1 use crate::utils::span_lint_and_help;
2 use rustc_ast::ast::{Block, Expr, ExprKind, Stmt, StmtKind};
3 use rustc_ast::visit::{walk_expr, Visitor};
4 use rustc_lint::{EarlyContext, EarlyLintPass};
5 use rustc_middle::lint::in_external_macro;
6 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 /// **What it does:** Checks for `else` blocks that can be removed without changing semantics.
11 /// **Why is this bad?** The `else` block adds unnecessary indentation and verbosity.
13 /// **Known problems:** Some may prefer to keep the `else` block for clarity.
18 /// fn my_func(count: u32) {
20 /// print!("Nothing to do");
23 /// print!("Moving on...");
29 /// fn my_func(count: u32) {
31 /// print!("Nothing to do");
34 /// print!("Moving on...");
39 "`else` branch that can be removed without changing semantics"
42 declare_lint_pass!(RedundantElse => [REDUNDANT_ELSE]);
44 impl EarlyLintPass for RedundantElse {
45 fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &Stmt) {
46 if in_external_macro(cx.sess, stmt.span) {
49 // Only look at expressions that are a whole statement
50 let expr: &Expr = match &stmt.kind {
51 StmtKind::Expr(expr) | StmtKind::Semi(expr) => expr,
55 let (mut then, mut els): (&Block, &Expr) = match &expr.kind {
56 ExprKind::If(_, then, Some(els)) => (then, els),
60 if !BreakVisitor::default().check_block(then) {
61 // then block does not always break
66 ExprKind::If(_, next_then, Some(next_els)) => {
71 // else if without else
72 ExprKind::If(..) => return,
81 "redundant else block",
83 "remove the `else` block and move the contents out",
88 /// Call `check` functions to check if an expression always breaks control flow
94 impl<'ast> Visitor<'ast> for BreakVisitor {
95 fn visit_block(&mut self, block: &'ast Block) {
96 self.is_break = match block.stmts.as_slice() {
97 [.., last] => self.check_stmt(last),
102 fn visit_expr(&mut self, expr: &'ast Expr) {
103 self.is_break = match expr.kind {
104 ExprKind::Break(..) | ExprKind::Continue(..) | ExprKind::Ret(..) => true,
105 ExprKind::Match(_, ref arms) => arms.iter().all(|arm| self.check_expr(&arm.body)),
106 ExprKind::If(_, ref then, Some(ref els)) => self.check_block(then) && self.check_expr(els),
107 ExprKind::If(_, _, None)
108 // ignore loops for simplicity
109 | ExprKind::While(..) | ExprKind::ForLoop(..) | ExprKind::Loop(..) => false,
111 walk_expr(self, expr);
119 fn check<T>(&mut self, item: T, visit: fn(&mut Self, T)) -> bool {
121 std::mem::replace(&mut self.is_break, false)
124 fn check_block(&mut self, block: &Block) -> bool {
125 self.check(block, Self::visit_block)
128 fn check_expr(&mut self, expr: &Expr) -> bool {
129 self.check(expr, Self::visit_expr)
132 fn check_stmt(&mut self, stmt: &Stmt) -> bool {
133 self.check(stmt, Self::visit_stmt)