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| 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}; |
| 7 | + |
| 8 | +declare_clippy_lint! { |
| 9 | + /// **What it does:** Checks for `else` blocks that can be removed without changing semantics. |
| 10 | + /// |
| 11 | + /// **Why is this bad?** The `else` block adds unnecessary indentation and verbosity. |
| 12 | + /// |
| 13 | + /// **Known problems:** Some may prefer to keep the `else` block for clarity. |
| 14 | + /// |
| 15 | + /// **Example:** |
| 16 | + /// |
| 17 | + /// ```rust |
| 18 | + /// fn my_func(count: u32) { |
| 19 | + /// if count == 0 { |
| 20 | + /// print!("Nothing to do"); |
| 21 | + /// return; |
| 22 | + /// } else { |
| 23 | + /// print!("Moving on..."); |
| 24 | + /// } |
| 25 | + /// } |
| 26 | + /// ``` |
| 27 | + /// Use instead: |
| 28 | + /// ```rust |
| 29 | + /// fn my_func(count: u32) { |
| 30 | + /// if count == 0 { |
| 31 | + /// print!("Nothing to do"); |
| 32 | + /// return; |
| 33 | + /// } |
| 34 | + /// print!("Moving on..."); |
| 35 | + /// } |
| 36 | + /// ``` |
| 37 | + pub REDUNDANT_ELSE, |
| 38 | + pedantic, |
| 39 | + "`else` branch that can be removed without changing semantics" |
| 40 | +} |
| 41 | + |
| 42 | +declare_lint_pass!(RedundantElse => [REDUNDANT_ELSE]); |
| 43 | + |
| 44 | +impl EarlyLintPass for RedundantElse { |
| 45 | + fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &Stmt) { |
| 46 | + if in_external_macro(cx.sess, stmt.span) { |
| 47 | + return; |
| 48 | + } |
| 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, |
| 52 | + _ => return, |
| 53 | + }; |
| 54 | + // if else |
| 55 | + let (mut then, mut els): (&Block, &Expr) = match &expr.kind { |
| 56 | + ExprKind::If(_, then, Some(els)) => (then, els), |
| 57 | + _ => return, |
| 58 | + }; |
| 59 | + loop { |
| 60 | + if !BreakVisitor::default().check_block(then) { |
| 61 | + // then block does not always break |
| 62 | + return; |
| 63 | + } |
| 64 | + match &els.kind { |
| 65 | + // else if else |
| 66 | + ExprKind::If(_, next_then, Some(next_els)) => { |
| 67 | + then = next_then; |
| 68 | + els = next_els; |
| 69 | + continue; |
| 70 | + }, |
| 71 | + // else if without else |
| 72 | + ExprKind::If(..) => return, |
| 73 | + // done |
| 74 | + _ => break, |
| 75 | + } |
| 76 | + } |
| 77 | + span_lint_and_help( |
| 78 | + cx, |
| 79 | + REDUNDANT_ELSE, |
| 80 | + els.span, |
| 81 | + "redundant else block", |
| 82 | + None, |
| 83 | + "remove the `else` block and move the contents out", |
| 84 | + ); |
| 85 | + } |
| 86 | +} |
| 87 | + |
| 88 | +/// Call `check` functions to check if an expression always breaks control flow |
| 89 | +#[derive(Default)] |
| 90 | +struct BreakVisitor { |
| 91 | + is_break: bool, |
| 92 | +} |
| 93 | + |
| 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), |
| 98 | + _ => false, |
| 99 | + }; |
| 100 | + } |
| 101 | + |
| 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, |
| 110 | + _ => { |
| 111 | + walk_expr(self, expr); |
| 112 | + return; |
| 113 | + }, |
| 114 | + }; |
| 115 | + } |
| 116 | +} |
| 117 | + |
| 118 | +impl BreakVisitor { |
| 119 | + fn check<T>(&mut self, item: T, visit: fn(&mut Self, T)) -> bool { |
| 120 | + visit(self, item); |
| 121 | + std::mem::replace(&mut self.is_break, false) |
| 122 | + } |
| 123 | + |
| 124 | + fn check_block(&mut self, block: &Block) -> bool { |
| 125 | + self.check(block, Self::visit_block) |
| 126 | + } |
| 127 | + |
| 128 | + fn check_expr(&mut self, expr: &Expr) -> bool { |
| 129 | + self.check(expr, Self::visit_expr) |
| 130 | + } |
| 131 | + |
| 132 | + fn check_stmt(&mut self, stmt: &Stmt) -> bool { |
| 133 | + self.check(stmt, Self::visit_stmt) |
| 134 | + } |
| 135 | +} |
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