| use clippy_utils::diagnostics::span_lint_and_help; |
| use rustc_ast::ast::{Block, Expr, ExprKind, Stmt, StmtKind}; |
| use rustc_ast::visit::{walk_expr, Visitor}; |
| use rustc_lint::{EarlyContext, EarlyLintPass, LintContext}; |
| use rustc_middle::lint::in_external_macro; |
| use rustc_session::declare_lint_pass; |
| |
| declare_clippy_lint! { |
| /// ### What it does |
| /// Checks for `else` blocks that can be removed without changing semantics. |
| /// |
| /// ### Why is this bad? |
| /// The `else` block adds unnecessary indentation and verbosity. |
| /// |
| /// ### Known problems |
| /// Some may prefer to keep the `else` block for clarity. |
| /// |
| /// ### Example |
| /// ```no_run |
| /// fn my_func(count: u32) { |
| /// if count == 0 { |
| /// print!("Nothing to do"); |
| /// return; |
| /// } else { |
| /// print!("Moving on..."); |
| /// } |
| /// } |
| /// ``` |
| /// Use instead: |
| /// ```no_run |
| /// fn my_func(count: u32) { |
| /// if count == 0 { |
| /// print!("Nothing to do"); |
| /// return; |
| /// } |
| /// print!("Moving on..."); |
| /// } |
| /// ``` |
| #[clippy::version = "1.50.0"] |
| pub REDUNDANT_ELSE, |
| pedantic, |
| "`else` branch that can be removed without changing semantics" |
| } |
| |
| declare_lint_pass!(RedundantElse => [REDUNDANT_ELSE]); |
| |
| impl EarlyLintPass for RedundantElse { |
| fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &Stmt) { |
| if in_external_macro(cx.sess(), stmt.span) { |
| return; |
| } |
| // Only look at expressions that are a whole statement |
| let expr: &Expr = match &stmt.kind { |
| StmtKind::Expr(expr) | StmtKind::Semi(expr) => expr, |
| _ => return, |
| }; |
| // if else |
| let (mut then, mut els): (&Block, &Expr) = match &expr.kind { |
| ExprKind::If(_, then, Some(els)) => (then, els), |
| _ => return, |
| }; |
| loop { |
| if !BreakVisitor::default().check_block(then) { |
| // then block does not always break |
| return; |
| } |
| match &els.kind { |
| // else if else |
| ExprKind::If(_, next_then, Some(next_els)) => { |
| then = next_then; |
| els = next_els; |
| continue; |
| }, |
| // else if without else |
| ExprKind::If(..) => return, |
| // done |
| _ => break, |
| } |
| } |
| span_lint_and_help( |
| cx, |
| REDUNDANT_ELSE, |
| els.span, |
| "redundant else block", |
| None, |
| "remove the `else` block and move the contents out", |
| ); |
| } |
| } |
| |
| /// Call `check` functions to check if an expression always breaks control flow |
| #[derive(Default)] |
| struct BreakVisitor { |
| is_break: bool, |
| } |
| |
| impl<'ast> Visitor<'ast> for BreakVisitor { |
| fn visit_block(&mut self, block: &'ast Block) { |
| self.is_break = match block.stmts.as_slice() { |
| [.., last] => self.check_stmt(last), |
| _ => false, |
| }; |
| } |
| |
| fn visit_expr(&mut self, expr: &'ast Expr) { |
| self.is_break = match expr.kind { |
| ExprKind::Break(..) | ExprKind::Continue(..) | ExprKind::Ret(..) => true, |
| ExprKind::Match(_, ref arms) => arms.iter().all(|arm| |
| arm.body.is_none() || arm.body.as_deref().is_some_and(|body| self.check_expr(body)) |
| ), |
| ExprKind::If(_, ref then, Some(ref els)) => self.check_block(then) && self.check_expr(els), |
| ExprKind::If(_, _, None) |
| // ignore loops for simplicity |
| | ExprKind::While(..) | ExprKind::ForLoop { .. } | ExprKind::Loop(..) => false, |
| _ => { |
| walk_expr(self, expr); |
| return; |
| }, |
| }; |
| } |
| } |
| |
| impl BreakVisitor { |
| fn check<T>(&mut self, item: T, visit: fn(&mut Self, T)) -> bool { |
| visit(self, item); |
| std::mem::replace(&mut self.is_break, false) |
| } |
| |
| fn check_block(&mut self, block: &Block) -> bool { |
| self.check(block, Self::visit_block) |
| } |
| |
| fn check_expr(&mut self, expr: &Expr) -> bool { |
| self.check(expr, Self::visit_expr) |
| } |
| |
| fn check_stmt(&mut self, stmt: &Stmt) -> bool { |
| self.check(stmt, Self::visit_stmt) |
| } |
| } |