedText), tokenToString(node.keywordToken), "meta");
+                if (escapedText !== "meta" && escapedText !== "defer") {
+                    const suggestion = node.parent.kind === SyntaxKind.CallExpression && (node.parent as CallExpression).expression === node
+                        ? "meta' or 'defer"
+                        : "meta";
+                    return grammarErrorOnNode(node.name, Diagnostics._0_is_not_a_valid_meta_property_for_keyword_1_Did_you_mean_2, unescapeLeadingUnderscores(node.name.escapedText), tokenToString(node.keywordToken), suggestion);
                 }
                 break;
         }
@@ -52902,6 +52905,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return grammarErrorOnNode(node, Diagnostics.ESM_syntax_is_not_allowed_in_a_CommonJS_module_when_verbatimModuleSyntax_is_enabled);
         }
 
+        if (node.expression.kind === SyntaxKind.MetaProperty) {
+            if (moduleKind !== ModuleKind.ESNext) {
+                return grammarErrorOnNode(node, Diagnostics.Deferred_imports_are_only_supported_when_the_module_flag_is_set_to_esnext);
+            }
+        }
         if (moduleKind === ModuleKind.ES2015) {
             return grammarErrorOnNode(node, Diagnostics.Dynamic_imports_are_only_supported_when_the_module_flag_is_set_to_es2020_es2022_esnext_commonjs_amd_system_umd_node16_node18_or_nodenext);
         }

src/compiler/diagnosticMessages.json

@@ -8445,5 +8445,9 @@
     "Deferred imports are only supported when the '--module' flag is set to 'esnext'.": {
         "category": "Error",
         "code": 18060
+    },
+    "'import.defer' must be followed by '('": {
+        "category": "Error",
+        "code": 18061
     }
 }

src/compiler/parser.ts

@@ -5939,7 +5939,18 @@ namespace Parser {
                 nextToken(); // advance past the 'import'
                 nextToken(); // advance past the dot
                 expression = finishNode(factory.createMetaProperty(SyntaxKind.ImportKeyword, parseIdentifierName()), pos);
-                sourceFlags |= NodeFlags.PossiblyContainsImportMeta;
+
+                if ((expression as MetaProperty).name.escapedText === "defer") {
+                    if (token() === SyntaxKind.OpenParenToken || token() === SyntaxKind.LessThanToken) {
+                        sourceFlags |= NodeFlags.PossiblyContainsDynamicImport;
+                    }
+                    else {
+                        parseErrorAt(pos, getNodePos(), Diagnostics.import_defer_must_be_followed_by);
+                    }
+                }
+                else {
+                    sourceFlags |= NodeFlags.PossiblyContainsImportMeta;
+                }
             }
             else {
                 expression = parseMemberExpressionOrHigher();

src/compiler/types.ts

@@ -3101,7 +3101,7 @@ export interface SuperCall extends CallExpression {
 }
 
 export interface ImportCall extends CallExpression {
-    readonly expression: ImportExpression;
+    readonly expression: ImportExpression | ImportDeferProperty;
 }
 
 export interface ExpressionWithTypeArguments extends MemberExpression, NodeWithTypeArguments {
@@ -3181,6 +3181,12 @@ export interface ImportMetaProperty extends MetaProperty {
     readonly name: Identifier & { readonly escapedText: __String & "meta"; };
 }
 
+/** @internal */
+export interface ImportDeferProperty extends MetaProperty {
+    readonly keywordToken: SyntaxKind.ImportKeyword;
+    readonly name: Identifier & { readonly escapedText: __String & "defer"; };
+}
+
 /// A JSX expression of the form <TagName attrs>...</TagName>
 export interface JsxElement extends PrimaryExpression {
     readonly kind: SyntaxKind.JsxElement;

src/compiler/utilities.ts

@@ -2632,7 +2632,13 @@ export function isSuperCall(n: Node): n is SuperCall {
 
 /** @internal */
 export function isImportCall(n: Node): n is ImportCall {
-    return n.kind === SyntaxKind.CallExpression && (n as CallExpression).expression.kind === SyntaxKind.ImportKeyword;
+    if (n.kind !== SyntaxKind.CallExpression) return false;
+    const e = (n as CallExpression).expression;
+    return e.kind === SyntaxKind.ImportKeyword || (
+        isMetaProperty(e)
+        && e.keywordToken === SyntaxKind.ImportKeyword
+        && e.name.escapedText === "defer"
+    );
 }
 
