src/tools/clippy/clippy_lints/src/loops/same_item_push.rs

   1 use super::SAME_ITEM_PUSH;
   2 use crate::utils::{implements_trait, is_type_diagnostic_item, snippet_with_macro_callsite, span_lint_and_help};
   3 use if_chain::if_chain;
   4 use rustc_hir::def::{DefKind, Res};
   5 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   6 use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, Node, Pat, PatKind, Stmt, StmtKind};
   7 use rustc_lint::LateContext;
   8 use rustc_middle::hir::map::Map;
   9 use rustc_span::symbol::sym;
  10 use std::iter::Iterator;
  11
  12 /// Detects for loop pushing the same item into a Vec
  13 pub(super) fn check<'tcx>(
  14     cx: &LateContext<'tcx>,
  15     pat: &'tcx Pat<'_>,
  16     _: &'tcx Expr<'_>,
  17     body: &'tcx Expr<'_>,
  18     _: &'tcx Expr<'_>,
  19 ) {
  20     fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
  21         let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
  22         let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
  23
  24         span_lint_and_help(
  25             cx,
  26             SAME_ITEM_PUSH,
  27             vec.span,
  28             "it looks like the same item is being pushed into this Vec",
  29             None,
  30             &format!(
  31                 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
  32                 item_str, vec_str, item_str
  33             ),
  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 {
  43         should_lint: true,
  44         vec_push: None,
  45         cx,
  46     };
  47     walk_expr(&mut same_item_push_visitor, body);
  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             {
  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                                 if_chain! {
  65                                     let node = cx.tcx.hir().get(hir_id);
  66                                     if let Node::Binding(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
 100 // Scans the body of the for loop and determines whether lint should be given
 101 struct SameItemPushVisitor<'a, 'tcx> {
 102     should_lint: 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 }
 107
 108 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
 109     type Map = Map<'tcx>;
 110
 111     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 112         match &expr.kind {
 113             // Non-determinism may occur ... don't give a lint
 114             ExprKind::Loop(..) | ExprKind::Match(..) => self.should_lint = false,
 115             ExprKind::Block(block, _) => self.visit_block(block),
 116             _ => {},
 117         }
 118     }
 119
 120     fn visit_block(&mut self, b: &'tcx Block<'_>) {
 121         for stmt in b.stmts.iter() {
 122             self.visit_stmt(stmt);
 123         }
 124     }
 125
 126     fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
 127         let vec_push_option = get_vec_push(self.cx, s);
 128         if vec_push_option.is_none() {
 129             // Current statement is not a push so visit inside
 130             match &s.kind {
 131                 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
 132                 _ => {},
 133             }
 134         } else {
 135             // Current statement is a push ...check whether another
 136             // push had been previously done
 137             if self.vec_push.is_none() {
 138                 self.vec_push = vec_push_option;
 139             } else {
 140                 // There are multiple pushes ... don't lint
 141                 self.should_lint = false;
 142             }
 143         }
 144     }
 145
 146     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 147         NestedVisitorMap::None
 148     }
 149 }
 150
 151 // Given some statement, determine if that statement is a push on a Vec. If it is, return
 152 // the Vec being pushed into and the item being pushed
 153 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
 154     if_chain! {
 155             // Extract method being called
 156             if let StmtKind::Semi(semi_stmt) = &stmt.kind;
 157             if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
 158             // Figure out the parameters for the method call
 159             if let Some(self_expr) = args.get(0);
 160             if let Some(pushed_item) = args.get(1);
 161             // Check that the method being called is push() on a Vec
 162             if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::vec_type);
 163             if path.ident.name.as_str() == "push";
 164             then {
 165                 return Some((self_expr, pushed_item))
 166             }
 167     }
 168     None
 169 }