feat(linter): eslint-plugin-unicorn no-null(style) (#1705)

Try to implement
[no-null](https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/no-null.md)
for #684 .

crates/oxc_linter/src/rules.rs

@@ -171,6 +171,7 @@ mod unicorn {
     pub mod no_nested_ternary;
     pub mod no_new_array;
     pub mod no_new_buffer;
+    pub mod no_null;
     pub mod no_object_as_default_parameter;
     pub mod no_static_only_class;
     pub mod no_thenable;
@@ -372,6 +373,7 @@ oxc_macros::declare_all_lint_rules! {
     unicorn::no_nested_ternary,
     unicorn::no_new_array,
     unicorn::no_new_buffer,
+    unicorn::no_null,
     unicorn::no_object_as_default_parameter,
     unicorn::no_static_only_class,
     unicorn::no_thenable,

crates/oxc_linter/src/rules/unicorn/no_null.rs

@@ -0,0 +1,309 @@
+use oxc_ast::{
+    ast::{
+        Argument, BinaryExpression, CallExpression, Expression, NullLiteral, VariableDeclarator,
+    },
+    AstKind,
+};
+use oxc_diagnostics::{
+    miette::{self, Diagnostic},
+    thiserror::Error,
+};
+use oxc_macros::declare_oxc_lint;
+use oxc_span::{GetSpan, Span};
+use oxc_syntax::operator::BinaryOperator;
+
+use crate::{ast_util::is_method_call, context::LintContext, rule::Rule, AstNode, Fix};
+
+#[derive(Debug, Error, Diagnostic)]
+#[error("eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal")]
+#[diagnostic(severity(warning), help("Replace the `null` literal with `undefined`."))]
+struct ReplaceNullDiagnostic(#[label] pub Span);
+
+#[derive(Debug, Error, Diagnostic)]
+#[error("eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal")]
+#[diagnostic(severity(warning), help("Remove the `null` literal."))]
+struct RemoveNullDiagnostic(#[label] pub Span);
+
+#[derive(Debug, Default, Clone)]
+pub struct NoNull {
+    check_strict_equality: Option<bool>,
+}
+
+declare_oxc_lint!(
+    /// ### What it does
+    ///
+    /// Disallow the use of the `null` literal, to encourage using `undefined` instead.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// There are some reasons for using `undefined` instead of `null`.
+    /// - From experience, most developers use `null` and `undefined` inconsistently and interchangeably, and few know when to use which.
+    /// - Supporting both `null` and `undefined` complicates input validation.
+    /// - Using `null` makes TypeScript types more verbose: `type A = {foo?: string | null}` vs `type A = {foo?: string}`.
+    ///
+    /// ### Example
+    /// ```javascript
+    /// // Bad
+    /// let foo = null;
+    ///
+    /// // Good
+    /// let foo
+    /// ```
+    NoNull,
+    style
+);
+
+fn match_null_arg(call_expr: &CallExpression, index: usize, span: Span) -> bool {
+    call_expr.arguments.get(index).map_or(false, |arg| {
+        if let Argument::Expression(Expression::NullLiteral(null_lit)) = arg {
+            return null_lit.span == span;
+        }
+
+        false
+    })
+}
+
+fn diagnose_binary_expression(
+    no_null: &NoNull,
+    ctx: &LintContext,
+    null_literal: &NullLiteral,
+    binary_expr: &BinaryExpression,
+) {
+    // checkStrictEquality=false && `if (foo !== null) {}`
+    if !no_null.check_strict_equality.is_some_and(|val| val)
+        && matches!(
+            binary_expr.operator,
+            BinaryOperator::StrictEquality | BinaryOperator::StrictInequality
+        )
+    {
+        return;
+    }
+
+    // `if (foo != null) {}`
+    if matches!(binary_expr.operator, BinaryOperator::Equality | BinaryOperator::Inequality) {
+        ctx.diagnostic_with_fix(ReplaceNullDiagnostic(null_literal.span), || {
+            Fix::new("undefined", null_literal.span)
+        });
+
+        return;
+    }
+
+    // checkStrictEquality=true && `if (foo !== null) {}`
+    ctx.diagnostic_with_fix(ReplaceNullDiagnostic(null_literal.span), || {
+        Fix::new("undefined", null_literal.span)
+    });
+}
+
+fn diagnose_variable_declarator(
+    ctx: &LintContext,
+    null_literal: &NullLiteral,
+    variable_declarator: &VariableDeclarator,
+    parent_kind: Option<AstKind>,
+) {
+    // `let foo = null;`
+    if matches!(&variable_declarator.init, Some(Expression::NullLiteral(expr)) if expr.span == null_literal.span)
+        && matches!(parent_kind, Some(AstKind::VariableDeclaration(var_declaration)) if !var_declaration.kind.is_const() )
+    {
+        ctx.diagnostic_with_fix(RemoveNullDiagnostic(null_literal.span), || {
+            Fix::delete(Span {
+                start: variable_declarator.id.span().end,
+                end: null_literal.span.end,
+            })
+        });
+
+        return;
+    }
+
+    // `const foo = null`
+    ctx.diagnostic_with_fix(ReplaceNullDiagnostic(null_literal.span), || {
+        Fix::new("undefined", null_literal.span)
+    });
+}
+
+fn match_call_expression_pass_case(null_literal: &NullLiteral, call_expr: &CallExpression) -> bool {
+    // `Object.create(null)`, `Object.create(null, foo)`
+    if is_method_call(call_expr, Some(&["Object"]), Some(&["create"]), Some(1), Some(2))
+        && !call_expr.optional
+        && !matches!(&call_expr.callee, Expression::MemberExpression(member_expr) if member_expr.is_computed())
+        && match_null_arg(call_expr, 0, null_literal.span)
+    {
+        return true;
+    }
+
+    // `useRef(null)`
+    if let Expression::Identifier(ident) = &call_expr.callee {
+        if ident.name == "useRef" && call_expr.arguments.len() == 1 && !call_expr.optional {
+            return true;
+        }
+    }
+
+    // `React.useRef(null)`
+    if is_method_call(call_expr, Some(&["React"]), Some(&["useRef"]), Some(1), Some(1))
+        && !call_expr.optional
+    {
+        return true;
+    }
+
+    // `foo.insertBefore(bar, null)`
+    if is_method_call(call_expr, None, Some(&["insertBefore"]), Some(2), Some(2))
+        && !call_expr
