feat(linter): implement @typescript-eslint/no-non-null-assertion (#3825)

Related issue: https://github.com/oxc-project/oxc/issues/2180

original implementation

- code:
https://github.com/typescript-eslint/typescript-eslint/blob/main/packages/eslint-plugin/src/rules/no-non-null-assertion.ts
- test:
https://github.com/typescript-eslint/typescript-eslint/blob/main/packages/eslint-plugin/tests/rules/no-non-null-assertion.test.ts
- doc: https://typescript-eslint.io/rules/no-non-null-assertion/


typescript-eslint has a feature that is manually fixable by editor
suggestions on this rule, but oxc does not have one as far as I know, so
the implementation is simple compared to typescript-eslint

crates/oxc_linter/src/rules.rs

@@ -137,6 +137,7 @@ mod typescript {
     pub mod no_misused_new;
     pub mod no_namespace;
     pub mod no_non_null_asserted_optional_chain;
+    pub mod no_non_null_assertion;
     pub mod no_this_alias;
     pub mod no_unnecessary_type_constraint;
     pub mod no_unsafe_declaration_merging;
@@ -540,6 +541,7 @@ oxc_macros::declare_all_lint_rules! {
     typescript::triple_slash_reference,
     typescript::prefer_literal_enum_member,
     typescript::explicit_function_return_type,
+    typescript::no_non_null_assertion,
     jest::expect_expect,
     jest::max_expects,
     jest::max_nested_describe,

crates/oxc_linter/src/rules/typescript/no_non_null_assertion.rs

@@ -0,0 +1,87 @@
+use oxc_ast::AstKind;
+use oxc_diagnostics::OxcDiagnostic;
+use oxc_macros::declare_oxc_lint;
+use oxc_span::Span;
+
+use crate::{context::LintContext, rule::Rule, AstNode};
+
+#[derive(Debug, Default, Clone)]
+pub struct NoNonNullAssertion;
+
+declare_oxc_lint!(
+    /// ### What it does
+    /// Disallow non-null assertions using the ! postfix operator.
+    ///
+    /// ### Why is this bad?
+    /// TypeScript's ! non-null assertion operator asserts to the type system that an expression is non-nullable, as in not null or undefined. Using assertions to tell the type system new information is often a sign that code is not fully type-safe. It's generally better to structure program logic so that TypeScript understands when values may be nullable.
+    ///
+    /// ### Example
+    /// ```javascript
+    /// x!;
+    /// x!.y;
+    /// x.y!;
+    /// ```
+    NoNonNullAssertion,
+    restriction,
+);
+
+fn no_non_null_assertion_diagnostic(span0: Span) -> OxcDiagnostic {
+    OxcDiagnostic::warn("typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.")
+        .with_help("Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.")
+        .with_labels([span0.into()])
+}
+
+impl Rule for NoNonNullAssertion {
+    fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
+        let AstKind::TSNonNullExpression(expr) = node.kind() else { return };
+        ctx.diagnostic(no_non_null_assertion_diagnostic(expr.span));
+    }
+}
+
+#[test]
+fn test() {
+    use crate::tester::Tester;
+
+    let pass = vec!["x;", "x.y;", "x.y.z;", "x?.y.z;", "x?.y?.z;", "!x;"];
+
+    let fail = vec![
+        "x!;",
+        "x!.y;",
+        "x.y!;",
+        "!x!.y;",
+        "x!.y?.z;",
+        "x![y];",
+        "x![y]?.z;",
+        "x.y.z!();",
+        "x.y?.z!();",
+        "x!!!;",
+        "x!!.y;",
+        "x.y!!;",
+        "x.y.z!!();",
+        "x!?.[y].z;",
+        "x!?.y.z;",
+        "x.y.z!?.();",
+        "
+        	x!
+        	.y
+        	      ",
+        "
+        	x!
+        	// comment
+        	.y
+        	      ",
+        "
+        	x!
+        	 // comment
+        	    . /* comment */
+        	      y
+        	      ",
+        "
+        	x!
+        	 // comment
+        	     /* comment */ ['y']
+        	      ",
+    ];
+
+    Tester::new(NoNonNullAssertion::NAME, pass, fail).test_and_snapshot();
+}

crates/oxc_linter/src/snapshots/no_non_null_assertion.snap

@@ -0,0 +1,185 @@
+---
+source: crates/oxc_linter/src/tester.rs
+---
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!;
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!.y;
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x.y!;
+   · ────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:2]
+ 1 │ !x!.y;
+   ·  ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!.y?.z;
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x![y];
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x![y]?.z;
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x.y.z!();
+   · ──────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x.y?.z!();
+   · ───────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!!!;
+   · ────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!!!;
+   · ───
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!!!;
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!!.y;
+   · ───
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!!.y;
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x.y!!;
+   · ─────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x.y!!;
+   · ────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x.y.z!!();
+   · ───────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x.y.z!!();
+   · ──────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!?.[y].z;
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x!?.y.z;
+   · ──
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:1:1]
+ 1 │ x.y.z!?.();
+   · ──────
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:2:10]
+ 1 │ 
+ 2 │             x!
+   ·             ──
+ 3 │             .y
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:2:10]
+ 1 │ 
+ 2 │             x!
+   ·             ──
+ 3 │             // comment
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:2:10]
+ 1 │ 
+ 2 │             x!
+   ·             ──
+ 3 │              // comment
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.
+
+  ⚠ typescript-eslint(no-non-null-assertion): Forbidden non-null assertion.
+   ╭─[no_non_null_assertion.tsx:2:10]
+ 1 │ 
+ 2 │             x!
+   ·             ──
+ 3 │              // comment
+   ╰────
+  help: Consider using the optional chain operator `?.` instead. This operator includes runtime checks, so it is safer than the compile-only non-null assertion operator.