src/block_in_if_condition.rs

   1 use rustc::lint::{LateLintPass, LateContext, LintArray, LintPass};
   2 use rustc::hir::*;
   3 use rustc::hir::intravisit::{Visitor, walk_expr};
   4 use utils::*;
   5
   6 /// **What it does:** This lint checks for `if` conditions that use blocks to contain an expression.
   7 ///
   8 /// **Why is this bad?** It isn't really rust style, same as using parentheses to contain expressions.
   9 ///
  10 /// **Known problems:** None
  11 ///
  12 /// **Example:** `if { true } ..`
  13 declare_lint! {
  14     pub BLOCK_IN_IF_CONDITION_EXPR, Warn,
  15     "braces can be eliminated in conditions that are expressions, e.g `if { true } ...`"
  16 }
  17
  18 /// **What it does:** This lint checks for `if` conditions that use blocks containing statements, or conditions that use closures with blocks.
  19 ///
  20 /// **Why is this bad?** Using blocks in the condition makes it hard to read.
  21 ///
  22 /// **Known problems:** None
  23 ///
  24 /// **Example:** `if { let x = somefunc(); x } ..` or `if somefunc(|x| { x == 47 }) ..`
  25 declare_lint! {
  26     pub BLOCK_IN_IF_CONDITION_STMT, Warn,
  27     "avoid complex blocks in conditions, instead move the block higher and bind it \
  28     with 'let'; e.g: `if { let x = true; x } ...`"
  29 }
  30
  31 #[derive(Copy,Clone)]
  32 pub struct BlockInIfCondition;
  33
  34 impl LintPass for BlockInIfCondition {
  35     fn get_lints(&self) -> LintArray {
  36         lint_array!(BLOCK_IN_IF_CONDITION_EXPR, BLOCK_IN_IF_CONDITION_STMT)
  37     }
  38 }
  39
  40 struct ExVisitor<'v> {
  41     found_block: Option<&'v Expr>,
  42 }
  43
  44 impl<'v> Visitor<'v> for ExVisitor<'v> {
  45     fn visit_expr(&mut self, expr: &'v Expr) {
  46         if let ExprClosure(_, _, ref block, _) = expr.node {
  47             let complex = {
  48                 if block.stmts.is_empty() {
  49                     if let Some(ref ex) = block.expr {
  50                         match ex.node {
  51                             ExprBlock(_) => true,
  52                             _ => false,
  53                         }
  54                     } else {
  55                         false
  56                     }
  57                 } else {
  58                     true
  59                 }
  60             };
  61             if complex {
  62                 self.found_block = Some(&expr);
  63                 return;
  64             }
  65         }
  66         walk_expr(self, expr);
  67     }
  68 }
  69
  70 const BRACED_EXPR_MESSAGE: &'static str = "omit braces around single expression condition";
  71 const COMPLEX_BLOCK_MESSAGE: &'static str = "in an 'if' condition, avoid complex blocks or closures with blocks; \
  72                                              instead, move the block or closure higher and bind it with a 'let'";
  73
  74 impl LateLintPass for BlockInIfCondition {
  75     fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
  76         if let ExprIf(ref check, ref then, _) = expr.node {
  77             if let ExprBlock(ref block) = check.node {
  78                 if block.rules == DefaultBlock {
  79                     if block.stmts.is_empty() {
  80                         if let Some(ref ex) = block.expr {
  81                             // don't dig into the expression here, just suggest that they remove
  82                             // the block
  83                             if in_macro(cx, expr.span) || differing_macro_contexts(expr.span, ex.span) {
  84                                 return;
  85                             }
  86                             span_help_and_lint(cx,
  87                                                BLOCK_IN_IF_CONDITION_EXPR,
  88                                                check.span,
  89                                                BRACED_EXPR_MESSAGE,
  90                                                &format!("try\nif {} {} ... ",
  91                                                         snippet_block(cx, ex.span, ".."),
  92                                                         snippet_block(cx, then.span, "..")));
  93                         }
  94                     } else {
  95                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
  96                         if in_macro(cx, span) || differing_macro_contexts(expr.span, span) {
  97                             return;
  98                         }
  99                         // move block higher
 100                         span_help_and_lint(cx,
 101                                            BLOCK_IN_IF_CONDITION_STMT,
 102                                            check.span,
 103                                            COMPLEX_BLOCK_MESSAGE,
 104                                            &format!("try\nlet res = {};\nif res {} ... ",
 105                                                     snippet_block(cx, block.span, ".."),
 106                                                     snippet_block(cx, then.span, "..")));
 107                     }
 108                 }
 109             } else {
 110                 let mut visitor = ExVisitor { found_block: None };
 111                 walk_expr(&mut visitor, check);
 112                 if let Some(ref block) = visitor.found_block {
 113                     span_help_and_lint(cx, BLOCK_IN_IF_CONDITION_STMT, block.span, COMPLEX_BLOCK_MESSAGE, "");
 114                 }
 115             }
 116         }
 117     }
 118 }