+            .arguments
+            .iter()
+            .any(|argument| matches!(argument, Argument::SpreadElement(_)))
+        && !call_expr.optional
+        && !matches!(&call_expr.callee, Expression::MemberExpression(member_expr) if member_expr.is_computed())
+        && match_null_arg(call_expr, 1, null_literal.span)
+    {
+        return true;
+    }
+
+    false
+}
+
+impl Rule for NoNull {
+    fn from_configuration(value: serde_json::Value) -> Self {
+        Self {
+            check_strict_equality: value
+                .get(0)
+                .and_then(|v| v.get("checkStrictEquality"))
+                .and_then(serde_json::Value::as_bool),
+        }
+    }
+
+    fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
+        let AstKind::NullLiteral(null_literal) = node.kind() else {
+            return;
+        };
+
+        if let Some(parent_node) = ctx.nodes().parent_node(node.id()) {
+            let grand_parent_kind = ctx.nodes().parent_kind(parent_node.id());
+
+            if matches!(parent_node.kind(), AstKind::Argument(_)) {
+                if let Some(AstKind::CallExpression(call_expr)) = grand_parent_kind {
+                    if match_call_expression_pass_case(null_literal, call_expr) {
+                        return;
+                    }
+                }
+            }
+
+            if let AstKind::BinaryExpression(binary_expr) = parent_node.kind() {
+                diagnose_binary_expression(self, ctx, null_literal, binary_expr);
+                return;
+            }
+
+            if let AstKind::VariableDeclarator(variable_declarator) = parent_node.kind() {
+                diagnose_variable_declarator(
+                    ctx,
+                    null_literal,
+                    variable_declarator,
+                    grand_parent_kind,
+                );
+
+                return;
+            }
+
+            // `function foo() { return null; }`,
+            if matches!(parent_node.kind(), AstKind::ReturnStatement(_)) {
+                ctx.diagnostic_with_fix(RemoveNullDiagnostic(null_literal.span), || {
+                    Fix::delete(null_literal.span)
+                });
+
+                return;
+            }
+        }
+
+        ctx.diagnostic_with_fix(ReplaceNullDiagnostic(null_literal.span), || {
+            Fix::new("undefined", null_literal.span)
+        });
+    }
+}
+
+#[test]
+fn test() {
+    use crate::tester::Tester;
+
+    fn check_strict_equality(option: bool) -> serde_json::Value {
+        serde_json::json!([{
+            "checkStrictEquality": option,
+        }])
+    }
+
+    let pass = vec![
+        ("let foo", None),
+        ("Object.create(null)", None),
+        ("Object.create(null, {foo: {value:1}})", None),
+        ("let insertedNode = parentNode.insertBefore(newNode, null)", None),
+        ("const foo = \"null\";", None),
+        ("Object.create()", None),
+        ("Object.create(bar)", None),
+        ("Object.create(\"null\")", None),
+        ("useRef(null)", None),
+        ("React.useRef(null)", None),
+        ("if (foo === null) {}", None),
+        ("if (null === foo) {}", None),
+        ("if (foo !== null) {}", None),
+        ("if (null !== foo) {}", None),
+        ("foo = Object.create(null)", None),
+        ("if (foo === null) {}", Some(check_strict_equality(false))),
+        ("if (null === foo) {}", Some(check_strict_equality(false))),
+        ("if (foo !== null) {}", Some(check_strict_equality(false))),
+        ("if (null !== foo) {}", Some(check_strict_equality(false))),
+    ];
+
+    let fail = vec![
+        ("const foo = null", None),
+        ("foo(null)", None),
+        ("if (foo == null) {}", None),
+        ("if (foo != null) {}", None),
+        ("if (null == foo) {}", None),
+        ("if (null != foo) {}", None),
+        // Suggestion `ReturnStatement`
+        (
+            "function foo() {
+            return null;
+            }",
+            None,
+        ),
+        // Suggestion `VariableDeclaration`
+        ("let foo = null;", None),
+        ("var foo = null;", None),
+        ("var foo = 1, bar = null, baz = 2;", None),
+        ("const foo = null;", None),
+        // `checkStrictEquality`
+        ("if (foo === null) {}", Some(check_strict_equality(true))),
+        ("if (null === foo) {}", Some(check_strict_equality(true))),
+        ("if (foo !== null) {}", Some(check_strict_equality(true))),
+        ("if (null !== foo) {}", Some(check_strict_equality(true))),
+        // Not `CallExpression`
+        ("new Object.create(null)", None),
+        ("new foo.insertBefore(bar, null)", None),
+        // Not `MemberExpression`
+        ("create(null)", None),
+        ("insertBefore(bar, null)", None),
+        // `callee.property` is not a `Identifier`
+        ("Object['create'](null)", None),
+        ("foo['insertBefore'](bar, null)", None),
+        // Computed
+        ("Object[create](null)", None),
+        ("foo[insertBefore](bar, null)", None),
+        ("Object[null](null)", None),
+        // Not matching method
+        ("Object.notCreate(null)", None),
+        ("foo.notInsertBefore(foo, null)", None),
+        // Not `Object`
+        ("NotObject.create(null)", None),
+        // `callee.object.type` is not a `Identifier`
+        ("lib.Object.create(null)", None),
+        // More/Less arguments
+        ("Object.create(...[null])", None),
+        ("Object.create(null, bar, extraArgument)", None),
+        ("foo.insertBefore(null)", None),
+        ("foo.insertBefore(foo, null, bar)", None),
+        ("foo.insertBefore(...[foo], null)", None),
+        // Not in right position
+        ("foo.insertBefore(null, bar)", None),
+        ("Object.create(bar, null)", None),
+    ];
+
+    Tester::new(NoNull::NAME, pass, fail).test_and_snapshot();
+}