 /** @internal */

tests/baselines/reference/dynamicImportDefer.errors.txt

@@ -0,0 +1,20 @@
+error TS2468: Cannot find global value 'Promise'.
+b.ts(1,1): error TS2712: A dynamic import call in ES5 requires the 'Promise' constructor.  Make sure you have a declaration for the 'Promise' constructor or include 'ES2015' in your '--lib' option.
+b.ts(1,14): error TS2792: Cannot find module 'a'. Did you mean to set the 'moduleResolution' option to 'nodenext', or to add aliases to the 'paths' option?
+
+
+!!! error TS2468: Cannot find global value 'Promise'.
+==== a.ts (0 errors) ====
+    export function foo() {
+      console.log("foo from a");
+    }
+
+==== b.ts (2 errors) ====
+    import.defer("a").then(ns => {
+    ~~~~~~~~~~~~~~~~~
+!!! error TS2712: A dynamic import call in ES5 requires the 'Promise' constructor.  Make sure you have a declaration for the 'Promise' constructor or include 'ES2015' in your '--lib' option.
+                 ~~~
+!!! error TS2792: Cannot find module 'a'. Did you mean to set the 'moduleResolution' option to 'nodenext', or to add aliases to the 'paths' option?
+      ns.foo();
+    });
+

tests/baselines/reference/dynamicImportDefer.js

@@ -0,0 +1,21 @@
+//// [tests/cases/conformance/importDefer/dynamicImportDefer.ts] ////
+
+//// [a.ts]
+export function foo() {
+  console.log("foo from a");
+}
+
+//// [b.ts]
+import.defer("a").then(ns => {
+  ns.foo();
+});
+
+
+//// [a.js]
+export function foo() {
+    console.log("foo from a");
+}
+//// [b.js]
+import.defer("a").then(function (ns) {
+    ns.foo();
+});

tests/baselines/reference/dynamicImportDefer.symbols

@@ -0,0 +1,23 @@
+//// [tests/cases/conformance/importDefer/dynamicImportDefer.ts] ////
+
+=== a.ts ===
+export function foo() {
+>foo : Symbol(foo, Decl(a.ts, 0, 0))
+
+  console.log("foo from a");
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+}
+
+=== b.ts ===
+import.defer("a").then(ns => {
+>import.defer("a").then : Symbol(Promise.then, Decl(lib.es5.d.ts, --, --))
+>then : Symbol(Promise.then, Decl(lib.es5.d.ts, --, --))
+>ns : Symbol(ns, Decl(b.ts, 0, 23))
+
+  ns.foo();
+>ns : Symbol(ns, Decl(b.ts, 0, 23))
+
+});
+

tests/baselines/reference/dynamicImportDefer.types

@@ -0,0 +1,53 @@
+//// [tests/cases/conformance/importDefer/dynamicImportDefer.ts] ////
+
+=== a.ts ===
+export function foo() {
+>foo : () => void
+>    : ^^^^^^^^^^
+
+  console.log("foo from a");
+>console.log("foo from a") : void
+>                          : ^^^^
+>console.log : (...data: any[]) => void
+>            : ^^^^    ^^     ^^^^^    
+>console : Console
+>        : ^^^^^^^
+>log : (...data: any[]) => void
+>    : ^^^^    ^^     ^^^^^    
+>"foo from a" : "foo from a"
+>             : ^^^^^^^^^^^^
+}
+
+=== b.ts ===
+import.defer("a").then(ns => {
+>import.defer("a").then(ns => {  ns.foo();}) : Promise<void>
+>                                            : ^^^^^^^^^^^^^
+>import.defer("a").then : <TResult1 = any, TResult2 = never>(onfulfilled?: (value: any) => TResult1 | PromiseLike<TResult1>, onrejected?: (reason: any) => TResult2 | PromiseLike<TResult2>) => Promise<TResult1 | TResult2>
+>                       : ^        ^^^^^^^^        ^^^^^^^^^^           ^^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^          ^^^^      ^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>import.defer("a") : Promise<any>
+>                  : ^^^^^^^^^^^^
+>import.defer : any
+>             : ^^^
+>defer : any
+>      : ^^^
+>"a" : "a"
+>    : ^^^
+>then : <TResult1 = any, TResult2 = never>(onfulfilled?: (value: any) => TResult1 | PromiseLike<TResult1>, onrejected?: (reason: any) => TResult2 | PromiseLike<TResult2>) => Promise<TResult1 | TResult2>
+>     : ^        ^^^^^^^^        ^^^^^^^^^^           ^^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^          ^^^^      ^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>ns => {  ns.foo();} : (ns: any) => void
+>                    : ^  ^^^^^^^^^^^^^^
+>ns : any
+>   : ^^^
+
+  ns.foo();
+>ns.foo() : any
+>         : ^^^
+>ns.foo : any
+>       : ^^^
+>ns : any
+>   : ^^^
+>foo : any
+>    : ^^^
+
+});
+

