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new lint: unnecessary_reserve
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‎CHANGELOG.md‎

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@@ -6173,6 +6173,7 @@ Released 2018-09-13
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[`unnecessary_mut_passed`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_mut_passed
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[`unnecessary_operation`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_operation
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[`unnecessary_owned_empty_strings`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_owned_empty_strings
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[`unnecessary_reserve`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_reserve
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[`unnecessary_result_map_or_else`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_result_map_or_else
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[`unnecessary_safety_comment`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_safety_comment
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[`unnecessary_safety_doc`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_safety_doc

‎clippy_lints/src/declared_lints.rs‎

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@@ -624,6 +624,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
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crate::pathbuf_init_then_push::PATHBUF_INIT_THEN_PUSH_INFO,
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crate::pattern_type_mismatch::PATTERN_TYPE_MISMATCH_INFO,
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crate::permissions_set_readonly_false::PERMISSIONS_SET_READONLY_FALSE_INFO,
627+
crate::unnecessary_reserve::UNNECESSARY_RESERVE_INFO,
627628
crate::pointers_in_nomem_asm_block::POINTERS_IN_NOMEM_ASM_BLOCK_INFO,
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crate::precedence::PRECEDENCE_INFO,
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crate::ptr::CMP_NULL_INFO,

‎clippy_lints/src/lib.rs‎

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@@ -372,6 +372,7 @@ mod unnecessary_box_returns;
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mod unnecessary_literal_bound;
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mod unnecessary_map_on_constructor;
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mod unnecessary_owned_empty_strings;
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mod unnecessary_reserve;
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mod unnecessary_self_imports;
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mod unnecessary_semicolon;
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mod unnecessary_struct_initialization;
@@ -956,6 +957,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
956957
store.register_late_pass(move |_| Box::new(assigning_clones::AssigningClones::new(conf)));
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store.register_late_pass(|_| Box::new(zero_repeat_side_effects::ZeroRepeatSideEffects));
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store.register_late_pass(|_| Box::new(manual_unwrap_or_default::ManualUnwrapOrDefault));
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store.register_late_pass(move |_| Box::new(unnecessary_reserve::UnnecessaryReserve::new(conf)));
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store.register_late_pass(|_| Box::new(integer_division_remainder_used::IntegerDivisionRemainderUsed));
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store.register_late_pass(move |_| Box::new(macro_metavars_in_unsafe::ExprMetavarsInUnsafe::new(conf)));
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store.register_late_pass(move |_| Box::new(string_patterns::StringPatterns::new(conf)));

‎clippy_lints/src/unnecessary_reserve.rs‎

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@@ -0,0 +1,129 @@
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use clippy_config::Conf;
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use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::msrvs::{self, Msrv};
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use clippy_utils::visitors::for_each_expr;
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use clippy_utils::{SpanlessEq, get_enclosing_block, match_def_path, paths};
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use core::ops::ControlFlow;
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use rustc_errors::Applicability;
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use rustc_hir::{Block, Expr, ExprKind, PathSegment};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_session::impl_lint_pass;
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use rustc_span::sym;
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declare_clippy_lint! {
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/// ### What it does
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///
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/// This lint checks for a call to `reserve` before `extend` on a `Vec` or `VecDeque`.
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/// ### Why is this bad?
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/// Since Rust 1.62, `extend` implicitly calls `reserve`
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///
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/// ### Example
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/// ```rust
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/// let mut vec: Vec<usize> = vec![];
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/// let array: &[usize] = &[1, 2];
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/// vec.reserve(array.len());
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/// vec.extend(array);
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/// ```
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/// Use instead:
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/// ```rust
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/// let mut vec: Vec<usize> = vec![];
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/// let array: &[usize] = &[1, 2];
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/// vec.extend(array);
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/// ```
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#[clippy::version = "1.64.0"]
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pub UNNECESSARY_RESERVE,
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pedantic,
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"calling `reserve` before `extend` on a `Vec` or `VecDeque`, when it will be called implicitly"
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}
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impl_lint_pass!(UnnecessaryReserve => [UNNECESSARY_RESERVE]);
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pub struct UnnecessaryReserve {
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msrv: Msrv,
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}
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impl UnnecessaryReserve {
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pub fn new(conf: &'static Conf) -> Self {
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Self {
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msrv: conf.msrv.clone(),
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}
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}
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}
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impl<'tcx> LateLintPass<'tcx> for UnnecessaryReserve {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
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if !self.msrv.meets(msrvs::EXTEND_IMPLICIT_RESERVE) {
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return;
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}
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if let ExprKind::MethodCall(PathSegment { ident: method, .. }, struct_calling_on, args_a, _) = expr.kind
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&& method.name.as_str() == "reserve"
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&& acceptable_type(cx, struct_calling_on)
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&& let Some(block) = get_enclosing_block(cx, expr.hir_id)
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&& let Some(next_stmt_span) = check_extend_method(cx, block, struct_calling_on, &args_a[0])
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&& !next_stmt_span.from_expansion()
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{
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span_lint_and_then(
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cx,
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UNNECESSARY_RESERVE,
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next_stmt_span,
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"unnecessary call to `reserve`",
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|diag| {
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diag.span_suggestion(
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expr.span,
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"remove this line",
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String::new(),
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Applicability::MaybeIncorrect,
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);
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},
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);
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}
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}
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extract_msrv_attr!(LateContext);
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}
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#[must_use]
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fn acceptable_type<'tcx>(cx: &LateContext<'tcx>, struct_calling_on: &Expr<'_>) -> bool {
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let acceptable_types = [sym::Vec, sym::VecDeque];
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acceptable_types.iter().any(|&acceptable_ty| {
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match cx.typeck_results().expr_ty(struct_calling_on).peel_refs().kind() {
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ty::Adt(def, _) => cx.tcx.is_diagnostic_item(acceptable_ty, def.did()),
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_ => false,
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}
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})
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}
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#[must_use]
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fn check_extend_method<'tcx>(
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cx: &LateContext<'tcx>,
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block: &'tcx Block<'tcx>,
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struct_expr: &Expr<'tcx>,
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args_a: &Expr<'tcx>,
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) -> Option<rustc_span::Span> {
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let args_a_kind = &args_a.kind;
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let mut read_found = false;
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let mut spanless_eq = SpanlessEq::new(cx);
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let _: Option<!> = for_each_expr(cx, block, |expr: &Expr<'tcx>| {
109+
if let ExprKind::MethodCall(_, struct_calling_on, _, _) = expr.kind
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&& let Some(expr_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
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&& let ExprKind::MethodCall(
112+
PathSegment {
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ident: method_call_a, ..
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},
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..,
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) = args_a_kind
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&& method_call_a.name == sym::len
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&& match_def_path(cx, expr_def_id, &paths::ITER_EXTEND)
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&& acceptable_type(cx, struct_calling_on)
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&& spanless_eq.eq_expr(struct_calling_on, struct_expr)
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{
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read_found = true;
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}
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let _: bool = !read_found;
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ControlFlow::Continue(())
126+
});
127+
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if read_found { Some(block.span) } else { None }
129+
}