crates/oxc_linter/src/snapshots/no_null.snap

@@ -0,0 +1,259 @@
+---
+source: crates/oxc_linter/src/tester.rs
+expression: no_null
+---
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ const foo = null
+   ·             ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ foo(null)
+   ·     ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ if (foo == null) {}
+   ·            ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ if (foo != null) {}
+   ·            ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ if (null == foo) {}
+   ·     ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ if (null != foo) {}
+   ·     ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ function foo() {
+ 2 │             return null;
+   ·                    ────
+ 3 │             }
+   ╰────
+  help: Remove the `null` literal.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ let foo = null;
+   ·           ────
+   ╰────
+  help: Remove the `null` literal.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ var foo = null;
+   ·           ────
+   ╰────
+  help: Remove the `null` literal.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ var foo = 1, bar = null, baz = 2;
+   ·                    ────
+   ╰────
+  help: Remove the `null` literal.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ const foo = null;
+   ·             ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ if (foo === null) {}
+   ·             ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ if (null === foo) {}
+   ·     ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ if (foo !== null) {}
+   ·             ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ if (null !== foo) {}
+   ·     ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ new Object.create(null)
+   ·                   ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ new foo.insertBefore(bar, null)
+   ·                           ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ create(null)
+   ·        ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ insertBefore(bar, null)
+   ·                   ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ Object['create'](null)
+   ·                  ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ foo['insertBefore'](bar, null)
+   ·                          ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ Object[create](null)
+   ·                ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ foo[insertBefore](bar, null)
+   ·                        ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ Object[null](null)
+   ·              ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ Object[null](null)
+   ·        ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ Object.notCreate(null)
+   ·                  ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ foo.notInsertBefore(foo, null)
+   ·                          ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ NotObject.create(null)
+   ·                  ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ lib.Object.create(null)
+   ·                   ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ Object.create(...[null])
+   ·                   ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ Object.create(null, bar, extraArgument)
+   ·               ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ foo.insertBefore(null)
+   ·                  ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ foo.insertBefore(foo, null, bar)
+   ·                       ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ foo.insertBefore(...[foo], null)
+   ·                            ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ foo.insertBefore(null, bar)
+   ·                  ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+  ⚠ eslint-plugin-unicorn(no-null): Disallow the use of the `null` literal
+   ╭─[no_null.tsx:1:1]
+ 1 │ Object.create(bar, null)
+   ·                    ────
+   ╰────
+  help: Replace the `null` literal with `undefined`.
+
+