use clippy_config::Conf;

use clippy_utils::consts::{ConstEvalCtxt, Constant};

use clippy_utils::diagnostics::span_lint_and_then;

use clippy_utils::higher::VecArgs;

use clippy_utils::macros::matching_root_macro_call;

use clippy_utils::msrvs::{self, Msrv};

use clippy_utils::source::snippet;

use clippy_utils::{expr_or_init, fn_def_id, std_or_core};

use rustc_errors::Applicability;

use rustc_hir::{Expr, ExprKind};

use rustc_lint::{LateContext, LateLintPass};

use rustc_session::impl_lint_pass;

use rustc_span::{Span, sym};

pub struct RepeatVecWithCapacity {

msrv: Msrv,

}

impl RepeatVecWithCapacity {

}

declare_clippy_lint! {

/// ### What it does

/// Looks for patterns such as `vec![Vec::with_capacity(x); n]` or `iter::repeat(Vec::with_capacity(x))`.

///

/// ### Why is this bad?

/// These constructs work by cloning the element, but cloning a `Vec<_>` does not

/// respect the old vector's capacity and effectively discards it.

///

/// This makes `iter::repeat(Vec::with_capacity(x))` especially suspicious because the user most certainly

/// expected that the yielded `Vec<_>` will have the requested capacity, otherwise one can simply write

/// `iter::repeat(Vec::new())` instead and it will have the same effect.

///

/// Similarly for `vec![x; n]`, the element `x` is cloned to fill the vec.

/// Unlike `iter::repeat` however, the vec repeat macro does not have to clone the value `n` times

/// but just `n - 1` times, because it can reuse the passed value for the last slot.

/// That means that the last `Vec<_>` gets the requested capacity but all other ones do not.

///

/// ### Example

/// ```rust

/// # use std::iter;

///

/// let _: Vec<Vec<u8>> = vec![Vec::with_capacity(42); 123];

/// let _: Vec<Vec<u8>> = iter::repeat(Vec::with_capacity(42)).take(123).collect();

/// ```

/// Use instead:

/// ```rust

/// # use std::iter;

///

/// let _: Vec<Vec<u8>> = iter::repeat_with(|| Vec::with_capacity(42)).take(123).collect();

/// // ^^^ this closure executes 123 times

/// // and the vecs will have the expected capacity

/// ```

#[clippy::version = "1.76.0"]

pub REPEAT_VEC_WITH_CAPACITY,

suspicious,

"repeating a `Vec::with_capacity` expression which does not retain capacity"

}

impl_lint_pass!(RepeatVecWithCapacity => [REPEAT_VEC_WITH_CAPACITY]);

fn emit_lint(cx: &LateContext<'_>, span: Span, kind: &str, note: &'static str, sugg_msg: &'static str, sugg: String) {

}

/// Checks `vec![Vec::with_capacity(x); n]`

fn check_vec_macro(cx: &LateContext<'_>, expr: &Expr<'_>) {

}

/// Checks `iter::repeat(Vec::with_capacity(x))`

fn check_repeat_fn(cx: &LateContext<'_>, expr: &Expr<'_>, msrv: Msrv) {

}

impl LateLintPass<'_> for RepeatVecWithCapacity {

}