1 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
2 use clippy_utils::get_parent_expr;
3 use clippy_utils::higher;
4 use clippy_utils::source::snippet_block_with_applicability;
5 use clippy_utils::ty::implements_trait;
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::intravisit::{walk_expr, Visitor};
9 use rustc_hir::{BlockCheckMode, Expr, ExprKind};
10 use rustc_lint::{LateContext, LateLintPass, LintContext};
11 use rustc_middle::lint::in_external_macro;
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
15 declare_clippy_lint! {
17 /// Checks for `if` conditions that use blocks containing an
18 /// expression, statements or conditions that use closures with blocks.
20 /// ### Why is this bad?
21 /// Style, using blocks in the condition makes it hard to read.
25 /// # fn somefunc() -> bool { true };
26 /// if { true } { /* ... */ }
28 /// if { let x = somefunc(); x } { /* ... */ }
33 /// # fn somefunc() -> bool { true };
34 /// if true { /* ... */ }
36 /// let res = { let x = somefunc(); x };
37 /// if res { /* ... */ }
39 #[clippy::version = "1.45.0"]
40 pub BLOCKS_IN_IF_CONDITIONS,
42 "useless or complex blocks that can be eliminated in conditions"
45 declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
47 struct ExVisitor<'a, 'tcx> {
48 found_block: Option<&'tcx Expr<'tcx>>,
49 cx: &'a LateContext<'tcx>,
52 impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
53 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
54 if let ExprKind::Closure(_, _, eid, _, _) = expr.kind {
55 // do not lint if the closure is called using an iterator (see #1141)
57 if let Some(parent) = get_parent_expr(self.cx, expr);
58 if let ExprKind::MethodCall(_, [self_arg, ..], _) = &parent.kind;
59 let caller = self.cx.typeck_results().expr_ty(self_arg);
60 if let Some(iter_id) = self.cx.tcx.get_diagnostic_item(sym::Iterator);
61 if implements_trait(self.cx, caller, iter_id, &[]);
67 let body = self.cx.tcx.hir().body(eid);
69 if let ExprKind::Block(block, _) = ex.kind {
70 if !body.value.span.from_expansion() && !block.stmts.is_empty() {
71 self.found_block = Some(ex);
76 walk_expr(self, expr);
80 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
81 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
82 instead, move the block or closure higher and bind it with a `let`";
84 impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
85 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
86 if in_external_macro(cx.sess(), expr.span) {
89 if let Some(higher::If { cond, .. }) = higher::If::hir(expr) {
90 if let ExprKind::Block(block, _) = &cond.kind {
91 if block.rules == BlockCheckMode::DefaultBlock {
92 if block.stmts.is_empty() {
93 if let Some(ex) = &block.expr {
94 // don't dig into the expression here, just suggest that they remove
96 if expr.span.from_expansion() || ex.span.from_expansion() {
99 let mut applicability = Applicability::MachineApplicable;
102 BLOCKS_IN_IF_CONDITIONS,
108 snippet_block_with_applicability(
120 let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
121 if span.from_expansion() || expr.span.from_expansion() {
125 let mut applicability = Applicability::MachineApplicable;
128 BLOCKS_IN_IF_CONDITIONS,
129 expr.span.with_hi(cond.span.hi()),
130 COMPLEX_BLOCK_MESSAGE,
133 "let res = {}; if res",
134 snippet_block_with_applicability(
147 let mut visitor = ExVisitor { found_block: None, cx };
148 walk_expr(&mut visitor, cond);
149 if let Some(block) = visitor.found_block {
150 span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);