1 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
2 use clippy_utils::higher;
3 use clippy_utils::source::snippet_block_with_applicability;
4 use clippy_utils::ty::implements_trait;
5 use clippy_utils::{differing_macro_contexts, get_parent_expr};
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
9 use rustc_hir::{BlockCheckMode, Expr, ExprKind};
10 use rustc_lint::{LateContext, LateLintPass, LintContext};
11 use rustc_middle::hir::map::Map;
12 use rustc_middle::lint::in_external_macro;
13 use rustc_session::{declare_lint_pass, declare_tool_lint};
16 declare_clippy_lint! {
18 /// Checks for `if` conditions that use blocks containing an
19 /// expression, statements or conditions that use closures with blocks.
21 /// ### Why is this bad?
22 /// Style, using blocks in the condition makes it hard to read.
27 /// if { true } { /* ... */ }
30 /// if true { /* ... */ }
36 /// # fn somefunc() -> bool { true };
38 /// if { let x = somefunc(); x } { /* ... */ }
41 /// let res = { let x = somefunc(); x };
42 /// if res { /* ... */ }
44 pub BLOCKS_IN_IF_CONDITIONS,
46 "useless or complex blocks that can be eliminated in conditions"
49 declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
51 struct ExVisitor<'a, 'tcx> {
52 found_block: Option<&'tcx Expr<'tcx>>,
53 cx: &'a LateContext<'tcx>,
56 impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
59 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
60 if let ExprKind::Closure(_, _, eid, _, _) = expr.kind {
61 // do not lint if the closure is called using an iterator (see #1141)
63 if let Some(parent) = get_parent_expr(self.cx, expr);
64 if let ExprKind::MethodCall(_, _, [self_arg, ..], _) = &parent.kind;
65 let caller = self.cx.typeck_results().expr_ty(self_arg);
66 if let Some(iter_id) = self.cx.tcx.get_diagnostic_item(sym::Iterator);
67 if implements_trait(self.cx, caller, iter_id, &[]);
73 let body = self.cx.tcx.hir().body(eid);
75 if matches!(ex.kind, ExprKind::Block(_, _)) && !body.value.span.from_expansion() {
76 self.found_block = Some(ex);
80 walk_expr(self, expr);
82 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
83 NestedVisitorMap::None
87 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
88 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
89 instead, move the block or closure higher and bind it with a `let`";
91 impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
92 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
93 if in_external_macro(cx.sess(), expr.span) {
96 if let Some(higher::If { cond, .. }) = higher::If::hir(expr) {
97 if let ExprKind::Block(block, _) = &cond.kind {
98 if block.rules == BlockCheckMode::DefaultBlock {
99 if block.stmts.is_empty() {
100 if let Some(ex) = &block.expr {
101 // don't dig into the expression here, just suggest that they remove
103 if expr.span.from_expansion() || differing_macro_contexts(expr.span, ex.span) {
106 let mut applicability = Applicability::MachineApplicable;
109 BLOCKS_IN_IF_CONDITIONS,
115 snippet_block_with_applicability(
127 let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
128 if span.from_expansion() || differing_macro_contexts(expr.span, span) {
132 let mut applicability = Applicability::MachineApplicable;
135 BLOCKS_IN_IF_CONDITIONS,
136 expr.span.with_hi(cond.span.hi()),
137 COMPLEX_BLOCK_MESSAGE,
140 "let res = {}; if res",
141 snippet_block_with_applicability(
154 let mut visitor = ExVisitor { found_block: None, cx };
155 walk_expr(&mut visitor, cond);
156 if let Some(block) = visitor.found_block {
157 span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);