‎clippy_utils/src/msrvs.rs‎

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@@ -31,7 +31,7 @@ msrv_aliases! {
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1,68,0 { PATH_MAIN_SEPARATOR_STR }
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1,65,0 { LET_ELSE, POINTER_CAST_CONSTNESS }
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1,63,0 { CLONE_INTO }
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1,62,0 { BOOL_THEN_SOME, DEFAULT_ENUM_ATTRIBUTE, CONST_EXTERN_C_FN }
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1,62,0 { BOOL_THEN_SOME, DEFAULT_ENUM_ATTRIBUTE, CONST_EXTERN_C_FN, EXTEND_IMPLICIT_RESERVE }
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1,59,0 { THREAD_LOCAL_CONST_INIT }
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1,58,0 { FORMAT_ARGS_CAPTURE, PATTERN_TRAIT_CHAR_ARRAY, CONST_RAW_PTR_DEREF }
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1,56,0 { CONST_FN_UNION }

‎clippy_utils/src/paths.rs‎

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@@ -15,6 +15,7 @@ pub const APPLICABILITY_VALUES: [[&str; 3]; 4] = [
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pub const DIAG: [&str; 2] = ["rustc_errors", "Diag"];
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pub const EARLY_CONTEXT: [&str; 2] = ["rustc_lint", "EarlyContext"];
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pub const EARLY_LINT_PASS: [&str; 3] = ["rustc_lint", "passes", "EarlyLintPass"];
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pub const ITER_EXTEND: [&str; 6] = ["core", "iter", "traits", "collect", "Extend", "extend"];
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pub const IDENT: [&str; 3] = ["rustc_span", "symbol", "Ident"];
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pub const IDENT_AS_STR: [&str; 4] = ["rustc_span", "symbol", "Ident", "as_str"];
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pub const KW_MODULE: [&str; 3] = ["rustc_span", "symbol", "kw"];

