feat(linter/eslint): add fixer to no-var (#5144)

crates/oxc_linter/src/rules/eslint/no_var.rs

@@ -1,4 +1,7 @@
-use oxc_ast::{ast::VariableDeclarationKind, AstKind};
+use oxc_ast::{
+    ast::{BindingPattern, BindingPatternKind, VariableDeclarationKind},
+    AstKind,
+};
 use oxc_diagnostics::OxcDiagnostic;
 use oxc_macros::declare_oxc_lint;
 use oxc_span::Span;
@@ -41,19 +44,57 @@ declare_oxc_lint!(
     /// ```
     NoVar,
     restriction,
-    pending // TODO: add suggestion that replaces `var` with `let` or `const` depending on if its written to
+    fix
 );
 
 impl Rule for NoVar {
     fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
         if let AstKind::VariableDeclaration(dec) = node.kind() {
             if dec.kind == VariableDeclarationKind::Var {
-                ctx.diagnostic(no_var_diagnostic(Span::new(dec.span.start, dec.span.start + 3)));
+                let is_written_to = dec.declarations.iter().any(|v| is_written_to(&v.id, ctx));
+
+                ctx.diagnostic_with_fix(
+                    no_var_diagnostic(Span::new(dec.span.start, dec.span.start + 3)),
+                    |fixer| {
+                        fixer.replace(
+                            Span::new(dec.span.start, dec.span.start + 3),
+                            if is_written_to { "let" } else { "const" },
+                        )
+                    },
+                );
             }
         }
     }
 }
 
+fn is_written_to(binding_pat: &BindingPattern, ctx: &LintContext) -> bool {
+    match &binding_pat.kind {
+        BindingPatternKind::BindingIdentifier(binding_ident) => ctx
+            .semantic()
+            .symbol_references(binding_ident.symbol_id.get().expect("symbol id should be set"))
+            .any(oxc_semantic::Reference::is_write),
+        BindingPatternKind::ObjectPattern(object_pat) => {
+            if object_pat.properties.iter().any(|prop| is_written_to(&prop.value, ctx)) {
+                return true;
+            }
+
+            if let Some(rest) = &object_pat.rest {
+                is_written_to(&rest.argument, ctx)
+            } else {
+                false
+            }
+        }
+        BindingPatternKind::AssignmentPattern(_) => true,
+        BindingPatternKind::ArrayPattern(array_pat) => array_pat.elements.iter().any(|elem| {
+            if let Some(elem) = elem {
+                is_written_to(elem, ctx)
+            } else {
+                false
+            }
+        }),
+    }
+}
+
 #[test]
 fn test() {
     use crate::tester::Tester;
@@ -109,5 +150,13 @@ fn test() {
         ("var bar = function () { foo(); }; var foo = function() {};", None),
     ];
 
-    Tester::new(NoVar::NAME, pass, fail).test_and_snapshot();
+    let fix = vec![
+        ("var foo", "const foo"),
+        ("var foo; foo += 1", "let foo; foo += 1"),
+        ("var foo,bar; bar = 'que'", "let foo,bar; bar = 'que'"),
+        ("var { a } = {}; a = fn()", "let { a } = {}; a = fn()"),
+        ("var { a } = {}; let b = a", "const { a } = {}; let b = a"),
+    ];
+
+    Tester::new(NoVar::NAME, pass, fail).expect_fix(fix).test_and_snapshot();
 }