clippy_lints/src/strlen_on_c_strings.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet_with_context;
   3 use clippy_utils::ty::is_type_diagnostic_item;
   4 use clippy_utils::visitors::is_expr_unsafe;
   5 use clippy_utils::{get_parent_node, match_libc_symbol};
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{Block, BlockCheckMode, Expr, ExprKind, Node, UnsafeSource};
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::symbol::sym;
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for usage of `libc::strlen` on a `CString` or `CStr` value,
  16     /// and suggest calling `as_bytes().len()` or `to_bytes().len()` respectively instead.
  17     ///
  18     /// ### Why is this bad?
  19     /// This avoids calling an unsafe `libc` function.
  20     /// Currently, it also avoids calculating the length.
  21     ///
  22     /// ### Example
  23     /// ```rust, ignore
  24     /// use std::ffi::CString;
  25     /// let cstring = CString::new("foo").expect("CString::new failed");
  26     /// let len = unsafe { libc::strlen(cstring.as_ptr()) };
  27     /// ```
  28     /// Use instead:
  29     /// ```rust, no_run
  30     /// use std::ffi::CString;
  31     /// let cstring = CString::new("foo").expect("CString::new failed");
  32     /// let len = cstring.as_bytes().len();
  33     /// ```
  34     #[clippy::version = "1.55.0"]
  35     pub STRLEN_ON_C_STRINGS,
  36     complexity,
  37     "using `libc::strlen` on a `CString` or `CStr` value, while `as_bytes().len()` or `to_bytes().len()` respectively can be used instead"
  38 }
  39
  40 declare_lint_pass!(StrlenOnCStrings => [STRLEN_ON_C_STRINGS]);
  41
  42 impl<'tcx> LateLintPass<'tcx> for StrlenOnCStrings {
  43     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  44         if_chain! {
  45             if !expr.span.from_expansion();
  46             if let ExprKind::Call(func, [recv]) = expr.kind;
  47             if let ExprKind::Path(path) = &func.kind;
  48             if let Some(did) = cx.qpath_res(path, func.hir_id).opt_def_id();
  49             if match_libc_symbol(cx, did, "strlen");
  50             if let ExprKind::MethodCall(path, self_arg, [], _) = recv.kind;
  51             if !recv.span.from_expansion();
  52             if path.ident.name == sym::as_ptr;
  53             then {
  54                 let ctxt = expr.span.ctxt();
  55                 let span = match get_parent_node(cx.tcx, expr.hir_id) {
  56                     Some(Node::Block(&Block {
  57                         rules: BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided), span, ..
  58                     }))
  59                     if span.ctxt() == ctxt && !is_expr_unsafe(cx, self_arg) => {
  60                         span
  61                     }
  62                     _ => expr.span,
  63                 };
  64
  65                 let ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
  66                 let mut app = Applicability::MachineApplicable;
  67                 let val_name = snippet_with_context(cx, self_arg.span, ctxt, "..", &mut app).0;
  68                 let method_name = if is_type_diagnostic_item(cx, ty, sym::cstring_type) {
  69                     "as_bytes"
  70                 } else if is_type_diagnostic_item(cx, ty, sym::CStr) {
  71                     "to_bytes"
  72                 } else {
  73                     return;
  74                 };
  75
  76                 span_lint_and_sugg(
  77                     cx,
  78                     STRLEN_ON_C_STRINGS,
  79                     span,
  80                     "using `libc::strlen` on a `CString` or `CStr` value",
  81                     "try this",
  82                     format!("{}.{}().len()", val_name, method_name),
  83                     app,
  84                 );
  85             }
  86         }
  87     }
  88 }