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Don't trigger same_item_push if the vec is used in the loop body #7018

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Apr 5, 2021
Merged

Don't trigger same_item_push if the vec is used in the loop body #7018

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137 changes: 84 additions & 53 deletions clippy_lints/src/loops/same_item_push.rs
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Original file line number Diff line number Diff line change
@@ -1,11 +1,13 @@
use super::SAME_ITEM_PUSH;
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::path_to_local;
use clippy_utils::source::snippet_with_macro_callsite;
use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
use if_chain::if_chain;
use rustc_data_structures::fx::FxHashSet;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, Node, Pat, PatKind, Stmt, StmtKind};
use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, Node, Pat, PatKind, Stmt, StmtKind};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_span::symbol::sym;
Expand Down Expand Up @@ -41,70 +43,94 @@ pub(super) fn check<'tcx>(
}

// Determine whether it is safe to lint the body
let mut same_item_push_visitor = SameItemPushVisitor {
should_lint: true,
vec_push: None,
cx,
};
let mut same_item_push_visitor = SameItemPushVisitor::new(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 cx.qpath_res(qpath, pushed_item.hir_id) {
// immutable bindings that are initialized with literal or constant
Res::Local(hir_id) => {
let node = cx.tcx.hir().get(hir_id);
if_chain! {
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, ..) = cx.qpath_res(path, init.hir_id) {
emit_lint(cx, vec, pushed_item);
}
if_chain! {
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, &[]));
then {
// Make sure that the push does not involve possibly mutating values
match pushed_item.kind {
ExprKind::Path(ref qpath) => {
match cx.qpath_res(qpath, pushed_item.hir_id) {
// immutable bindings that are initialized with literal or constant
Res::Local(hir_id) => {
let node = cx.tcx.hir().get(hir_id);
if_chain! {
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, ..) = cx.qpath_res(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),
_ => {},
}
}
},
// constant
Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
_ => {},
}
},
ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
_ => {},
}
}
}
}

// Scans the body of the for loop and determines whether lint should be given
struct SameItemPushVisitor<'a, 'tcx> {
should_lint: bool,
non_deterministic_expr: bool,
multiple_pushes: 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>,
used_locals: FxHashSet<HirId>,
}

impl<'a, 'tcx> SameItemPushVisitor<'a, 'tcx> {
fn new(cx: &'a LateContext<'tcx>) -> Self {
Self {
non_deterministic_expr: false,
multiple_pushes: false,
vec_push: None,
cx,
used_locals: FxHashSet::default(),
}
}

fn should_lint(&self) -> bool {
if_chain! {
if !self.non_deterministic_expr;
if !self.multiple_pushes;
if let Some((vec, _)) = self.vec_push;
if let Some(hir_id) = path_to_local(vec);
then {
!self.used_locals.contains(&hir_id)
} else {
false
}
}
}
}

impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
Expand All @@ -113,9 +139,14 @@ impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, '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::Loop(..) | ExprKind::Match(..) | ExprKind::If(..) => self.non_deterministic_expr = true,
ExprKind::Block(block, _) => self.visit_block(block),
_ => {},
_ => {
if let Some(hir_id) = path_to_local(expr) {
self.used_locals.insert(hir_id);
}
walk_expr(self, expr);
},
}
}

Expand All @@ -140,7 +171,7 @@ impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
self.vec_push = vec_push_option;
} else {
// There are multiple pushes ... don't lint
self.should_lint = false;
self.multiple_pushes = true;
}
}
}
Expand Down
7 changes: 7 additions & 0 deletions tests/ui/same_item_push.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -148,4 +148,11 @@ fn main() {
};
vec.push(item);
}

// Fix #6987
let mut vec = Vec::new();
for _ in 0..10 {
vec.push(1);
vec.extend(&[2]);
}
}