Fix #51623

src/compiler/checker.ts

@@ -14896,7 +14896,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     const resolved = resolveAlias(aliasSymbol);
                     if (resolved && resolved.flags & SymbolFlags.TypeAlias) {
                         newAliasSymbol = resolved;
-                        aliasTypeArguments = typeArgumentsFromTypeReferenceNode(node);
+                        aliasTypeArguments = typeArgumentsFromTypeReferenceNode(node) || (typeParameters ? [] : undefined);
                     }
                 }
             }

tests/baselines/reference/fixCrashAliasLookupForDefauledImport.js

@@ -0,0 +1,25 @@
+//// [tests/cases/compiler/fixCrashAliasLookupForDefauledImport.ts] ////
+
+//// [input.ts]
+export type Foo<T = string> = {};
+
+//// [usage.ts]
+import {Foo} from "./input";
+
+function bar<T>(element: Foo) {
+    return 1;
+}
+
+bar(1 as Foo<number>);
+
+
+//// [input.js]
+"use strict";
+exports.__esModule = true;
+//// [usage.js]
+"use strict";
+exports.__esModule = true;
+function bar(element) {
+    return 1;
+}
+bar(1);

tests/baselines/reference/fixCrashAliasLookupForDefauledImport.symbols

@@ -0,0 +1,22 @@
+=== tests/cases/compiler/input.ts ===
+export type Foo<T = string> = {};
+>Foo : Symbol(Foo, Decl(input.ts, 0, 0))
+>T : Symbol(T, Decl(input.ts, 0, 16))
+
+=== tests/cases/compiler/usage.ts ===
+import {Foo} from "./input";
+>Foo : Symbol(Foo, Decl(usage.ts, 0, 8))
+
+function bar<T>(element: Foo) {
+>bar : Symbol(bar, Decl(usage.ts, 0, 28))
+>T : Symbol(T, Decl(usage.ts, 2, 13))
+>element : Symbol(element, Decl(usage.ts, 2, 16))
+>Foo : Symbol(Foo, Decl(usage.ts, 0, 8))
+
+    return 1;
+}
+
+bar(1 as Foo<number>);
+>bar : Symbol(bar, Decl(usage.ts, 0, 28))
+>Foo : Symbol(Foo, Decl(usage.ts, 0, 8))
+

tests/baselines/reference/fixCrashAliasLookupForDefauledImport.types

@@ -0,0 +1,22 @@
+=== tests/cases/compiler/input.ts ===
+export type Foo<T = string> = {};
+>Foo : Foo<T>
+
+=== tests/cases/compiler/usage.ts ===
+import {Foo} from "./input";
+>Foo : any
+
+function bar<T>(element: Foo) {
+>bar : <T>(element: Foo) => number
+>element : Foo
+
+    return 1;
+>1 : 1
+}
+
+bar(1 as Foo<number>);
+>bar(1 as Foo<number>) : number
+>bar : <T>(element: Foo) => number
+>1 as Foo<number> : Foo<number>
+>1 : 1
+

tests/cases/compiler/fixCrashAliasLookupForDefauledImport.ts

@@ -0,0 +1,11 @@
+// @filename: input.ts
+export type Foo<T = string> = {};
+
+// @filename: usage.ts
+import {Foo} from "./input";
+
+function bar<T>(element: Foo) {
+    return 1;
+}
+
+bar(1 as Foo<number>);