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|
use clippy_utils::{
diagnostics::{span_lint, span_lint_and_sugg},
higher::{get_vec_init_kind, VecInitKind},
source::snippet,
visitors::expr_visitor_no_bodies,
};
use hir::{intravisit::Visitor, ExprKind, Local, PatKind, PathSegment, QPath, StmtKind};
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// This lint catches reads into a zero-length `Vec`.
/// Especially in the case of a call to `with_capacity`, this lint warns that read
/// gets the number of bytes from the `Vec`'s length, not its capacity.
///
/// ### Why is this bad?
/// Reading zero bytes is almost certainly not the intended behavior.
///
/// ### Known problems
/// In theory, a very unusual read implementation could assign some semantic meaning
/// to zero-byte reads. But it seems exceptionally unlikely that code intending to do
/// a zero-byte read would allocate a `Vec` for it.
///
/// ### Example
/// ```rust
/// use std::io;
/// fn foo<F: io::Read>(mut f: F) {
/// let mut data = Vec::with_capacity(100);
/// f.read(&mut data).unwrap();
/// }
/// ```
/// Use instead:
/// ```rust
/// use std::io;
/// fn foo<F: io::Read>(mut f: F) {
/// let mut data = Vec::with_capacity(100);
/// data.resize(100, 0);
/// f.read(&mut data).unwrap();
/// }
/// ```
#[clippy::version = "1.63.0"]
pub READ_ZERO_BYTE_VEC,
nursery,
"checks for reads into a zero-length `Vec`"
}
declare_lint_pass!(ReadZeroByteVec => [READ_ZERO_BYTE_VEC]);
impl<'tcx> LateLintPass<'tcx> for ReadZeroByteVec {
fn check_block(&mut self, cx: &LateContext<'tcx>, block: &hir::Block<'tcx>) {
for (idx, stmt) in block.stmts.iter().enumerate() {
if !stmt.span.from_expansion()
// matches `let v = Vec::new();`
&& let StmtKind::Local(local) = stmt.kind
&& let Local { pat, init: Some(init), .. } = local
&& let PatKind::Binding(_, _, ident, _) = pat.kind
&& let Some(vec_init_kind) = get_vec_init_kind(cx, init)
{
// finds use of `_.read(&mut v)`
let mut read_found = false;
let mut visitor = expr_visitor_no_bodies(|expr| {
if let ExprKind::MethodCall(path, _self, [arg], _) = expr.kind
&& let PathSegment { ident: read_or_read_exact, .. } = *path
&& matches!(read_or_read_exact.as_str(), "read" | "read_exact")
&& let ExprKind::AddrOf(_, hir::Mutability::Mut, inner) = arg.kind
&& let ExprKind::Path(QPath::Resolved(None, inner_path)) = inner.kind
&& let [inner_seg] = inner_path.segments
&& ident.name == inner_seg.ident.name
{
read_found = true;
}
!read_found
});
let next_stmt_span;
if idx == block.stmts.len() - 1 {
// case { .. stmt; expr }
if let Some(e) = block.expr {
visitor.visit_expr(e);
next_stmt_span = e.span;
} else {
return;
}
} else {
// case { .. stmt; stmt; .. }
let next_stmt = &block.stmts[idx + 1];
visitor.visit_stmt(next_stmt);
next_stmt_span = next_stmt.span;
}
drop(visitor);
if read_found && !next_stmt_span.from_expansion() {
let applicability = Applicability::MaybeIncorrect;
match vec_init_kind {
VecInitKind::WithConstCapacity(len) => {
span_lint_and_sugg(
cx,
READ_ZERO_BYTE_VEC,
next_stmt_span,
"reading zero byte data to `Vec`",
"try",
format!("{}.resize({}, 0); {}",
ident.as_str(),
len,
snippet(cx, next_stmt_span, "..")
),
applicability,
);
}
VecInitKind::WithExprCapacity(hir_id) => {
let e = cx.tcx.hir().expect_expr(hir_id);
span_lint_and_sugg(
cx,
READ_ZERO_BYTE_VEC,
next_stmt_span,
"reading zero byte data to `Vec`",
"try",
format!("{}.resize({}, 0); {}",
ident.as_str(),
snippet(cx, e.span, ".."),
snippet(cx, next_stmt_span, "..")
),
applicability,
);
}
_ => {
span_lint(
cx,
READ_ZERO_BYTE_VEC,
next_stmt_span,
"reading zero byte data to `Vec`",
);
}
}
}
}
}
}
}
|
