compiler/rustc_lint/src/non_fmt_panic.rs

   1 use crate::{LateContext, LateLintPass, LintContext};
   2 use rustc_ast as ast;
   3 use rustc_errors::{fluent, Applicability};
   4 use rustc_hir as hir;
   5 use rustc_infer::infer::TyCtxtInferExt;
   6 use rustc_middle::lint::in_external_macro;
   7 use rustc_middle::ty;
   8 use rustc_middle::ty::subst::InternalSubsts;
   9 use rustc_parse_format::{ParseMode, Parser, Piece};
  10 use rustc_session::lint::FutureIncompatibilityReason;
  11 use rustc_span::edition::Edition;
  12 use rustc_span::{hygiene, sym, symbol::kw, InnerSpan, Span, Symbol};
  13 use rustc_trait_selection::infer::InferCtxtExt;
  14
  15 declare_lint! {
  16     /// The `non_fmt_panics` lint detects `panic!(..)` invocations where the first
  17     /// argument is not a formatting string.
  18     ///
  19     /// ### Example
  20     ///
  21     /// ```rust,no_run,edition2018
  22     /// panic!("{}");
  23     /// panic!(123);
  24     /// ```
  25     ///
  26     /// {{produces}}
  27     ///
  28     /// ### Explanation
  29     ///
  30     /// In Rust 2018 and earlier, `panic!(x)` directly uses `x` as the message.
  31     /// That means that `panic!("{}")` panics with the message `"{}"` instead
  32     /// of using it as a formatting string, and `panic!(123)` will panic with
  33     /// an `i32` as message.
  34     ///
  35     /// Rust 2021 always interprets the first argument as format string.
  36     NON_FMT_PANICS,
  37     Warn,
  38     "detect single-argument panic!() invocations in which the argument is not a format string",
  39     @future_incompatible = FutureIncompatibleInfo {
  40         reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
  41         explain_reason: false,
  42     };
  43     report_in_external_macro
  44 }
  45
  46 declare_lint_pass!(NonPanicFmt => [NON_FMT_PANICS]);
  47
  48 impl<'tcx> LateLintPass<'tcx> for NonPanicFmt {
  49     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
  50         if let hir::ExprKind::Call(f, [arg]) = &expr.kind {
  51             if let &ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(f).kind() {
  52                 let f_diagnostic_name = cx.tcx.get_diagnostic_name(def_id);
  53
  54                 if Some(def_id) == cx.tcx.lang_items().begin_panic_fn()
  55                     || Some(def_id) == cx.tcx.lang_items().panic_fn()
  56                     || f_diagnostic_name == Some(sym::panic_str)
  57                 {
  58                     if let Some(id) = f.span.ctxt().outer_expn_data().macro_def_id {
  59                         if matches!(
  60                             cx.tcx.get_diagnostic_name(id),
  61                             Some(sym::core_panic_2015_macro | sym::std_panic_2015_macro)
  62                         ) {
  63                             check_panic(cx, f, arg);
  64                         }
  65                     }
  66                 } else if f_diagnostic_name == Some(sym::unreachable_display) {
  67                     if let Some(id) = f.span.ctxt().outer_expn_data().macro_def_id {
  68                         if cx.tcx.is_diagnostic_item(sym::unreachable_2015_macro, id) {
  69                             check_panic(
  70                                 cx,
  71                                 f,
  72                                 // This is safe because we checked above that the callee is indeed
  73                                 // unreachable_display
  74                                 match &arg.kind {
  75                                     // Get the borrowed arg not the borrow
  76                                     hir::ExprKind::AddrOf(ast::BorrowKind::Ref, _, arg) => arg,
  77                                     _ => bug!("call to unreachable_display without borrow"),
  78                                 },
  79                             );
  80                         }
  81                     }
  82                 }
  83             }
  84         }
  85     }
  86 }
  87
  88 fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tcx hir::Expr<'tcx>) {
  89     if let hir::ExprKind::Lit(lit) = &arg.kind {
  90         if let ast::LitKind::Str(sym, _) = lit.node {
  91             // The argument is a string literal.
  92             check_panic_str(cx, f, arg, sym.as_str());
  93             return;
  94         }
  95     }
  96
  97     // The argument is *not* a string literal.
