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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_context;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::visitors::is_expr_unsafe;
use clippy_utils::{get_parent_node, match_libc_symbol};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Block, BlockCheckMode, Expr, ExprKind, Node, UnsafeSource};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::symbol::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for usage of `libc::strlen` on a `CString` or `CStr` value,
/// and suggest calling `as_bytes().len()` or `to_bytes().len()` respectively instead.
///
/// ### Why is this bad?
/// This avoids calling an unsafe `libc` function.
/// Currently, it also avoids calculating the length.
///
/// ### Example
/// ```rust, ignore
/// use std::ffi::CString;
/// let cstring = CString::new("foo").expect("CString::new failed");
/// let len = unsafe { libc::strlen(cstring.as_ptr()) };
/// ```
/// Use instead:
/// ```rust, no_run
/// use std::ffi::CString;
/// let cstring = CString::new("foo").expect("CString::new failed");
/// let len = cstring.as_bytes().len();
/// ```
#[clippy::version = "1.55.0"]
pub STRLEN_ON_C_STRINGS,
complexity,
"using `libc::strlen` on a `CString` or `CStr` value, while `as_bytes().len()` or `to_bytes().len()` respectively can be used instead"
}
declare_lint_pass!(StrlenOnCStrings => [STRLEN_ON_C_STRINGS]);
impl<'tcx> LateLintPass<'tcx> for StrlenOnCStrings {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if_chain! {
if !expr.span.from_expansion();
if let ExprKind::Call(func, [recv]) = expr.kind;
if let ExprKind::Path(path) = &func.kind;
if let Some(did) = cx.qpath_res(path, func.hir_id).opt_def_id();
if match_libc_symbol(cx, did, "strlen");
if let ExprKind::MethodCall(path, [self_arg], _) = recv.kind;
if !recv.span.from_expansion();
if path.ident.name == sym::as_ptr;
then {
let ctxt = expr.span.ctxt();
let span = match get_parent_node(cx.tcx, expr.hir_id) {
Some(Node::Block(&Block {
rules: BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided), span, ..
}))
if span.ctxt() == ctxt && !is_expr_unsafe(cx, self_arg) => {
span
}
_ => expr.span,
};
let ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
let mut app = Applicability::MachineApplicable;
let val_name = snippet_with_context(cx, self_arg.span, ctxt, "..", &mut app).0;
let method_name = if is_type_diagnostic_item(cx, ty, sym::cstring_type) {
"as_bytes"
} else if is_type_diagnostic_item(cx, ty, sym::CStr) {
"to_bytes"
} else {
return;
};
span_lint_and_sugg(
cx,
STRLEN_ON_C_STRINGS,
span,
"using `libc::strlen` on a `CString` or `CStr` value",
"try this",
format!("{}.{}().len()", val_name, method_name),
app,
);
}
}
}
}
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