‎tests/ui/unnecessary_reserve.fixed‎

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@@ -0,0 +1,99 @@
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#![warn(clippy::unnecessary_reserve)]
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#![feature(custom_inner_attributes)]
3+
4+
#![allow(clippy::unnecessary_operation)]
5+
use std::collections::{HashMap, VecDeque};
6+
7+
fn main() {
8+
vec_reserve();
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vec_deque_reserve();
10+
hash_map_reserve();
11+
msrv_1_62();
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}
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fn vec_reserve() {
15+
let mut vec: Vec<usize> = vec![];
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let array1: &[usize] = &[1, 2];
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let array2: &[usize] = &[3, 4];
18+
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// do not lint - different arrays
20+
;
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vec.extend(array2);
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// do not lint
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vec.reserve(1);
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vec.extend([1]);
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//// do lint
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;
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vec.extend(array1);
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// do lint
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{
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;
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vec.extend(array1)
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};
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// do not lint
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;
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vec.push(1);
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vec.extend(array1);
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// do not lint
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let mut other_vec: Vec<usize> = Vec::with_capacity(1);
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vec.extend([1])
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}
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fn vec_deque_reserve() {
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let mut vec_deque: VecDeque<usize> = [1].into();
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let array: &[usize] = &[1, 2];
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// do not lint
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vec_deque.reserve(1);
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vec_deque.extend([1]);
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// do lint
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;
57+
vec_deque.extend(array);
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// do not lint
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{
61+
vec_deque.reserve(1);
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vec_deque.extend([1])
63+
};
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// do not lint
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vec_deque.reserve(array.len() + 1);
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vec_deque.push_back(1);
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vec_deque.extend(array);
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// do not lint
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let mut other_vec_deque: VecDeque<usize> = [1].into();
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other_vec_deque.reserve(1);
73+
vec_deque.extend([1])
74+
}
75+
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fn hash_map_reserve() {
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let mut map: HashMap<usize, usize> = HashMap::new();
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let mut other_map: HashMap<usize, usize> = HashMap::new();
79+
// do not lint
80+
map.reserve(other_map.len());
81+
map.extend(other_map);
82+
}
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fn msrv_1_62() {
85+
#![clippy::msrv = "1.61"]
86+
let mut vec: Vec<usize> = vec![];
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let array: &[usize] = &[1, 2];
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// do not lint
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vec.reserve(1);
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vec.extend([1]);
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93+
let mut vec_deque: VecDeque<usize> = [1].into();
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let array: &[usize] = &[1, 2];
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// do not lint
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vec_deque.reserve(1);
98+
vec_deque.extend([1]);
99+
}

‎tests/ui/unnecessary_reserve.rs‎

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@@ -0,0 +1,100 @@
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#![warn(clippy::unnecessary_reserve)]
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#![feature(custom_inner_attributes)]
3+
4+
#[allow(clippy::unnecessary_operation)]
5+
use std::collections::{HashMap, VecDeque};
6+
7+
fn main() {
8+
vec_reserve();
9+
vec_deque_reserve();
10+
hash_map_reserve();
11+
msrv_1_62();
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}
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fn vec_reserve() {
15+
let mut vec: Vec<usize> = vec![];
16+
let array1: &[usize] = &[1, 2];
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let array2: &[usize] = &[3, 4];
18+
19+
// do not lint - different arrays
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vec.reserve(array1.len());
21+
vec.extend(array2);
22+
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// do not lint
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vec.reserve(1);
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vec.extend([1]);
26+
27+
//// do lint
28+
vec.reserve(array1.len());
29+
vec.extend(array1);
30+
31+
// do lint
32+
{
33+
vec.reserve(array1.len());
34+
vec.extend(array1)
35+
};
36+
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// do not lint
38+
vec.reserve(array1.len());
39+
vec.push(1);
40+
vec.extend(array1);
41+
42+
// do not lint
43+
let mut other_vec: Vec<usize> = vec![];
44+
other_vec.reserve(1);
45+
vec.extend([1])
46+
}
47+
48+
fn vec_deque_reserve() {
49+
let mut vec_deque: VecDeque<usize> = [1].into();
50+
let array: &[usize] = &[1, 2];
51+
52+
// do not lint
53+
vec_deque.reserve(1);
54+
vec_deque.extend([1]);
55+
56+
// do lint
57+
vec_deque.reserve(array.len());
58+
vec_deque.extend(array);
59+
60+
// do not lint
61+
{
62+
vec_deque.reserve(1);
63+
vec_deque.extend([1])
64+
};
65+
66+
// do not lint
67+
vec_deque.reserve(array.len() + 1);
68+
vec_deque.push_back(1);
69+
vec_deque.extend(array);
70+
71+
// do not lint
72+
let mut other_vec_deque: VecDeque<usize> = [1].into();
73+
other_vec_deque.reserve(1);
74+
vec_deque.extend([1])
75+
}
76+
77+
fn hash_map_reserve() {
78+
let mut map: HashMap<usize, usize> = HashMap::new();
79+
let mut other_map: HashMap<usize, usize> = HashMap::new();
80+
// do not lint
81+
map.reserve(other_map.len());
82+
map.extend(other_map);
83+
}
84+
85+
fn msrv_1_62() {
86+
#![clippy::msrv = "1.61"]
87+
let mut vec: Vec<usize> = vec![];
88+
let array: &[usize] = &[1, 2];
89+
90+
// do not lint
91+
vec.reserve(1);
92+
vec.extend([1]);
93+
94+
let mut vec_deque: VecDeque<usize> = [1].into();
95+
let array: &[usize] = &[1, 2];
96+
97+
// do not lint
98+
vec_deque.reserve(1);
99+
vec_deque.extend([1]);
100+
}

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