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, 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};
  14 use rustc_span::sym;
  15
  16 declare_clippy_lint! {
  17     /// ### What it does
  18     /// Checks for `if` conditions that use blocks containing an
  19     /// expression, statements or conditions that use closures with blocks.
  20     ///
  21     /// ### Why is this bad?
  22     /// Style, using blocks in the condition makes it hard to read.
  23     ///
  24     /// ### Examples
  25     /// ```rust
  26     /// // Bad
  27     /// if { true } { /* ... */ }
  28     ///
  29     /// // Good
  30     /// if true { /* ... */ }
  31     /// ```
  32     ///
  33     /// // or
  34     ///
  35     /// ```rust
  36     /// # fn somefunc() -> bool { true };
  37     /// // Bad
  38     /// if { let x = somefunc(); x } { /* ... */ }
  39     ///
  40     /// // Good
  41     /// let res = { let x = somefunc(); x };
  42     /// if res { /* ... */ }
  43     /// ```
  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     type Map = Map<'tcx>;
  58
  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)
  62             if_chain! {
  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, &[]);
  68                 then {
  69                     return;
  70                 }
  71             }
  72
  73             let body = self.cx.tcx.hir().body(eid);
  74             let ex = &body.value;
  75             if let ExprKind::Block(block, _) = ex.kind {
  76                 if !body.value.span.from_expansion() && !block.stmts.is_empty() {
  77                     self.found_block = Some(ex);
  78                     return;
  79                 }
  80             }
  81         }
  82         walk_expr(self, expr);
  83     }
  84     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
  85         NestedVisitorMap::None
  86     }
  87 }
  88
  89 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  90 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
  91                                     instead, move the block or closure higher and bind it with a `let`";
  92
  93 impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
  94     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  95         if in_external_macro(cx.sess(), expr.span) {
  96             return;
  97         }
  98         if let Some(higher::If { cond, .. }) = higher::If::hir(expr) {
  99             if let ExprKind::Block(block, _) = &cond.kind {
 100                 if block.rules == BlockCheckMode::DefaultBlock {
 101                     if block.stmts.is_empty() {
 102                         if let Some(ex) = &block.expr {
 103                             // don't dig into the expression here, just suggest that they remove
 104                             // the block
 105                             if expr.span.from_expansion() || differing_macro_contexts(expr.span, ex.span) {
 106                                 return;
 107                             }
 108                             let mut applicability = Applicability::MachineApplicable;
 109                             span_lint_and_sugg(
 110                                 cx,
 111                                 BLOCKS_IN_IF_CONDITIONS,
 112                                 cond.span,
 113                                 BRACED_EXPR_MESSAGE,
 114                                 "try",
 115                                 format!(
 116                                     "{}",
 117                                     snippet_block_with_applicability(
 118                                         cx,
 119                                         ex.span,
 120                                         "..",
 121                                         Some(expr.span),
 122                                         &mut applicability
 123                                     )
 124                                 ),
 125                                 applicability,
 126                             );
 127                         }
 128                     } else {
 129                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 130                         if span.from_expansion() || differing_macro_contexts(expr.span, span) {
 131                             return;
 132                         }
 133                         // move block higher
 134                         let mut applicability = Applicability::MachineApplicable;
 135                         span_lint_and_sugg(
 136                             cx,
 137                             BLOCKS_IN_IF_CONDITIONS,
 138                             expr.span.with_hi(cond.span.hi()),
 139                             COMPLEX_BLOCK_MESSAGE,
 140                             "try",
 141                             format!(
 142                                 "let res = {}; if res",
 143                                 snippet_block_with_applicability(
 144                                     cx,
 145                                     block.span,
 146                                     "..",
 147                                     Some(expr.span),
 148                                     &mut applicability
 149                                 ),
 150                             ),
 151                             applicability,
 152                         );
 153                     }
 154                 }
 155             } else {
 156                 let mut visitor = ExVisitor { found_block: None, cx };
 157                 walk_expr(&mut visitor, cond);
 158                 if let Some(block) = visitor.found_block {
 159                     span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);
 160                 }
 161             }
 162         }
 163     }
 164 }