clippy_lints/src/blocks_in_if_conditions.rs

   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, Closure, 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     /// # fn somefunc() -> bool { true };
  26     /// if { true } { /* ... */ }
  27     ///
  28     /// if { let x = somefunc(); x } { /* ... */ }
  29     /// ```
  30     ///
  31     /// Use instead:
  32     /// ```rust
  33     /// # fn somefunc() -> bool { true };
  34     /// if true { /* ... */ }
  35     ///
  36     /// let res = { let x = somefunc(); x };
  37     /// if res { /* ... */ }
  38     /// ```
  39     #[clippy::version = "1.45.0"]
  40     pub BLOCKS_IN_IF_CONDITIONS,
  41     style,
  42     "useless or complex blocks that can be eliminated in conditions"
  43 }
  44
  45 declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
  46
  47 struct ExVisitor<'a, 'tcx> {
  48     found_block: Option<&'tcx Expr<'tcx>>,
  49     cx: &'a LateContext<'tcx>,
  50 }
  51
  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(&Closure { body, .. }) = expr.kind {
  55             // do not lint if the closure is called using an iterator (see #1141)
  56             if_chain! {
  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, &[]);
  62                 then {
  63                     return;
  64                 }
  65             }
  66
  67             let body = self.cx.tcx.hir().body(body);
  68             let ex = &body.value;
  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);
  72                     return;
  73                 }
  74             }
  75         }
  76         walk_expr(self, expr);
  77     }
  78 }
  79
  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`";
  83
  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) {
  87             return;
  88         }
  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
  95                             // the block
  96                             if expr.span.from_expansion() || ex.span.from_expansion() {
  97                                 return;
  98                             }
  99                             let mut applicability = Applicability::MachineApplicable;
 100                             span_lint_and_sugg(
 101                                 cx,
 102                                 BLOCKS_IN_IF_CONDITIONS,
 103                                 cond.span,
 104                                 BRACED_EXPR_MESSAGE,
 105                                 "try",
 106                                 format!(
 107                                     "{}",
 108                                     snippet_block_with_applicability(
 109                                         cx,
 110                                         ex.span,
 111                                         "..",
 112                                         Some(expr.span),
 113                                         &mut applicability
 114                                     )
 115                                 ),
 116                                 applicability,
 117                             );
 118                         }
 119                     } else {
 120                         let span =
 121                             block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 122                         if span.from_expansion() || expr.span.from_expansion() {
 123                             return;
 124                         }
 125                         // move block higher
 126                         let mut applicability = Applicability::MachineApplicable;
 127                         span_lint_and_sugg(
 128                             cx,
 129                             BLOCKS_IN_IF_CONDITIONS,
 130                             expr.span.with_hi(cond.span.hi()),
 131                             COMPLEX_BLOCK_MESSAGE,
 132                             "try",
 133                             format!(
 134                                 "let res = {}; if res",
 135                                 snippet_block_with_applicability(
 136                                     cx,
 137                                     block.span,
 138                                     "..",
 139                                     Some(expr.span),
 140                                     &mut applicability
 141                                 ),
 142                             ),
 143                             applicability,
 144                         );
 145                     }
 146                 }
 147             } else {
 148                 let mut visitor = ExVisitor { found_block: None, cx };
 149                 walk_expr(&mut visitor, cond);
 150                 if let Some(block) = visitor.found_block {
 151                     span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);
 152                 }
 153             }
 154         }
 155     }
 156 }