clippy_lints/src/loops/same_item_push.rs

   1 use super::SAME_ITEM_PUSH;
   2 use clippy_utils::diagnostics::span_lint_and_help;
   3 use clippy_utils::path_to_local;
   4 use clippy_utils::source::snippet_with_macro_callsite;
   5 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
   6 use if_chain::if_chain;
   7 use rustc_data_structures::fx::FxHashSet;
   8 use rustc_hir::def::{DefKind, Res};
   9 use rustc_hir::intravisit::{walk_expr, Visitor};
  10 use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, Node, Pat, PatKind, Stmt, StmtKind};
  11 use rustc_lint::LateContext;
  12 use rustc_span::symbol::sym;
  13 use std::iter::Iterator;
  14
  15 /// Detects for loop pushing the same item into a Vec
  16 pub(super) fn check<'tcx>(
  17     cx: &LateContext<'tcx>,
  18     pat: &'tcx Pat<'_>,
  19     _: &'tcx Expr<'_>,
  20     body: &'tcx Expr<'_>,
  21     _: &'tcx Expr<'_>,
  22 ) {
  23     fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
  24         let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
  25         let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
  26
  27         span_lint_and_help(
  28             cx,
  29             SAME_ITEM_PUSH,
  30             vec.span,
  31             "it looks like the same item is being pushed into this Vec",
  32             None,
  33             &format!(
  34                 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
  35                 item_str, vec_str, item_str
  36             ),
  37         );
  38     }
  39
  40     if !matches!(pat.kind, PatKind::Wild) {
  41         return;
  42     }
  43
  44     // Determine whether it is safe to lint the body
  45     let mut same_item_push_visitor = SameItemPushVisitor::new(cx);
  46     walk_expr(&mut same_item_push_visitor, body);
  47     if_chain! {
  48         if same_item_push_visitor.should_lint();
  49         if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push;
  50         let vec_ty = cx.typeck_results().expr_ty(vec);
  51         let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
  52         if cx
  53             .tcx
  54             .lang_items()
  55             .clone_trait()
  56             .map_or(false, |id| implements_trait(cx, ty, id, &[]));
  57         then {
  58             // Make sure that the push does not involve possibly mutating values
  59             match pushed_item.kind {
  60                 ExprKind::Path(ref qpath) => {
  61                     match cx.qpath_res(qpath, pushed_item.hir_id) {
  62                         // immutable bindings that are initialized with literal or constant
  63                         Res::Local(hir_id) => {
  64                             let node = cx.tcx.hir().get(hir_id);
  65                             if_chain! {
  66                                 if let Node::Pat(pat) = node;
  67                                 if let PatKind::Binding(bind_ann, ..) = pat.kind;
  68                                 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
  69                                 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
  70                                 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
  71                                 if let Some(init) = parent_let_expr.init;
  72                                 then {
  73                                     match init.kind {
  74                                         // immutable bindings that are initialized with literal
  75                                         ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
  76                                         // immutable bindings that are initialized with constant
  77                                         ExprKind::Path(ref path) => {
  78                                             if let Res::Def(DefKind::Const, ..) = cx.qpath_res(path, init.hir_id) {
  79                                                 emit_lint(cx, vec, pushed_item);
  80                                             }
  81                                         }
  82                                         _ => {},
  83                                     }
  84                                 }
  85                             }
  86                         },
  87                         // constant
  88                         Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
  89                         _ => {},
  90                     }
  91                 },
  92                 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
  93                 _ => {},
  94             }
  95         }
  96     }
  97 }
  98
  99 // Scans the body of the for loop and determines whether lint should be given
 100 struct SameItemPushVisitor<'a, 'tcx> {
 101     non_deterministic_expr: bool,
 102     multiple_pushes: bool,
 103     // this field holds the last vec push operation visited, which should be the only push seen
 104     vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
 105     cx: &'a LateContext<'tcx>,
 106     used_locals: FxHashSet<HirId>,
 107 }
 108
 109 impl<'a, 'tcx> SameItemPushVisitor<'a, 'tcx> {
 110     fn new(cx: &'a LateContext<'tcx>) -> Self {
 111         Self {
 112             non_deterministic_expr: false,
 113             multiple_pushes: false,
 114             vec_push: None,
 115             cx,
 116             used_locals: FxHashSet::default(),
 117         }
 118     }
 119
 120     fn should_lint(&self) -> bool {
 121         if_chain! {
 122             if !self.non_deterministic_expr;
 123             if !self.multiple_pushes;
 124             if let Some((vec, _)) = self.vec_push;
 125             if let Some(hir_id) = path_to_local(vec);
 126             then {
 127                 !self.used_locals.contains(&hir_id)
 128             } else {
 129                 false
 130             }
 131         }
 132     }
 133 }
 134
 135 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
 136     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 137         match &expr.kind {
 138             // Non-determinism may occur ... don't give a lint
 139             ExprKind::Loop(..) | ExprKind::Match(..) | ExprKind::If(..) => self.non_deterministic_expr = true,
 140             ExprKind::Block(block, _) => self.visit_block(block),
 141             _ => {
 142                 if let Some(hir_id) = path_to_local(expr) {
 143                     self.used_locals.insert(hir_id);
 144                 }
 145                 walk_expr(self, expr);
 146             },
 147         }
 148     }
 149
 150     fn visit_block(&mut self, b: &'tcx Block<'_>) {
 151         for stmt in b.stmts.iter() {
 152             self.visit_stmt(stmt);
 153         }
 154     }
 155
 156     fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
 157         let vec_push_option = get_vec_push(self.cx, s);
 158         if vec_push_option.is_none() {
 159             // Current statement is not a push so visit inside
 160             match &s.kind {
 161                 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(expr),
 162                 _ => {},
 163             }
 164         } else {
 165             // Current statement is a push ...check whether another
 166             // push had been previously done
 167             if self.vec_push.is_none() {
 168                 self.vec_push = vec_push_option;
 169             } else {
 170                 // There are multiple pushes ... don't lint
 171                 self.multiple_pushes = true;
 172             }
 173         }
 174     }
 175 }
 176
 177 // Given some statement, determine if that statement is a push on a Vec. If it is, return
 178 // the Vec being pushed into and the item being pushed
 179 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
 180     if_chain! {
 181             // Extract method being called
 182             if let StmtKind::Semi(semi_stmt) = &stmt.kind;
 183             if let ExprKind::MethodCall(path, args, _) = &semi_stmt.kind;
 184             // Figure out the parameters for the method call
 185             if let Some(self_expr) = args.get(0);
 186             if let Some(pushed_item) = args.get(1);
 187             // Check that the method being called is push() on a Vec
 188             if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::Vec);
 189             if path.ident.name.as_str() == "push";
 190             then {
 191                 return Some((self_expr, pushed_item))
 192             }
 193     }
 194     None
 195 }