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 clippy_utils::visitors::{for_each_expr, Descend};
   7 use core::ops::ControlFlow;
   8 use if_chain::if_chain;
   9 use rustc_errors::Applicability;
  10 use rustc_hir::{BlockCheckMode, Expr, ExprKind};
  11 use rustc_lint::{LateContext, LateLintPass, LintContext};
  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     /// # fn somefunc() -> bool { true };
  27     /// if { true } { /* ... */ }
  28     ///
  29     /// if { let x = somefunc(); x } { /* ... */ }
  30     /// ```
  31     ///
  32     /// Use instead:
  33     /// ```rust
  34     /// # fn somefunc() -> bool { true };
  35     /// if true { /* ... */ }
  36     ///
  37     /// let res = { let x = somefunc(); x };
  38     /// if res { /* ... */ }
  39     /// ```
  40     #[clippy::version = "1.45.0"]
  41     pub BLOCKS_IN_IF_CONDITIONS,
  42     style,
  43     "useless or complex blocks that can be eliminated in conditions"
  44 }
  45
  46 declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
  47
  48 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  49 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
  50                                     instead, move the block or closure higher and bind it with a `let`";
  51
  52 impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
  53     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  54         if in_external_macro(cx.sess(), expr.span) {
  55             return;
  56         }
  57         if let Some(higher::If { cond, .. }) = higher::If::hir(expr) {
  58             if let ExprKind::Block(block, _) = &cond.kind {
  59                 if block.rules == BlockCheckMode::DefaultBlock {
  60                     if block.stmts.is_empty() {
  61                         if let Some(ex) = &block.expr {
  62                             // don't dig into the expression here, just suggest that they remove
  63                             // the block
  64                             if expr.span.from_expansion() || ex.span.from_expansion() {
  65                                 return;
  66                             }
  67                             let mut applicability = Applicability::MachineApplicable;
  68                             span_lint_and_sugg(
  69                                 cx,
  70                                 BLOCKS_IN_IF_CONDITIONS,
  71                                 cond.span,
  72                                 BRACED_EXPR_MESSAGE,
  73                                 "try",
  74                                 format!(
  75                                     "{}",
  76                                     snippet_block_with_applicability(
  77                                         cx,
  78                                         ex.span,
  79                                         "..",
  80                                         Some(expr.span),
  81                                         &mut applicability
  82                                     )
  83                                 ),
  84                                 applicability,
  85                             );
  86                         }
  87                     } else {
  88                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
  89                         if span.from_expansion() || expr.span.from_expansion() {
  90                             return;
  91                         }
  92                         // move block higher
  93                         let mut applicability = Applicability::MachineApplicable;
  94                         span_lint_and_sugg(
  95                             cx,
  96                             BLOCKS_IN_IF_CONDITIONS,
  97                             expr.span.with_hi(cond.span.hi()),
  98                             COMPLEX_BLOCK_MESSAGE,
  99                             "try",
 100                             format!(
 101                                 "let res = {}; if res",
 102                                 snippet_block_with_applicability(
 103                                     cx,
 104                                     block.span,
 105                                     "..",
 106                                     Some(expr.span),
 107                                     &mut applicability
 108                                 ),
 109                             ),
 110                             applicability,
 111                         );
 112                     }
 113                 }
 114             } else {
 115                 let _: Option<!> = for_each_expr(cond, |e| {
 116                     if let ExprKind::Closure(closure) = e.kind {
 117                         // do not lint if the closure is called using an iterator (see #1141)
 118                         if_chain! {
 119                             if let Some(parent) = get_parent_expr(cx, e);
 120                             if let ExprKind::MethodCall(_, self_arg, _, _) = &parent.kind;
 121                             let caller = cx.typeck_results().expr_ty(self_arg);
 122                             if let Some(iter_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
 123                             if implements_trait(cx, caller, iter_id, &[]);
 124                             then {
 125                                 return ControlFlow::Continue(Descend::No);
 126                             }
 127                         }
 128
 129                         let body = cx.tcx.hir().body(closure.body);
 130                         let ex = &body.value;
 131                         if let ExprKind::Block(block, _) = ex.kind {
 132                             if !body.value.span.from_expansion() && !block.stmts.is_empty() {
 133                                 span_lint(cx, BLOCKS_IN_IF_CONDITIONS, ex.span, COMPLEX_BLOCK_MESSAGE);
 134                                 return ControlFlow::Continue(Descend::No);
 135                             }
 136                         }
 137                     }
 138                     ControlFlow::Continue(Descend::Yes)
 139                 });
 140             }
 141         }
 142     }
 143 }