docs(ast): clarify TSNonNullExpression docs (#26960)

Follow-up to [review feedback](https://github.com/oxc-project/oxc/pull/26910#discussion_r4070637601): clarify that `!` removes both `null` and `undefined` from its type.

crates/oxc_ast/src/ast/ts.rs

@@ -1745,8 +1745,8 @@ pub struct TSExternalModuleReference<'a> {
 
 /// TypeScript non-null expression (`!`)
 ///
-/// This expression assumes that the type of the inner expression is not null
-/// and changes it from `T | null` to just `T`.
+/// This expression asserts that the inner expression is neither `null` nor `undefined`,
+/// removing both from its type (for example, `T | null | undefined` becomes `T`).
 ///
 /// ## Example
 ///
@@ -1764,7 +1764,7 @@ pub struct TSExternalModuleReference<'a> {
 pub struct TSNonNullExpression<'a> {
     pub node_id: Cell<NodeId>,
     pub span: Span,
-    /// The expression to assume as not null, e.g., `x` in `x!`.
+    /// The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     pub expression: Expression<'a>,
 }
 

crates/oxc_ast/src/generated/ast_builder.rs

@@ -1173,7 +1173,7 @@ impl<'a> Expression<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -2701,7 +2701,7 @@ impl<'a> ArrayExpressionElement<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -4136,7 +4136,7 @@ impl<'a> PropertyKey<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -6078,7 +6078,7 @@ impl<'a> Argument<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -6628,7 +6628,7 @@ impl<'a> AssignmentTarget<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -6878,7 +6878,7 @@ impl<'a> SimpleAssignmentTarget<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -7281,7 +7281,7 @@ impl<'a> AssignmentTargetMaybeDefault<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -7837,7 +7837,7 @@ impl<'a> ChainElement<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -11414,7 +11414,7 @@ impl<'a> ForStatementInit<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -11778,7 +11778,7 @@ impl<'a> ForStatementLeft<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -14476,7 +14476,7 @@ impl<'a> ArrowFunctionBody<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -17945,7 +17945,7 @@ impl<'a> ExportDefaultDeclarationKind<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -20136,7 +20136,7 @@ impl<'a> JSXExpression<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new_ts_non_null_expression(
         span: Span,
@@ -27044,7 +27044,7 @@ impl<'a> TSNonNullExpression<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn new(span: Span, expression: Expression<'a>, builder: &impl GetAstBuilder<'a>) -> Self {
         let builder = builder.builder();
@@ -27058,7 +27058,7 @@ impl<'a> TSNonNullExpression<'a> {
     ///
     /// ## Parameters
     /// * `span`: The [`Span`] covering this node
-    /// * `expression`: The expression to assume as not null, e.g., `x` in `x!`.
+    /// * `expression`: The expression to assert as neither `null` nor `undefined`, e.g., `x` in `x!`.
     #[inline]
     pub fn boxed(
         span: Span,