clippy_lints/src/block_in_if_condition.rs

   1 use crate::utils::{differing_macro_contexts, higher, snippet_block_with_applicability, span_lint, span_lint_and_sugg};
   2 use matches::matches;
   3 use rustc::hir::map::Map;
   4 use rustc::lint::in_external_macro;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   7 use rustc_hir::{BlockCheckMode, Expr, ExprKind};
   8 use rustc_lint::{LateContext, LateLintPass, LintContext};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10
  11 declare_clippy_lint! {
  12     /// **What it does:** Checks for `if` conditions that use blocks to contain an
  13     /// expression.
  14     ///
  15     /// **Why is this bad?** It isn't really Rust style, same as using parentheses
  16     /// to contain expressions.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```rust
  22     /// if { true } { /* ... */ }
  23     /// ```
  24     pub BLOCK_IN_IF_CONDITION_EXPR,
  25     style,
  26     "braces that can be eliminated in conditions, e.g., `if { true } ...`"
  27 }
  28
  29 declare_clippy_lint! {
  30     /// **What it does:** Checks for `if` conditions that use blocks containing
  31     /// statements, or conditions that use closures with blocks.
  32     ///
  33     /// **Why is this bad?** Using blocks in the condition makes it hard to read.
  34     ///
  35     /// **Known problems:** None.
  36     ///
  37     /// **Example:**
  38     /// ```ignore
  39     /// if { let x = somefunc(); x } {}
  40     /// // or
  41     /// if somefunc(|x| { x == 47 }) {}
  42     /// ```
  43     pub BLOCK_IN_IF_CONDITION_STMT,
  44     style,
  45     "complex blocks in conditions, e.g., `if { let x = true; x } ...`"
  46 }
  47
  48 declare_lint_pass!(BlockInIfCondition => [BLOCK_IN_IF_CONDITION_EXPR, BLOCK_IN_IF_CONDITION_STMT]);
  49
  50 struct ExVisitor<'a, 'tcx> {
  51     found_block: Option<&'tcx Expr<'tcx>>,
  52     cx: &'a LateContext<'a, 'tcx>,
  53 }
  54
  55 impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
  56     type Map = Map<'tcx>;
  57
  58     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
  59         if let ExprKind::Closure(_, _, eid, _, _) = expr.kind {
  60             let body = self.cx.tcx.hir().body(eid);
  61             let ex = &body.value;
  62             if matches!(ex.kind, ExprKind::Block(_, _)) && !body.value.span.from_expansion() {
  63                 self.found_block = Some(ex);
  64                 return;
  65             }
  66         }
  67         walk_expr(self, expr);
  68     }
  69     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
  70         NestedVisitorMap::None
  71     }
  72 }
  73
  74 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  75 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
  76                                      instead, move the block or closure higher and bind it with a `let`";
  77
  78 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BlockInIfCondition {
  79     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
  80         if in_external_macro(cx.sess(), expr.span) {
  81             return;
  82         }
  83         if let Some((cond, _, _)) = higher::if_block(&expr) {
  84             if let ExprKind::Block(block, _) = &cond.kind {
  85                 if block.rules == BlockCheckMode::DefaultBlock {
  86                     if block.stmts.is_empty() {
  87                         if let Some(ex) = &block.expr {
  88                             // don't dig into the expression here, just suggest that they remove
  89                             // the block
  90                             if expr.span.from_expansion() || differing_macro_contexts(expr.span, ex.span) {
  91                                 return;
  92                             }
  93                             let mut applicability = Applicability::MachineApplicable;
  94                             span_lint_and_sugg(
  95                                 cx,
  96                                 BLOCK_IN_IF_CONDITION_EXPR,
  97                                 cond.span,
  98                                 BRACED_EXPR_MESSAGE,
  99                                 "try",
 100                                 format!(
 101                                     "{}",
 102                                     snippet_block_with_applicability(
 103                                         cx,
 104                                         ex.span,
 105                                         "..",
 106                                         Some(expr.span),
 107                                         &mut applicability
 108                                     )
 109                                 ),
 110                                 applicability,
 111                             );
 112                         }
 113                     } else {
 114                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 115                         if span.from_expansion() || differing_macro_contexts(expr.span, span) {
 116                             return;
 117                         }
 118                         // move block higher
 119                         let mut applicability = Applicability::MachineApplicable;
 120                         span_lint_and_sugg(
 121                             cx,
 122                             BLOCK_IN_IF_CONDITION_STMT,
 123                             expr.span.with_hi(cond.span.hi()),
 124                             COMPLEX_BLOCK_MESSAGE,
 125                             "try",
 126                             format!(
 127                                 "let res = {}; if res",
 128                                 snippet_block_with_applicability(
 129                                     cx,
 130                                     block.span,
 131                                     "..",
 132                                     Some(expr.span),
 133                                     &mut applicability
 134                                 ),
 135                             ),
 136                             applicability,
 137                         );
 138                     }
 139                 }
 140             } else {
 141                 let mut visitor = ExVisitor { found_block: None, cx };
 142                 walk_expr(&mut visitor, cond);
 143                 if let Some(block) = visitor.found_block {
 144                     span_lint(cx, BLOCK_IN_IF_CONDITION_STMT, block.span, COMPLEX_BLOCK_MESSAGE);
 145                 }
 146             }
 147         }
 148     }
 149 }