79 lines
2.9 KiB
Rust
79 lines
2.9 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::higher::If;
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use clippy_utils::is_from_proc_macro;
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use clippy_utils::source::snippet_opt;
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use rustc_errors::Applicability;
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use rustc_hir::{ExprKind, Stmt, StmtKind};
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use rustc_lint::{LateContext, LateLintPass, 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 empty `if` branches with no else branch.
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///
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/// ### Why is this bad?
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/// It can be entirely omitted, and often the condition too.
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///
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/// ### Known issues
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/// This will usually only suggest to remove the `if` statement, not the condition. Other lints
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/// such as `no_effect` will take care of removing the condition if it's unnecessary.
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///
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/// ### Example
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/// ```rust,ignore
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/// if really_expensive_condition(&i) {}
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/// if really_expensive_condition_with_side_effects(&mut i) {}
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/// ```
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/// Use instead:
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/// ```rust,ignore
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/// // <omitted>
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/// really_expensive_condition_with_side_effects(&mut i);
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/// ```
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#[clippy::version = "1.72.0"]
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pub NEEDLESS_IF,
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complexity,
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"checks for empty if branches"
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}
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declare_lint_pass!(NeedlessIf => [NEEDLESS_IF]);
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impl LateLintPass<'_> for NeedlessIf {
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fn check_stmt<'tcx>(&mut self, cx: &LateContext<'tcx>, stmt: &Stmt<'tcx>) {
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if let StmtKind::Expr(expr) = stmt.kind
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&& let Some(If {cond, then, r#else: None }) = If::hir(expr)
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&& let ExprKind::Block(block, ..) = then.kind
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&& block.stmts.is_empty()
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&& block.expr.is_none()
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&& !in_external_macro(cx.sess(), expr.span)
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&& let Some(then_snippet) = snippet_opt(cx, then.span)
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// Ignore
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// - empty macro expansions
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// - empty reptitions in macro expansions
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// - comments
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// - #[cfg]'d out code
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&& then_snippet.chars().all(|ch| matches!(ch, '{' | '}') || ch.is_ascii_whitespace())
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&& let Some(cond_snippet) = snippet_opt(cx, cond.span)
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&& !is_from_proc_macro(cx, expr)
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{
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span_lint_and_sugg(
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cx,
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NEEDLESS_IF,
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stmt.span,
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"this `if` branch is empty",
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"you can remove it",
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if cond.can_have_side_effects() || !cx.tcx.hir().attrs(stmt.hir_id).is_empty() {
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// `{ foo }` or `{ foo } && bar` placed into a statement position would be
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// interpreted as a block statement, force it to be an expression
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if cond_snippet.starts_with('{') {
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format!("({cond_snippet});")
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} else {
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format!("{cond_snippet};")
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}
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} else {
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String::new()
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},
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Applicability::MachineApplicable,
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);
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}
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}
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}
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