src/tools/clippy/clippy_lints/src/blocks_in_if_conditions.rs

   1 use crate::utils::{
   2     differing_macro_contexts, get_parent_expr, get_trait_def_id, implements_trait, paths,
   3     snippet_block_with_applicability, span_lint, span_lint_and_sugg,
   4 };
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   8 use rustc_hir::{BlockCheckMode, Expr, ExprKind};
   9 use rustc_lint::{LateContext, LateLintPass, LintContext};
  10 use rustc_middle::hir::map::Map;
  11 use rustc_middle::lint::in_external_macro;
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for `if` conditions that use blocks containing an
  16     /// expression, statements or conditions that use closures with blocks.
  17     ///
  18     /// **Why is this bad?** Style, using blocks in the condition makes it hard to read.
  19     ///
  20     /// **Known problems:** None.
  21     ///
  22     /// **Examples:**
  23     /// ```rust
  24     /// // Bad
  25     /// if { true } { /* ... */ }
  26     ///
  27     /// // Good
  28     /// if true { /* ... */ }
  29     /// ```
  30     ///
  31     /// // or
  32     ///
  33     /// ```rust
  34     /// # fn somefunc() -> bool { true };
  35     /// // Bad
  36     /// if { let x = somefunc(); x } { /* ... */ }
  37     ///
  38     /// // Good
  39     /// let res = { let x = somefunc(); x };
  40     /// if res { /* ... */ }
  41     /// ```
  42     pub BLOCKS_IN_IF_CONDITIONS,
  43     style,
  44     "useless or complex blocks that can be eliminated in conditions"
  45 }
  46
  47 declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
  48
  49 struct ExVisitor<'a, 'tcx> {
  50     found_block: Option<&'tcx Expr<'tcx>>,
  51     cx: &'a LateContext<'tcx>,
  52 }
  53
  54 impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
  55     type Map = Map<'tcx>;
  56
  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(_, _, args, _) = parent.kind;
  63                 let caller = self.cx.typeck_results().expr_ty(&args[0]);
  64                 if let Some(iter_id) = get_trait_def_id(self.cx, &paths::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 matches!(ex.kind, ExprKind::Block(_, _)) && !body.value.span.from_expansion() {
  74                 self.found_block = Some(ex);
  75                 return;
  76             }
  77         }
  78         walk_expr(self, expr);
  79     }
  80     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
  81         NestedVisitorMap::None
  82     }
  83 }
  84
  85 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  86 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
  87                                     instead, move the block or closure higher and bind it with a `let`";
  88
  89 impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
  90     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  91         if in_external_macro(cx.sess(), expr.span) {
  92             return;
  93         }
  94         if let ExprKind::If(cond, _, _) = &expr.kind {
  95             if let ExprKind::Block(block, _) = &cond.kind {
  96                 if block.rules == BlockCheckMode::DefaultBlock {
  97                     if block.stmts.is_empty() {
  98                         if let Some(ex) = &block.expr {
  99                             // don't dig into the expression here, just suggest that they remove
 100                             // the block
 101                             if expr.span.from_expansion() || differing_macro_contexts(expr.span, ex.span) {
 102                                 return;
 103                             }
 104                             let mut applicability = Applicability::MachineApplicable;
 105                             span_lint_and_sugg(
 106                                 cx,
 107                                 BLOCKS_IN_IF_CONDITIONS,
 108                                 cond.span,
 109                                 BRACED_EXPR_MESSAGE,
 110                                 "try",
 111                                 format!(
 112                                     "{}",
 113                                     snippet_block_with_applicability(
 114                                         cx,
 115                                         ex.span,
 116                                         "..",
 117                                         Some(expr.span),
 118                                         &mut applicability
 119                                     )
 120                                 ),
 121                                 applicability,
 122                             );
 123                         }
 124                     } else {
 125                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 126                         if span.from_expansion() || differing_macro_contexts(expr.span, span) {
 127                             return;
 128                         }
 129                         // move block higher
 130                         let mut applicability = Applicability::MachineApplicable;
 131                         span_lint_and_sugg(
 132                             cx,
 133                             BLOCKS_IN_IF_CONDITIONS,
 134                             expr.span.with_hi(cond.span.hi()),
 135                             COMPLEX_BLOCK_MESSAGE,
 136                             "try",
 137                             format!(
 138                                 "let res = {}; if res",
 139                                 snippet_block_with_applicability(
 140                                     cx,
 141                                     block.span,
 142                                     "..",
 143                                     Some(expr.span),
 144                                     &mut applicability
 145                                 ),
 146                             ),
 147                             applicability,
 148                         );
 149                     }
 150                 }
 151             } else {
 152                 let mut visitor = ExVisitor { found_block: None, cx };
 153                 walk_expr(&mut visitor, cond);
 154                 if let Some(block) = visitor.found_block {
 155                     span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);
 156                 }
 157             }
 158         }
 159     }
 160 }