Fix crash getting error for type alias index signature without a type

src/compiler/checker.ts

@@ -31005,7 +31005,7 @@ namespace ts {
                                               Diagnostics.An_index_signature_parameter_type_cannot_be_a_type_alias_Consider_writing_0_Colon_1_Colon_2_instead,
                                               getTextOfNode(parameter.name),
                                               typeToString(type),
-                                              typeToString(getTypeFromTypeNode(node.type!)));
+                                              typeToString(node.type ? getTypeFromTypeNode(node.type) : anyType));
                 }
 
                 if (type.flags & TypeFlags.Union && allTypesAssignableToKind(type, TypeFlags.StringLiteral, /*strict*/ true)) {

tests/baselines/reference/indexerConstraints2.errors.txt

@@ -9,9 +9,10 @@ tests/cases/compiler/indexerConstraints2.ts(58,6): error TS1023: An index signat
 tests/cases/compiler/indexerConstraints2.ts(64,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
 tests/cases/compiler/indexerConstraints2.ts(70,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
 tests/cases/compiler/indexerConstraints2.ts(74,6): error TS1337: An index signature parameter type cannot be a union type. Consider using a mapped object type instead.
+tests/cases/compiler/indexerConstraints2.ts(79,6): error TS1336: An index signature parameter type cannot be a type alias. Consider writing '[key: string]: any' instead.
 
 
-==== tests/cases/compiler/indexerConstraints2.ts (11 errors) ====
+==== tests/cases/compiler/indexerConstraints2.ts (12 errors) ====
     class A { a: number; }
     class B extends A { b: number; }
     
@@ -108,4 +109,12 @@ tests/cases/compiler/indexerConstraints2.ts(74,6): error TS1337: An index signat
         [u: "foo" | "bar"]: A;
          ~
 !!! error TS1337: An index signature parameter type cannot be a union type. Consider using a mapped object type instead.
-    }
+    }
+    
+    type Key = string;
+    interface T {
+        [key: Key]
+         ~~~
+!!! error TS1336: An index signature parameter type cannot be a type alias. Consider writing '[key: string]: any' instead.
+    }
+    

tests/baselines/reference/indexerConstraints2.js

@@ -73,7 +73,13 @@ interface R {
 
 interface S {
     [u: "foo" | "bar"]: A;
-}
+}
+
+type Key = string;
+interface T {
+    [key: Key]
+}
+
 
 //// [indexerConstraints2.js]
 var __extends = (this && this.__extends) || (function () {

tests/baselines/reference/indexerConstraints2.symbols

@@ -155,3 +155,15 @@ interface S {
 >u : Symbol(u, Decl(indexerConstraints2.ts, 73, 5))
 >A : Symbol(A, Decl(indexerConstraints2.ts, 0, 0))
 }
+
+type Key = string;
+>Key : Symbol(Key, Decl(indexerConstraints2.ts, 74, 1))
+
+interface T {
+>T : Symbol(T, Decl(indexerConstraints2.ts, 76, 18))
+
+    [key: Key]
+>key : Symbol(key, Decl(indexerConstraints2.ts, 78, 5))
+>Key : Symbol(Key, Decl(indexerConstraints2.ts, 74, 1))
+}
+

tests/baselines/reference/indexerConstraints2.types

@@ -118,3 +118,12 @@ interface S {
     [u: "foo" | "bar"]: A;
 >u : IndexableUnion
 }
+
+type Key = string;
+>Key : string
+
+interface T {
+    [key: Key]
+>key : string
+}
+

tests/cases/compiler/indexerConstraints2.ts

@@ -72,4 +72,9 @@ interface R {
 
 interface S {
     [u: "foo" | "bar"]: A;
-}
+}
+
+type Key = string;
+interface T {
+    [key: Key]
+}