clippy_lints/src/strlen_on_c_strings.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::in_macro;
   3 use clippy_utils::paths;
   4 use clippy_utils::source::snippet_with_macro_callsite;
   5 use clippy_utils::ty::{is_type_diagnostic_item, is_type_ref_to_diagnostic_item};
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir as hir;
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::symbol::{sym, Symbol};
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for usage of `libc::strlen` on a `CString` or `CStr` value,
  15     /// and suggest calling `as_bytes().len()` or `to_bytes().len()` respectively instead.
  16     ///
  17     /// **Why is this bad?** This avoids calling an unsafe `libc` function.
  18     /// Currently, it also avoids calculating the length.
  19     ///
  20     /// **Known problems:** None.
  21     ///
  22     /// **Example:**
  23     ///
  24     /// ```rust, ignore
  25     /// use std::ffi::CString;
  26     /// let cstring = CString::new("foo").expect("CString::new failed");
  27     /// let len = unsafe { libc::strlen(cstring.as_ptr()) };
  28     /// ```
  29     /// Use instead:
  30     /// ```rust, no_run
  31     /// use std::ffi::CString;
  32     /// let cstring = CString::new("foo").expect("CString::new failed");
  33     /// let len = cstring.as_bytes().len();
  34     /// ```
  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 LateLintPass<'tcx> for StrlenOnCStrings {
  43     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
  44         if in_macro(expr.span) {
  45             return;
  46         }
  47
  48         if_chain! {
  49             if let hir::ExprKind::Call(func, [recv]) = expr.kind;
  50             if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = func.kind;
  51
  52             if (&paths::LIBC_STRLEN).iter().map(|x| Symbol::intern(x)).eq(
  53                 path.segments.iter().map(|seg| seg.ident.name));
  54             if let hir::ExprKind::MethodCall(path, _, args, _) = recv.kind;
  55             if args.len() == 1;
  56             if !args.iter().any(|e| e.span.from_expansion());
  57             if path.ident.name == sym::as_ptr;
  58             then {
  59                 let cstring = &args[0];
  60                 let ty = cx.typeck_results().expr_ty(cstring);
  61                 let val_name = snippet_with_macro_callsite(cx, cstring.span, "..");
  62                 let sugg = if is_type_diagnostic_item(cx, ty, sym::cstring_type){
  63                     format!("{}.as_bytes().len()", val_name)
  64                 } else if is_type_ref_to_diagnostic_item(cx, ty, sym::CStr){
  65                     format!("{}.to_bytes().len()", val_name)
  66                 } else {
  67                     return;
  68                 };
  69
  70                 span_lint_and_sugg(
  71                     cx,
  72                     STRLEN_ON_C_STRINGS,
  73                     expr.span,
  74                     "using `libc::strlen` on a `CString` or `CStr` value",
  75                     "try this (you might also need to get rid of `unsafe` block in some cases):",
  76                     sugg,
  77                     Applicability::Unspecified // Sometimes unnecessary `unsafe` block
  78                 );
  79             }
  80         }
  81     }
  82 }