tests/baselines/reference/dynamicImportDeferInvalidStandalone.errors.txt

@@ -0,0 +1,18 @@
+b.ts(1,1): error TS18061: 'import.defer' must be followed by '('
+b.ts(3,2): error TS18061: 'import.defer' must be followed by '('
+
+
+==== a.ts (0 errors) ====
+    export function foo() {
+      console.log("foo from a");
+    }
+
+==== b.ts (2 errors) ====
+    import.defer;
+    ~~~~~~~~~~~~
+!!! error TS18061: 'import.defer' must be followed by '('
+
+    (import.defer)("a");
+     ~~~~~~~~~~~~
+!!! error TS18061: 'import.defer' must be followed by '('
+

tests/baselines/reference/dynamicImportDeferInvalidStandalone.js

@@ -0,0 +1,20 @@
+//// [tests/cases/conformance/importDefer/dynamicImportDeferInvalidStandalone.ts] ////
+
+//// [a.ts]
+export function foo() {
+  console.log("foo from a");
+}
+
+//// [b.ts]
+import.defer;
+
+(import.defer)("a");
+
+
+//// [a.js]
+export function foo() {
+    console.log("foo from a");
+}
+//// [b.js]
+import.defer;
+(import.defer)("a");

tests/baselines/reference/dynamicImportDeferInvalidStandalone.symbols

@@ -0,0 +1,18 @@
+//// [tests/cases/conformance/importDefer/dynamicImportDeferInvalidStandalone.ts] ////
+
+=== a.ts ===
+export function foo() {
+>foo : Symbol(foo, Decl(a.ts, 0, 0))
+
+  console.log("foo from a");
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+}
+
+=== b.ts ===
+
+import.defer;
+
+(import.defer)("a");
+

tests/baselines/reference/dynamicImportDeferInvalidStandalone.types

@@ -0,0 +1,39 @@
+//// [tests/cases/conformance/importDefer/dynamicImportDeferInvalidStandalone.ts] ////
+
+=== a.ts ===
+export function foo() {
+>foo : () => void
+>    : ^^^^^^^^^^
+
+  console.log("foo from a");
+>console.log("foo from a") : void
+>                          : ^^^^
+>console.log : (...data: any[]) => void
+>            : ^^^^    ^^     ^^^^^    
+>console : Console
+>        : ^^^^^^^
+>log : (...data: any[]) => void
+>    : ^^^^    ^^     ^^^^^    
+>"foo from a" : "foo from a"
+>             : ^^^^^^^^^^^^
+}
+
+=== b.ts ===
+import.defer;
+>import.defer : any
+>             : ^^^
+>defer : any
+>      : ^^^
+
+(import.defer)("a");
+>(import.defer)("a") : any
+>                    : ^^^
+>(import.defer) : any
+>               : ^^^
+>import.defer : any
+>             : ^^^
+>defer : any
+>      : ^^^
+>"a" : "a"
+>    : ^^^
+

tests/baselines/reference/dynamicImportDeferMissingModuleESNext.errors.txt

@@ -0,0 +1,13 @@
+b.ts(1,1): error TS18060: Deferred imports are only supported when the '--module' flag is set to 'esnext'.
+b.ts(1,14): error TS2792: Cannot find module 'a'. Did you mean to set the 'moduleResolution' option to 'nodenext', or to add aliases to the 'paths' option?
+
+
+==== b.ts (2 errors) ====
+    import.defer("a").then(ns => {
+    ~~~~~~~~~~~~~~~~~
+!!! error TS18060: Deferred imports are only supported when the '--module' flag is set to 'esnext'.
+                 ~~~
+!!! error TS2792: Cannot find module 'a'. Did you mean to set the 'moduleResolution' option to 'nodenext', or to add aliases to the 'paths' option?
+      ns.foo();
+    });
+

tests/baselines/reference/dynamicImportDeferMissingModuleESNext.js

@@ -0,0 +1,12 @@
+//// [tests/cases/conformance/importDefer/dynamicImportDeferMissingModuleESNext.ts] ////
+
+//// [b.ts]
+import.defer("a").then(ns => {
+  ns.foo();
+});
+
+
+//// [b.js]
+import.defer("a").then(ns => {
+    ns.foo();
+});

tests/baselines/reference/dynamicImportDeferMissingModuleESNext.symbols

@@ -0,0 +1,13 @@
+//// [tests/cases/conformance/importDefer/dynamicImportDeferMissingModuleESNext.ts] ////
+
+=== b.ts ===
+import.defer("a").then(ns => {
+>import.defer("a").then : Symbol(Promise.then, Decl(lib.es5.d.ts, --, --))
+>then : Symbol(Promise.then, Decl(lib.es5.d.ts, --, --))
+>ns : Symbol(ns, Decl(b.ts, 0, 23))
+
+  ns.foo();
+>ns : Symbol(ns, Decl(b.ts, 0, 23))
+
+});
+