use crate::utils::{
get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
is_integer_const, is_no_std_crate, is_refutable, is_type_diagnostic_item, last_path_segment, match_trait_method,
- match_type, match_var, multispan_sugg, qpath_res, snippet, snippet_opt, snippet_with_applicability, span_lint,
- span_lint_and_help, span_lint_and_sugg, span_lint_and_then, sugg, SpanlessEq,
+ match_type, match_var, multispan_sugg, qpath_res, snippet, snippet_opt, snippet_with_applicability,
+ snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then, sugg,
+ SpanlessEq,
};
use if_chain::if_chain;
use rustc_ast::ast;
"variables used within while expression are not mutated in the body"
}
+declare_clippy_lint! {
+ /// **What it does:** Checks whether a for loop is being used to push a constant
+ /// value into a Vec.
+ ///
+ /// **Why is this bad?** This kind of operation can be expressed more succinctly with
+ /// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also
+ /// have better performance.
+ /// **Known problems:** None
+ ///
+ /// **Example:**
+ /// ```rust
+ /// let item1 = 2;
+ /// let item2 = 3;
+ /// let mut vec: Vec<u8> = Vec::new();
+ /// for _ in 0..20 {
+ /// vec.push(item1);
+ /// }
+ /// for _ in 0..30 {
+ /// vec.push(item2);
+ /// }
+ /// ```
+ /// could be written as
+ /// ```rust
+ /// let item1 = 2;
+ /// let item2 = 3;
+ /// let mut vec: Vec<u8> = vec![item1; 20];
+ /// vec.resize(20 + 30, item2);
+ /// ```
+ pub SAME_ITEM_PUSH,
+ style,
+ "the same item is pushed inside of a for loop"
+}
+
declare_lint_pass!(Loops => [
MANUAL_MEMCPY,
NEEDLESS_RANGE_LOOP,
NEVER_LOOP,
MUT_RANGE_BOUND,
WHILE_IMMUTABLE_CONDITION,
+ SAME_ITEM_PUSH,
]);
impl<'tcx> LateLintPass<'tcx> for Loops {
check_for_loop_over_map_kv(cx, pat, arg, body, expr);
check_for_mut_range_bound(cx, arg, body);
detect_manual_memcpy(cx, pat, arg, body, expr);
+ detect_same_item_push(cx, pat, arg, body, expr);
}
fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
start: Some(start),
end: Some(end),
limits,
- }) = higher::range(cx, arg)
+ }) = higher::range(arg)
{
// the var must be a single name
if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
}
}
+// Scans the body of the for loop and determines whether lint should be given
+struct SameItemPushVisitor<'a, 'tcx> {
+ should_lint: bool,
+ // this field holds the last vec push operation visited, which should be the only push seen
+ vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
+ cx: &'a LateContext<'tcx>,
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
+ type Map = Map<'tcx>;
+
+ fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
+ match &expr.kind {
+ // Non-determinism may occur ... don't give a lint
+ ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
+ ExprKind::Block(block, _) => self.visit_block(block),
+ _ => {},
+ }
+ }
+
+ fn visit_block(&mut self, b: &'tcx Block<'_>) {
+ for stmt in b.stmts.iter() {
+ self.visit_stmt(stmt);
+ }
+ }
+
+ fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
+ let vec_push_option = get_vec_push(self.cx, s);
+ if vec_push_option.is_none() {
+ // Current statement is not a push so visit inside
+ match &s.kind {
+ StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
+ _ => {},
+ }
+ } else {
+ // Current statement is a push ...check whether another
+ // push had been previously done
+ if self.vec_push.is_none() {
+ self.vec_push = vec_push_option;
+ } else {
+ // There are multiple pushes ... don't lint
+ self.should_lint = false;
+ }
+ }
+ }
+
+ fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+ NestedVisitorMap::None
+ }
+}
+
+// Given some statement, determine if that statement is a push on a Vec. If it is, return
+// the Vec being pushed into and the item being pushed
+fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
+ if_chain! {
+ // Extract method being called
+ if let StmtKind::Semi(semi_stmt) = &stmt.kind;
+ if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
+ // Figure out the parameters for the method call
+ if let Some(self_expr) = args.get(0);
+ if let Some(pushed_item) = args.get(1);
+ // Check that the method being called is push() on a Vec
+ if match_type(cx, cx.typeck_results().expr_ty(self_expr), &paths::VEC);
+ if path.ident.name.as_str() == "push";
+ then {
+ return Some((self_expr, pushed_item))
+ }
+ }
+ None
+}
+
+/// Detects for loop pushing the same item into a Vec
+fn detect_same_item_push<'tcx>(
+ cx: &LateContext<'tcx>,
+ pat: &'tcx Pat<'_>,
+ _: &'tcx Expr<'_>,
+ body: &'tcx Expr<'_>,
+ _: &'tcx Expr<'_>,
+) {
+ fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
+ let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
+ let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
+
+ span_lint_and_help(
+ cx,
+ SAME_ITEM_PUSH,
+ vec.span,
+ "it looks like the same item is being pushed into this Vec",
+ None,
+ &format!(
+ "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
+ item_str, vec_str, item_str
+ ),
+ )
+ }
+
+ if !matches!(pat.kind, PatKind::Wild) {
+ return;
+ }
+
+ // Determine whether it is safe to lint the body
+ let mut same_item_push_visitor = SameItemPushVisitor {
+ should_lint: true,
+ vec_push: None,
+ cx,
+ };
+ walk_expr(&mut same_item_push_visitor, body);
+ if same_item_push_visitor.should_lint {
+ if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
+ let vec_ty = cx.typeck_results().expr_ty(vec);
+ let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
+ if cx
+ .tcx
+ .lang_items()
+ .clone_trait()
+ .map_or(false, |id| implements_trait(cx, ty, id, &[]))
+ {
+ // Make sure that the push does not involve possibly mutating values
+ match pushed_item.kind {
+ ExprKind::Path(ref qpath) => {
+ match qpath_res(cx, qpath, pushed_item.hir_id) {
+ // immutable bindings that are initialized with literal or constant
+ Res::Local(hir_id) => {
+ if_chain! {
+ let node = cx.tcx.hir().get(hir_id);
+ if let Node::Binding(pat) = node;
+ if let PatKind::Binding(bind_ann, ..) = pat.kind;
+ if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
+ let parent_node = cx.tcx.hir().get_parent_node(hir_id);
+ if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
+ if let Some(init) = parent_let_expr.init;
+ then {
+ match init.kind {
+ // immutable bindings that are initialized with literal
+ ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
+ // immutable bindings that are initialized with constant
+ ExprKind::Path(ref path) => {
+ if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
+ emit_lint(cx, vec, pushed_item);
+ }
+ }
+ _ => {},
+ }
+ }
+ }
+ },
+ // constant
+ Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
+ _ => {},
+ }
+ },
+ ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
+ _ => {},
+ }
+ }
+ }
+ }
+}
+
/// Checks for looping over a range and then indexing a sequence with it.
/// The iteratee must be a range literal.
#[allow(clippy::too_many_lines)]
start: Some(start),
ref end,
limits,
- }) = higher::range(cx, arg)
+ }) = higher::range(arg)
{
// the var must be a single name
if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
start: Some(start),
end: Some(end),
..
- }) = higher::range(cx, arg)
+ }) = higher::range(arg)
{
let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
if mut_ids[0].is_some() || mut_ids[1].is_some() {
projects / rust.git / blobdiff