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