compiler/rustc_lint/src/panic_fmt.rs

   1 use crate::{LateContext, LateLintPass, LintContext};
   2 use rustc_ast as ast;
   3 use rustc_errors::{pluralize, Applicability};
   4 use rustc_hir as hir;
   5 use rustc_middle::ty;
   6 use rustc_parse_format::{ParseMode, Parser, Piece};
   7 use rustc_span::{sym, InnerSpan};
   8
   9 declare_lint! {
  10     /// The `panic_fmt` lint detects `panic!("..")` with `{` or `}` in the string literal.
  11     ///
  12     /// ### Example
  13     ///
  14     /// ```rust,no_run
  15     /// panic!("{}");
  16     /// ```
  17     ///
  18     /// {{produces}}
  19     ///
  20     /// ### Explanation
  21     ///
  22     /// `panic!("{}")` panics with the message `"{}"`, as a `panic!()` invocation
  23     /// with a single argument does not use `format_args!()`.
  24     /// A future edition of Rust will interpret this string as format string,
  25     /// which would break this.
  26     PANIC_FMT,
  27     Warn,
  28     "detect braces in single-argument panic!() invocations",
  29     report_in_external_macro
  30 }
  31
  32 declare_lint_pass!(PanicFmt => [PANIC_FMT]);
  33
  34 impl<'tcx> LateLintPass<'tcx> for PanicFmt {
  35     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
  36         if let hir::ExprKind::Call(f, [arg]) = &expr.kind {
  37             if let &ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(f).kind() {
  38                 if Some(def_id) == cx.tcx.lang_items().begin_panic_fn()
  39                     || Some(def_id) == cx.tcx.lang_items().panic_fn()
  40                 {
  41                     check_panic(cx, f, arg);
  42                 }
  43             }
  44         }
  45     }
  46 }
  47
  48 fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tcx hir::Expr<'tcx>) {
  49     if let hir::ExprKind::Lit(lit) = &arg.kind {
  50         if let ast::LitKind::Str(sym, _) = lit.node {
  51             let mut expn = f.span.ctxt().outer_expn_data();
  52             if let Some(id) = expn.macro_def_id {
  53                 if cx.tcx.is_diagnostic_item(sym::std_panic_macro, id)
  54                     || cx.tcx.is_diagnostic_item(sym::core_panic_macro, id)
  55                 {
  56                     let fmt = sym.as_str();
  57                     if !fmt.contains(&['{', '}'][..]) {
  58                         return;
  59                     }
  60
  61                     let fmt_span = arg.span.source_callsite();
  62
  63                     let (snippet, style) =
  64                         match cx.sess().parse_sess.source_map().span_to_snippet(fmt_span) {
  65                             Ok(snippet) => {
  66                                 // Count the number of `#`s between the `r` and `"`.
  67                                 let style = snippet.strip_prefix('r').and_then(|s| s.find('"'));
  68                                 (Some(snippet), style)
  69                             }
  70                             Err(_) => (None, None),
  71                         };
  72
  73                     let mut fmt_parser =
  74                         Parser::new(fmt.as_ref(), style, snippet.clone(), false, ParseMode::Format);
  75                     let n_arguments =
  76                         (&mut fmt_parser).filter(|a| matches!(a, Piece::NextArgument(_))).count();
  77
  78                     // Unwrap another level of macro expansion if this panic!()
  79                     // was expanded from assert!() or debug_assert!().
  80                     for &assert in &[sym::assert_macro, sym::debug_assert_macro] {
  81                         let parent = expn.call_site.ctxt().outer_expn_data();
  82                         if parent
  83                             .macro_def_id
  84                             .map_or(false, |id| cx.tcx.is_diagnostic_item(assert, id))
  85                         {
  86                             expn = parent;
  87                         }
  88                     }
  89
  90                     if n_arguments > 0 && fmt_parser.errors.is_empty() {
  91                         let arg_spans: Vec<_> = match &fmt_parser.arg_places[..] {
  92                             [] => vec![fmt_span],
  93                             v => v.iter().map(|span| fmt_span.from_inner(*span)).collect(),
  94                         };
  95                         cx.struct_span_lint(PANIC_FMT, arg_spans, |lint| {
  96                             let mut l = lint.build(match n_arguments {
  97                                 1 => "panic message contains an unused formatting placeholder",
  98                                 _ => "panic message contains unused formatting placeholders",
  99                             });
 100                             l.note("this message is not used as a format string when given without arguments, but will be in a future Rust edition");
 101                             if expn.call_site.contains(arg.span) {
 102                                 l.span_suggestion(
 103                                     arg.span.shrink_to_hi(),
 104                                     &format!("add the missing argument{}", pluralize!(n_arguments)),
 105                                     ", ...".into(),
 106                                     Applicability::HasPlaceholders,
 107                                 );
 108                                 l.span_suggestion(
 109                                     arg.span.shrink_to_lo(),
 110                                     "or add a \"{}\" format string to use the message literally",
 111                                     "\"{}\", ".into(),
 112                                     Applicability::MachineApplicable,
 113                                 );
 114                             }
 115                             l.emit();
 116                         });
 117                     } else {
 118                         let brace_spans: Option<Vec<_>> = snippet
 119                             .filter(|s| s.starts_with('"') || s.starts_with("r#"))
 120                             .map(|s| {
 121                                 s.char_indices()
 122                                     .filter(|&(_, c)| c == '{' || c == '}')
 123                                     .map(|(i, _)| {
 124                                         fmt_span.from_inner(InnerSpan { start: i, end: i + 1 })
 125                                     })
 126                                     .collect()
 127                             });
 128                         let msg = match &brace_spans {
 129                             Some(v) if v.len() == 1 => "panic message contains a brace",
 130                             _ => "panic message contains braces",
 131                         };
 132                         cx.struct_span_lint(PANIC_FMT, brace_spans.unwrap_or(vec![expn.call_site]), |lint| {
 133                             let mut l = lint.build(msg);
 134                             l.note("this message is not used as a format string, but will be in a future Rust edition");
 135                             if expn.call_site.contains(arg.span) {
 136                                 l.span_suggestion(
 137                                     arg.span.shrink_to_lo(),
 138                                     "add a \"{}\" format string to use the message literally",
 139                                     "\"{}\", ".into(),
 140                                     Applicability::MachineApplicable,
 141                                 );
 142                             }
 143                             l.emit();
 144                         });
 145                     }
 146                 }
 147             }
 148         }
 149     }
 150 }