Fix #21848: Allows to mutate const with non-null assertion (#21873)

src/compiler/utilities.ts

@@ -1754,6 +1754,7 @@ namespace ts {
                 case SyntaxKind.ParenthesizedExpression:
                 case SyntaxKind.ArrayLiteralExpression:
                 case SyntaxKind.SpreadElement:
+                case SyntaxKind.NonNullExpression:
                     node = parent;
                     break;
                 case SyntaxKind.ShorthandPropertyAssignment:

tests/baselines/reference/constWithNonNull.errors.txt

@@ -0,0 +1,11 @@
+tests/cases/compiler/constWithNonNull.ts(4,1): error TS2540: Cannot assign to 'x' because it is a constant or a read-only property.
+
+
+==== tests/cases/compiler/constWithNonNull.ts (1 errors) ====
+    // Fixes #21848
+    
+    declare const x: number | undefined;
+    x!++;
+    ~
+!!! error TS2540: Cannot assign to 'x' because it is a constant or a read-only property.
+    

tests/baselines/reference/constWithNonNull.js

@@ -0,0 +1,10 @@
+//// [constWithNonNull.ts]
+// Fixes #21848
+
+declare const x: number | undefined;
+x!++;
+
+
+//// [constWithNonNull.js]
+// Fixes #21848
+x++;

tests/baselines/reference/constWithNonNull.symbols

@@ -0,0 +1,9 @@
+=== tests/cases/compiler/constWithNonNull.ts ===
+// Fixes #21848
+
+declare const x: number | undefined;
+>x : Symbol(x, Decl(constWithNonNull.ts, 2, 13))
+
+x!++;
+>x : Symbol(x, Decl(constWithNonNull.ts, 2, 13))
+

tests/baselines/reference/constWithNonNull.types

@@ -0,0 +1,11 @@
+=== tests/cases/compiler/constWithNonNull.ts ===
+// Fixes #21848
+
+declare const x: number | undefined;
+>x : number
+
+x!++;
+>x!++ : number
+>x! : any
+>x : any
+

tests/cases/compiler/constWithNonNull.ts

@@ -0,0 +1,4 @@
+// Fixes #21848
+
+declare const x: number | undefined;
+x!++;