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