fix #11463, null assertion block uninitialized error (#14020)

Author: HerringtonDarkholme

src/compiler/checker.ts

@@ -12035,6 +12035,7 @@ namespace ts {
             // declaration container are the same).
             const assumeInitialized = isParameter || isOuterVariable ||
                 type !== autoType && type !== autoArrayType && (!strictNullChecks || (type.flags & TypeFlags.Any) !== 0 || isInTypeQuery(node) || node.parent.kind === SyntaxKind.ExportSpecifier) ||
+                node.parent.kind === SyntaxKind.NonNullExpression ||
                 isInAmbientContext(declaration);
             const initialType = assumeInitialized ? (isParameter ? removeOptionalityFromDeclaredType(type, getRootDeclaration(declaration) as VariableLikeDeclaration) : type) :
                 type === autoType || type === autoArrayType ? undefinedType :

tests/baselines/reference/typeGuardsAsAssertions.js

@@ -119,6 +119,11 @@ function f6() {
     x = <string | null>"";
     x!.slice();
 }
+
+function f7() {
+    let x: string;
+    x!.slice();
+}
 
 
 //// [typeGuardsAsAssertions.js]
@@ -227,3 +232,7 @@ function f6() {
     x = "";
     x.slice();
 }
+function f7() {
+    var x;
+    x.slice();
+}

tests/baselines/reference/typeGuardsAsAssertions.symbols

@@ -312,3 +312,15 @@ function f6() {
 >slice : Symbol(String.slice, Decl(lib.d.ts, --, --))
 }
 
+function f7() {
+>f7 : Symbol(f7, Decl(typeGuardsAsAssertions.ts, 119, 1))
+
+    let x: string;
+>x : Symbol(x, Decl(typeGuardsAsAssertions.ts, 122, 7))
+
+    x!.slice();
+>x!.slice : Symbol(String.slice, Decl(lib.d.ts, --, --))
+>x : Symbol(x, Decl(typeGuardsAsAssertions.ts, 122, 7))
+>slice : Symbol(String.slice, Decl(lib.d.ts, --, --))
+}
+

tests/baselines/reference/typeGuardsAsAssertions.types

@@ -382,3 +382,17 @@ function f6() {
 >slice : (start?: number | undefined, end?: number | undefined) => string
 }
 
+function f7() {
+>f7 : () => void
+
+    let x: string;
+>x : string
+
+    x!.slice();
+>x!.slice() : string
+>x!.slice : (start?: number | undefined, end?: number | undefined) => string
+>x! : string
+>x : string
+>slice : (start?: number | undefined, end?: number | undefined) => string
+}
+

tests/cases/conformance/controlFlow/typeGuardsAsAssertions.ts

@@ -120,3 +120,8 @@ function f6() {
     x = <string | null>"";
     x!.slice();
 }
+
+function f7() {
+    let x: string;
+    x!.slice();
+}