src/misc_early.rs

   1 use rustc::lint::*;
   2 use std::collections::HashMap;
   3 use syntax::ast::*;
   4 use syntax::codemap::Span;
   5 use syntax::visit::FnKind;
   6 use utils::{span_lint, span_help_and_lint, snippet, span_lint_and_then};
   7 /// **What it does:** This lint checks for structure field patterns bound to wildcards.
   8 ///
   9 /// **Why is this bad?** Using `..` instead is shorter and leaves the focus on the fields that are actually bound.
  10 ///
  11 /// **Known problems:** None.
  12 ///
  13 /// **Example:** `let { a: _, b: ref b, c: _ } = ..`
  14 declare_lint! {
  15     pub UNNEEDED_FIELD_PATTERN, Warn,
  16     "Struct fields are bound to a wildcard instead of using `..`"
  17 }
  18
  19 /// **What it does:** This lint checks for function arguments having the similar names differing by an underscore
  20 ///
  21 /// **Why is this bad?** It affects code readability
  22 ///
  23 /// **Known problems:** None.
  24 ///
  25 /// **Example:** `fn foo(a: i32, _a: i32) {}`
  26 declare_lint! {
  27     pub DUPLICATE_UNDERSCORE_ARGUMENT, Warn,
  28     "Function arguments having names which only differ by an underscore"
  29 }
  30
  31 /// **What it does:** This lint detects closures called in the same expression where they are defined.
  32 ///
  33 /// **Why is this bad?** It is unnecessarily adding to the expression's complexity.
  34 ///
  35 /// **Known problems:** None.
  36 ///
  37 /// **Example:** `(|| 42)()`
  38 declare_lint! {
  39     pub REDUNDANT_CLOSURE_CALL, Warn,
  40     "Closures should not be called in the expression they are defined"
  41 }
  42
  43 #[derive(Copy, Clone)]
  44 pub struct MiscEarly;
  45
  46 impl LintPass for MiscEarly {
  47     fn get_lints(&self) -> LintArray {
  48         lint_array!(UNNEEDED_FIELD_PATTERN, DUPLICATE_UNDERSCORE_ARGUMENT, REDUNDANT_CLOSURE_CALL)
  49     }
  50 }
  51
  52 impl EarlyLintPass for MiscEarly {
  53     fn check_pat(&mut self, cx: &EarlyContext, pat: &Pat) {
  54         if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
  55             let mut wilds = 0;
  56             let type_name = npat.segments.last().expect("A path must have at least one segment").identifier.name;
  57
  58             for field in pfields {
  59                 if field.node.pat.node == PatKind::Wild {
  60                     wilds += 1;
  61                 }
  62             }
  63             if !pfields.is_empty() && wilds == pfields.len() {
  64                 span_help_and_lint(cx,
  65                                    UNNEEDED_FIELD_PATTERN,
  66                                    pat.span,
  67                                    "All the struct fields are matched to a wildcard pattern, consider using `..`.",
  68                                    &format!("Try with `{} {{ .. }}` instead", type_name));
  69                 return;
  70             }
  71             if wilds > 0 {
  72                 let mut normal = vec![];
  73
  74                 for field in pfields {
  75                     if field.node.pat.node != PatKind::Wild {
  76                         if let Ok(n) = cx.sess().codemap().span_to_snippet(field.span) {
  77                             normal.push(n);
  78                         }
  79                     }
  80                 }
  81                 for field in pfields {
  82                     if field.node.pat.node == PatKind::Wild {
  83                         wilds -= 1;
  84                         if wilds > 0 {
  85                             span_lint(cx,
  86                                       UNNEEDED_FIELD_PATTERN,
  87                                       field.span,
  88                                       "You matched a field with a wildcard pattern. Consider using `..` instead");
  89                         } else {
  90                             span_help_and_lint(cx,
  91                                                UNNEEDED_FIELD_PATTERN,
  92                                                field.span,
  93                                                "You matched a field with a wildcard pattern. Consider using `..` \
  94                                                 instead",
  95                                                &format!("Try with `{} {{ {}, .. }}`",
  96                                                         type_name,
  97                                                         normal[..].join(", ")));
  98                         }
  99                     }
 100                 }
 101             }
 102         }
 103     }
 104
 105     fn check_fn(&mut self, cx: &EarlyContext, _: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
 106         let mut registered_names: HashMap<String, Span> = HashMap::new();
 107
 108         for ref arg in &decl.inputs {
 109             if let PatKind::Ident(_, sp_ident, None) = arg.pat.node {
 110                 let arg_name = sp_ident.node.to_string();
 111
 112                 if arg_name.starts_with('_') {
 113                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 114                         span_lint(cx,
 115                                   DUPLICATE_UNDERSCORE_ARGUMENT,
 116                                   *correspondence,
 117                                   &format!("`{}` already exists, having another argument having almost the same \
 118                                             name makes code comprehension and documentation more difficult",
 119                                            arg_name[1..].to_owned()));;
 120                     }
 121                 } else {
 122                     registered_names.insert(arg_name, arg.pat.span);
 123                 }
 124             }
 125         }
 126     }
 127
 128     fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
 129         if let ExprKind::Call(ref paren, _) = expr.node {
 130             if let ExprKind::Paren(ref closure) = paren.node {
 131                 if let ExprKind::Closure(_, ref decl, ref block, _) = closure.node {
 132                     span_lint_and_then(cx,
 133                                        REDUNDANT_CLOSURE_CALL,
 134                                        expr.span,
 135                                        "Try not to call a closure in the expression where it is declared.",
 136                                        |db| {
 137                                            if decl.inputs.is_empty() {
 138                                                let hint = format!("{}", snippet(cx, block.span, ".."));
 139                                                db.span_suggestion(expr.span, "Try doing something like: ", hint);
 140                                            }
 141                                        });
 142                 }
 143             }
 144         }
 145     }
 146
 147     fn check_block(&mut self, cx: &EarlyContext, block: &Block) {
 148         for w in block.stmts.windows(2) {
 149             if_let_chain! {[
 150                 let StmtKind::Decl(ref first, _) = w[0].node,
 151                 let DeclKind::Local(ref local) = first.node,
 152                 let Option::Some(ref t) = local.init,
 153                 let ExprKind::Closure(_,_,_,_) = t.node,
 154                 let PatKind::Ident(_,sp_ident,_) = local.pat.node,
 155                 let StmtKind::Semi(ref second,_) = w[1].node,
 156                 let ExprKind::Assign(_,ref call) = second.node,
 157                 let ExprKind::Call(ref closure,_) = call.node,
 158                 let ExprKind::Path(_,ref path) = closure.node
 159             ], {
 160                 if sp_ident.node == (&path.segments[0]).identifier {
 161                     span_lint(cx, REDUNDANT_CLOSURE_CALL, second.span, "Closure called just once immediately after it was declared");
 162                 }
 163             }}
 164         }
 165     }
 166 }