84 lines
2.9 KiB
Rust
84 lines
2.9 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_help;
|
|
use clippy_utils::ty::is_type_lang_item;
|
|
use clippy_utils::{match_def_path, paths, peel_hir_expr_refs};
|
|
use rustc_hir::{BinOpKind, Expr, ExprKind, LangItem};
|
|
use rustc_lint::{LateContext, LateLintPass};
|
|
use rustc_session::{declare_lint_pass, declare_tool_lint};
|
|
use rustc_span::sym;
|
|
|
|
declare_clippy_lint! {
|
|
/// ### What it does
|
|
/// Detects cases where the result of a `format!` call is
|
|
/// appended to an existing `String`.
|
|
///
|
|
/// ### Why is this bad?
|
|
/// Introduces an extra, avoidable heap allocation.
|
|
///
|
|
/// ### Known problems
|
|
/// `format!` returns a `String` but `write!` returns a `Result`.
|
|
/// Thus you are forced to ignore the `Err` variant to achieve the same API.
|
|
///
|
|
/// While using `write!` in the suggested way should never fail, this isn't necessarily clear to the programmer.
|
|
///
|
|
/// ### Example
|
|
/// ```rust
|
|
/// let mut s = String::new();
|
|
/// s += &format!("0x{:X}", 1024);
|
|
/// s.push_str(&format!("0x{:X}", 1024));
|
|
/// ```
|
|
/// Use instead:
|
|
/// ```rust
|
|
/// use std::fmt::Write as _; // import without risk of name clashing
|
|
///
|
|
/// let mut s = String::new();
|
|
/// let _ = write!(s, "0x{:X}", 1024);
|
|
/// ```
|
|
#[clippy::version = "1.62.0"]
|
|
pub FORMAT_PUSH_STRING,
|
|
restriction,
|
|
"`format!(..)` appended to existing `String`"
|
|
}
|
|
declare_lint_pass!(FormatPushString => [FORMAT_PUSH_STRING]);
|
|
|
|
fn is_string(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
|
|
is_type_lang_item(cx, cx.typeck_results().expr_ty(e).peel_refs(), LangItem::String)
|
|
}
|
|
fn is_format(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
|
|
if let Some(macro_def_id) = e.span.ctxt().outer_expn_data().macro_def_id {
|
|
cx.tcx.get_diagnostic_name(macro_def_id) == Some(sym::format_macro)
|
|
} else {
|
|
false
|
|
}
|
|
}
|
|
|
|
impl<'tcx> LateLintPass<'tcx> for FormatPushString {
|
|
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
|
|
let arg = match expr.kind {
|
|
ExprKind::MethodCall(_, _, [arg], _) => {
|
|
if let Some(fn_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) &&
|
|
match_def_path(cx, fn_def_id, &paths::PUSH_STR) {
|
|
arg
|
|
} else {
|
|
return;
|
|
}
|
|
}
|
|
ExprKind::AssignOp(op, left, arg)
|
|
if op.node == BinOpKind::Add && is_string(cx, left) => {
|
|
arg
|
|
},
|
|
_ => return,
|
|
};
|
|
let (arg, _) = peel_hir_expr_refs(arg);
|
|
if is_format(cx, arg) {
|
|
span_lint_and_help(
|
|
cx,
|
|
FORMAT_PUSH_STRING,
|
|
expr.span,
|
|
"`format!(..)` appended to existing `String`",
|
|
None,
|
|
"consider using `write!` to avoid the extra allocation",
|
|
);
|
|
}
|
|
}
|
|
}
|