src/tools/clippy/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
  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     pub STRLEN_ON_C_STRINGS,
  35     complexity,
  36     "using `libc::strlen` on a `CString` or `CStr` value, while `as_bytes().len()` or `to_bytes().len()` respectively can be used instead"
  37 }
  38
  39 declare_lint_pass!(StrlenOnCStrings => [STRLEN_ON_C_STRINGS]);
  40
  41 impl LateLintPass<'tcx> for StrlenOnCStrings {
  42     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
  43         if in_macro(expr.span) {
  44             return;
  45         }
  46
  47         if_chain! {
  48             if let hir::ExprKind::Call(func, [recv]) = expr.kind;
  49             if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = func.kind;
  50
  51             if (&paths::LIBC_STRLEN).iter().map(|x| Symbol::intern(x)).eq(
  52                 path.segments.iter().map(|seg| seg.ident.name));
  53             if let hir::ExprKind::MethodCall(path, _, args, _) = recv.kind;
  54             if args.len() == 1;
  55             if !args.iter().any(|e| e.span.from_expansion());
  56             if path.ident.name == sym::as_ptr;
  57             then {
  58                 let cstring = &args[0];
  59                 let ty = cx.typeck_results().expr_ty(cstring);
  60                 let val_name = snippet_with_macro_callsite(cx, cstring.span, "..");
  61                 let sugg = if is_type_diagnostic_item(cx, ty, sym::cstring_type){
  62                     format!("{}.as_bytes().len()", val_name)
  63                 } else if is_type_ref_to_diagnostic_item(cx, ty, sym::CStr){
  64                     format!("{}.to_bytes().len()", val_name)
  65                 } else {
  66                     return;
  67                 };
  68
  69                 span_lint_and_sugg(
  70                     cx,
  71                     STRLEN_ON_C_STRINGS,
  72                     expr.span,
  73                     "using `libc::strlen` on a `CString` or `CStr` value",
  74                     "try this (you might also need to get rid of `unsafe` block in some cases):",
  75                     sugg,
  76                     Applicability::Unspecified // Sometimes unnecessary `unsafe` block
  77                 );
  78             }
  79         }
  80     }
  81 }