Fix printing and emit for definite assignment assertions

src/compiler/binder.ts

@@ -3807,7 +3807,7 @@ namespace ts {
         }
 
         // Type annotations are TypeScript syntax.
-        if (node.type) {
+        if (node.type || node.exclamationToken) {
             transformFlags |= TransformFlags.AssertTypeScript;
         }
 

src/compiler/emitter.ts

@@ -2741,6 +2741,7 @@ namespace ts {
 
         function emitVariableDeclaration(node: VariableDeclaration) {
             emit(node.name);
+            emit(node.exclamationToken);
             emitTypeAnnotation(node.type);
             emitInitializer(node.initializer, node.type ? node.type.end : node.name.end, node);
         }

src/compiler/factory.ts

@@ -1937,6 +1937,7 @@ namespace ts {
     }
 
     export function createVariableDeclaration(name: string | BindingName, type?: TypeNode, initializer?: Expression) {
+        /* Internally, one should probably use createTypeScriptVariableDeclaration instead and handle definite assignment assertions */
         const node = <VariableDeclaration>createSynthesizedNode(SyntaxKind.VariableDeclaration);
         node.name = asName(name);
         node.type = type;
@@ -1945,13 +1946,34 @@ namespace ts {
     }
 
     export function updateVariableDeclaration(node: VariableDeclaration, name: BindingName, type: TypeNode | undefined, initializer: Expression | undefined) {
+        /* Internally, one should probably use updateTypeScriptVariableDeclaration instead and handle definite assignment assertions */
         return node.name !== name
             || node.type !== type
             || node.initializer !== initializer
             ? updateNode(createVariableDeclaration(name, type, initializer), node)
             : node;
     }
 
+    /* @internal */
+    export function createTypeScriptVariableDeclaration(name: string | BindingName, exclaimationToken?: Token<SyntaxKind.ExclamationToken>, type?: TypeNode, initializer?: Expression) {
+        const node = <VariableDeclaration>createSynthesizedNode(SyntaxKind.VariableDeclaration);
+        node.name = asName(name);
+        node.type = type;
+        node.initializer = initializer !== undefined ? parenthesizeExpressionForList(initializer) : undefined;
+        node.exclamationToken = exclaimationToken;
+        return node;
+    }
+
+    /* @internal */
+    export function updateTypeScriptVariableDeclaration(node: VariableDeclaration, name: BindingName, exclaimationToken: Token<SyntaxKind.ExclamationToken> | undefined, type: TypeNode | undefined, initializer: Expression | undefined) {
+        return node.name !== name
+            || node.type !== type
+            || node.initializer !== initializer
+            || node.exclamationToken !== exclaimationToken
+            ? updateNode(createTypeScriptVariableDeclaration(name, exclaimationToken, type, initializer), node)
+            : node;
+    }
+
     export function createVariableDeclarationList(declarations: readonly VariableDeclaration[], flags = NodeFlags.None) {
         const node = <VariableDeclarationList>createSynthesizedNode(SyntaxKind.VariableDeclarationList);
         node.flags |= flags & NodeFlags.BlockScoped;

src/compiler/transformers/declarations.ts

@@ -937,7 +937,7 @@ namespace ts {
                         }
                         shouldEnterSuppressNewDiagnosticsContextContext = true;
                         suppressNewDiagnosticContexts = true; // Variable declaration types also suppress new diagnostic contexts, provided the contexts wouldn't be made for binding pattern types
-                        return cleanup(updateVariableDeclaration(input, input.name, ensureType(input, input.type), ensureNoInitializer(input)));
+                        return cleanup(updateTypeScriptVariableDeclaration(input, input.name, /*exclaimationToken*/ undefined, ensureType(input, input.type), ensureNoInitializer(input)));
                     }
                     case SyntaxKind.TypeParameter: {
                         if (isPrivateMethodTypeParameter(input) && (input.default || input.constraint)) {

src/compiler/transformers/ts.ts

@@ -2188,9 +2188,10 @@ namespace ts {
         }
 
         function visitVariableDeclaration(node: VariableDeclaration) {
-            return updateVariableDeclaration(
+            return updateTypeScriptVariableDeclaration(
                 node,
                 visitNode(node.name, visitor, isBindingName),
+                /*exclaimationToken*/ undefined,
                 /*type*/ undefined,
                 visitNode(node.initializer, visitor, isExpression));
         }

src/testRunner/unittests/printer.ts

@@ -67,6 +67,17 @@ namespace ts {
                 `class A extends B implements C implements D {}`,
                 ScriptTarget.ES2017
             )));
+
+            // github #35093
+            printsCorrectly("definiteAssignmentAssertions", {}, printer => printer.printFile(createSourceFile(
+                "source.ts",
+                `class A {
+                    prop!: string;
+                }
+
+                let x!: string;`,
+                ScriptTarget.ES2017
+            )));
         });
 
         describe("printBundle", () => {

tests/baselines/reference/printerApi/printsFileCorrectly.definiteAssignmentAssertions.js

@@ -0,0 +1,4 @@
+class A {
+    prop!: string;
+}
+let x!: string;