  98
  99     let (span, panic, symbol) = panic_call(cx, f);
 100
 101     if in_external_macro(cx.sess(), span) {
 102         // Nothing that can be done about it in the current crate.
 103         return;
 104     }
 105
 106     // Find the span of the argument to `panic!()` or `unreachable!`, before expansion in the
 107     // case of `panic!(some_macro!())` or `unreachable!(some_macro!())`.
 108     // We don't use source_callsite(), because this `panic!(..)` might itself
 109     // be expanded from another macro, in which case we want to stop at that
 110     // expansion.
 111     let mut arg_span = arg.span;
 112     let mut arg_macro = None;
 113     while !span.contains(arg_span) {
 114         let expn = arg_span.ctxt().outer_expn_data();
 115         if expn.is_root() {
 116             break;
 117         }
 118         arg_macro = expn.macro_def_id;
 119         arg_span = expn.call_site;
 120     }
 121
 122     cx.struct_span_lint(NON_FMT_PANICS, arg_span, |lint| {
 123         let mut l = lint.build(fluent::lint::non_fmt_panic);
 124         l.set_arg("name", symbol);
 125         l.note(fluent::lint::note);
 126         l.note(fluent::lint::more_info_note);
 127         if !is_arg_inside_call(arg_span, span) {
 128             // No clue where this argument is coming from.
 129             l.emit();
 130             return;
 131         }
 132         if arg_macro.map_or(false, |id| cx.tcx.is_diagnostic_item(sym::format_macro, id)) {
 133             // A case of `panic!(format!(..))`.
 134             l.note(fluent::lint::supports_fmt_note);
 135             if let Some((open, close, _)) = find_delimiters(cx, arg_span) {
 136                 l.multipart_suggestion(
 137                     fluent::lint::supports_fmt_suggestion,
 138                     vec![
 139                         (arg_span.until(open.shrink_to_hi()), "".into()),
 140                         (close.until(arg_span.shrink_to_hi()), "".into()),
 141                     ],
 142                     Applicability::MachineApplicable,
 143                 );
 144             }
 145         } else {
 146             let ty = cx.typeck_results().expr_ty(arg);
 147             // If this is a &str or String, we can confidently give the `"{}", ` suggestion.
 148             let is_str = matches!(
 149                 ty.kind(),
 150                 ty::Ref(_, r, _) if *r.kind() == ty::Str,
 151             ) || matches!(
 152                 ty.ty_adt_def(),
 153                 Some(ty_def) if cx.tcx.is_diagnostic_item(sym::String, ty_def.did()),
 154             );
 155
 156             let (suggest_display, suggest_debug) = cx.tcx.infer_ctxt().enter(|infcx| {
 157                 let display = is_str
 158                     || cx.tcx.get_diagnostic_item(sym::Display).map(|t| {
 159                         infcx
 160                             .type_implements_trait(t, ty, InternalSubsts::empty(), cx.param_env)
 161                             .may_apply()
 162                     }) == Some(true);
 163                 let debug = !display
 164                     && cx.tcx.get_diagnostic_item(sym::Debug).map(|t| {
 165                         infcx
 166                             .type_implements_trait(t, ty, InternalSubsts::empty(), cx.param_env)
 167                             .may_apply()
 168                     }) == Some(true);
 169                 (display, debug)
 170             });
 171
 172             let suggest_panic_any = !is_str && panic == sym::std_panic_macro;
 173
 174             let fmt_applicability = if suggest_panic_any {
 175                 // If we can use panic_any, use that as the MachineApplicable suggestion.
 176                 Applicability::MaybeIncorrect
 177             } else {
 178                 // If we don't suggest panic_any, using a format string is our best bet.
