rust-clippy/clippy_lints/src/vec_init_then_push.rs

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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::{match_def_path, path_to_local, path_to_local_id, paths};
use if_chain::if_chain;
use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, Local, PatKind, QPath, Stmt, StmtKind};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{symbol::sym, Span};
use std::convert::TryInto;
declare_clippy_lint! {
/// **What it does:** Checks for calls to `push` immediately after creating a new `Vec`.
///
/// **Why is this bad?** The `vec![]` macro is both more performant and easier to read than
/// multiple `push` calls.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let mut v = Vec::new();
/// v.push(0);
/// ```
/// Use instead:
/// ```rust
/// let v = vec![0];
/// ```
pub VEC_INIT_THEN_PUSH,
perf,
"`push` immediately after `Vec` creation"
}
impl_lint_pass!(VecInitThenPush => [VEC_INIT_THEN_PUSH]);
#[derive(Default)]
pub struct VecInitThenPush {
searcher: Option<VecPushSearcher>,
}
#[derive(Clone, Copy)]
enum VecInitKind {
New,
WithCapacity(u64),
}
struct VecPushSearcher {
local_id: HirId,
init: VecInitKind,
lhs_is_local: bool,
lhs_span: Span,
err_span: Span,
found: u64,
}
impl VecPushSearcher {
fn display_err(&self, cx: &LateContext<'_>) {
match self.init {
_ if self.found == 0 => return,
VecInitKind::WithCapacity(x) if x > self.found => return,
_ => (),
};
let mut s = if self.lhs_is_local {
String::from("let ")
} else {
String::new()
};
s.push_str(&snippet(cx, self.lhs_span, ".."));
s.push_str(" = vec![..];");
span_lint_and_sugg(
cx,
VEC_INIT_THEN_PUSH,
self.err_span,
"calls to `push` immediately after creation",
"consider using the `vec![]` macro",
s,
Applicability::HasPlaceholders,
);
}
}
impl LateLintPass<'_> for VecInitThenPush {
fn check_block(&mut self, _: &LateContext<'tcx>, _: &'tcx Block<'tcx>) {
self.searcher = None;
}
fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'tcx>) {
if_chain! {
if !in_external_macro(cx.sess(), local.span);
if let Some(init) = local.init;
if let PatKind::Binding(BindingAnnotation::Mutable, id, _, None) = local.pat.kind;
if let Some(init_kind) = get_vec_init_kind(cx, init);
then {
self.searcher = Some(VecPushSearcher {
local_id: id,
init: init_kind,
lhs_is_local: true,
lhs_span: local.ty.map_or(local.pat.span, |t| local.pat.span.to(t.span)),
err_span: local.span,
found: 0,
});
}
}
}
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if_chain! {
if self.searcher.is_none();
if !in_external_macro(cx.sess(), expr.span);
if let ExprKind::Assign(left, right, _) = expr.kind;
if let Some(id) = path_to_local(left);
if let Some(init_kind) = get_vec_init_kind(cx, right);
then {
self.searcher = Some(VecPushSearcher {
local_id: id,
init: init_kind,
lhs_is_local: false,
lhs_span: left.span,
err_span: expr.span,
found: 0,
});
}
}
}
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
if let Some(searcher) = self.searcher.take() {
if_chain! {
if let StmtKind::Expr(expr) | StmtKind::Semi(expr) = stmt.kind;
if let ExprKind::MethodCall(path, _, [self_arg, _], _) = expr.kind;
if path_to_local_id(self_arg, searcher.local_id);
if path.ident.name.as_str() == "push";
then {
self.searcher = Some(VecPushSearcher {
found: searcher.found + 1,
err_span: searcher.err_span.to(stmt.span),
.. searcher
});
} else {
searcher.display_err(cx);
}
}
}
}
fn check_block_post(&mut self, cx: &LateContext<'tcx>, _: &'tcx Block<'tcx>) {
if let Some(searcher) = self.searcher.take() {
searcher.display_err(cx);
}
}
}
fn get_vec_init_kind<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Option<VecInitKind> {
if let ExprKind::Call(func, args) = expr.kind {
match func.kind {
ExprKind::Path(QPath::TypeRelative(ty, name))
if is_type_diagnostic_item(cx, cx.typeck_results().node_type(ty.hir_id), sym::vec_type) =>
{
if name.ident.name == sym::new {
return Some(VecInitKind::New);
} else if name.ident.name.as_str() == "with_capacity" {
return args.get(0).and_then(|arg| {
if_chain! {
if let ExprKind::Lit(lit) = &arg.kind;
if let LitKind::Int(num, _) = lit.node;
then {
Some(VecInitKind::WithCapacity(num.try_into().ok()?))
} else {
None
}
}
});
}
}
ExprKind::Path(QPath::Resolved(_, path))
if match_def_path(cx, path.res.opt_def_id()?, &paths::DEFAULT_TRAIT_METHOD)
&& is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::vec_type) =>
{
return Some(VecInitKind::New);
}
_ => (),
}
}
None
}