clippy_lints/src/blocks_in_if_conditions.rs

   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, 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};
  13 use rustc_span::sym;
  14
  15 declare_clippy_lint! {
  16     /// ### What it does
  17     /// Checks for `if` conditions that use blocks containing an
  18     /// expression, statements or conditions that use closures with blocks.
  19     ///
  20     /// ### Why is this bad?
  21     /// Style, using blocks in the condition makes it hard to read.
  22     ///
  23     /// ### Examples
  24     /// ```rust
  25     /// // Bad
  26     /// if { true } { /* ... */ }
  27     ///
  28     /// // Good
  29     /// if true { /* ... */ }
  30     /// ```
  31     ///
  32     /// // or
  33     ///
  34     /// ```rust
  35     /// # fn somefunc() -> bool { true };
  36     /// // Bad
  37     /// if { let x = somefunc(); x } { /* ... */ }
  38     ///
  39     /// // Good
  40     /// let res = { let x = somefunc(); x };
  41     /// if res { /* ... */ }
  42     /// ```
  43     #[clippy::version = "1.45.0"]
  44     pub BLOCKS_IN_IF_CONDITIONS,
  45     style,
  46     "useless or complex blocks that can be eliminated in conditions"
  47 }
  48
  49 declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
  50
  51 struct ExVisitor<'a, 'tcx> {
  52     found_block: Option<&'tcx Expr<'tcx>>,
  53     cx: &'a LateContext<'tcx>,
  54 }
  55
  56 impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
  57     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
  58         if let ExprKind::Closure(_, _, eid, _, _) = expr.kind {
  59             // do not lint if the closure is called using an iterator (see #1141)
  60             if_chain! {
  61                 if let Some(parent) = get_parent_expr(self.cx, expr);
  62                 if let ExprKind::MethodCall(_, [self_arg, ..], _) = &parent.kind;
  63                 let caller = self.cx.typeck_results().expr_ty(self_arg);
  64                 if let Some(iter_id) = self.cx.tcx.get_diagnostic_item(sym::Iterator);
  65                 if implements_trait(self.cx, caller, iter_id, &[]);
  66                 then {
  67                     return;
  68                 }
  69             }
  70
  71             let body = self.cx.tcx.hir().body(eid);
  72             let ex = &body.value;
  73             if let ExprKind::Block(block, _) = ex.kind {
  74                 if !body.value.span.from_expansion() && !block.stmts.is_empty() {
  75                     self.found_block = Some(ex);
  76                     return;
  77                 }
  78             }
  79         }
  80         walk_expr(self, expr);
  81     }
  82 }
  83
  84 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  85 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
  86                                     instead, move the block or closure higher and bind it with a `let`";
  87
  88 impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
  89     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  90         if in_external_macro(cx.sess(), expr.span) {
  91             return;
  92         }
  93         if let Some(higher::If { cond, .. }) = higher::If::hir(expr) {
  94             if let ExprKind::Block(block, _) = &cond.kind {
  95                 if block.rules == BlockCheckMode::DefaultBlock {
  96                     if block.stmts.is_empty() {
  97                         if let Some(ex) = &block.expr {
  98                             // don't dig into the expression here, just suggest that they remove
  99                             // the block
 100                             if expr.span.from_expansion() || differing_macro_contexts(expr.span, ex.span) {
 101                                 return;
 102                             }
 103                             let mut applicability = Applicability::MachineApplicable;
 104                             span_lint_and_sugg(
 105                                 cx,
 106                                 BLOCKS_IN_IF_CONDITIONS,
 107                                 cond.span,
 108                                 BRACED_EXPR_MESSAGE,
 109                                 "try",
 110                                 format!(
 111                                     "{}",
 112                                     snippet_block_with_applicability(
 113                                         cx,
 114                                         ex.span,
 115                                         "..",
 116                                         Some(expr.span),
 117                                         &mut applicability
 118                                     )
 119                                 ),
 120                                 applicability,
 121                             );
 122                         }
 123                     } else {
 124                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 125                         if span.from_expansion() || differing_macro_contexts(expr.span, span) {
 126                             return;
 127                         }
 128                         // move block higher
 129                         let mut applicability = Applicability::MachineApplicable;
 130                         span_lint_and_sugg(
 131                             cx,
 132                             BLOCKS_IN_IF_CONDITIONS,
 133                             expr.span.with_hi(cond.span.hi()),
 134                             COMPLEX_BLOCK_MESSAGE,
 135                             "try",
 136                             format!(
 137                                 "let res = {}; if res",
 138                                 snippet_block_with_applicability(
 139                                     cx,
 140                                     block.span,
 141                                     "..",
 142                                     Some(expr.span),
 143                                     &mut applicability
 144                                 ),
 145                             ),
 146                             applicability,
 147                         );
 148                     }
 149                 }
 150             } else {
 151                 let mut visitor = ExVisitor { found_block: None, cx };
 152                 walk_expr(&mut visitor, cond);
 153                 if let Some(block) = visitor.found_block {
 154                     span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);
 155                 }
 156             }
 157         }
 158     }
 159 }