 179                 Applicability::MachineApplicable
 180             };
 181
 182             if suggest_display {
 183                 l.span_suggestion_verbose(
 184                     arg_span.shrink_to_lo(),
 185                     fluent::lint::display_suggestion,
 186                     "\"{}\", ",
 187                     fmt_applicability,
 188                 );
 189             } else if suggest_debug {
 190                 l.set_arg("ty", ty);
 191                 l.span_suggestion_verbose(
 192                     arg_span.shrink_to_lo(),
 193                     fluent::lint::debug_suggestion,
 194                     "\"{:?}\", ",
 195                     fmt_applicability,
 196                 );
 197             }
 198
 199             if suggest_panic_any {
 200                 if let Some((open, close, del)) = find_delimiters(cx, span) {
 201                     l.set_arg("already_suggested", suggest_display || suggest_debug);
 202                     l.multipart_suggestion(
 203                         fluent::lint::panic_suggestion,
 204                         if del == '(' {
 205                             vec![(span.until(open), "std::panic::panic_any".into())]
 206                         } else {
 207                             vec![
 208                                 (span.until(open.shrink_to_hi()), "std::panic::panic_any(".into()),
 209                                 (close, ")".into()),
 210                             ]
 211                         },
 212                         Applicability::MachineApplicable,
 213                     );
 214                 }
 215             }
 216         }
 217         l.emit();
 218     });
 219 }
 220
 221 fn check_panic_str<'tcx>(
 222     cx: &LateContext<'tcx>,
 223     f: &'tcx hir::Expr<'tcx>,
 224     arg: &'tcx hir::Expr<'tcx>,
 225     fmt: &str,
 226 ) {
 227     if !fmt.contains(&['{', '}']) {
 228         // No brace, no problem.
 229         return;
 230     }
 231
 232     let (span, _, _) = panic_call(cx, f);
 233
 234     if in_external_macro(cx.sess(), span) && in_external_macro(cx.sess(), arg.span) {
 235         // Nothing that can be done about it in the current crate.
 236         return;
 237     }
 238
 239     let fmt_span = arg.span.source_callsite();
 240
 241     let (snippet, style) = match cx.sess().parse_sess.source_map().span_to_snippet(fmt_span) {
 242         Ok(snippet) => {
 243             // Count the number of `#`s between the `r` and `"`.
 244             let style = snippet.strip_prefix('r').and_then(|s| s.find('"'));
 245             (Some(snippet), style)
 246         }
 247         Err(_) => (None, None),
 248     };
 249
 250     let mut fmt_parser = Parser::new(fmt, style, snippet.clone(), false, ParseMode::Format);
 251     let n_arguments = (&mut fmt_parser).filter(|a| matches!(a, Piece::NextArgument(_))).count();
 252
 253     if n_arguments > 0 && fmt_parser.errors.is_empty() {
 254         let arg_spans: Vec<_> = match &fmt_parser.arg_places[..] {
 255             [] => vec![fmt_span],
 256             v => v
 257                 .iter()
 258                 .map(|span| fmt_span.from_inner(InnerSpan::new(span.start, span.end)))
 259                 .collect(),
 260         };
 261         cx.struct_span_lint(NON_FMT_PANICS, arg_spans, |lint| {
 262             let mut l = lint.build(fluent::lint::non_fmt_panic_unused);
 263             l.set_arg("count", n_arguments);
 264             l.note(fluent::lint::note);
 265             if is_arg_inside_call(arg.span, span) {
 266                 l.span_suggestion(
 267                     arg.span.shrink_to_hi(),
 268                     fluent::lint::add_args_suggestion,
 269                     ", ...",
 270                     Applicability::HasPlaceholders,
 271                 );
 272                 l.span_suggestion(
 273                     arg.span.shrink_to_lo(),
 274                     fluent::lint::add_fmt_suggestion,
 275                     "\"{}\", ",
 276                     Applicability::MachineApplicable,
 277                 );
 278             }
 279             l.emit();
 280         });
 281     } else {
 282         let brace_spans: Option<Vec<_>> =
 283             snippet.filter(|s| s.starts_with('"') || s.starts_with("r#")).map(|s| {
 284                 s.char_indices()
 285                     .filter(|&(_, c)| c == '{' || c == '}')
 286                     .map(|(i, _)| fmt_span.from_inner(InnerSpan { start: i, end: i + 1 }))
 287                     .collect()
 288             });
 289         let count = brace_spans.as_ref().map(|v| v.len()).unwrap_or(/* any number >1 */ 2);
 290         cx.struct_span_lint(NON_FMT_PANICS, brace_spans.unwrap_or_else(|| vec![span]), |lint| {
 291             let mut l = lint.build(fluent::lint::non_fmt_panic_braces);
 292             l.set_arg("count", count);
 293             l.note(fluent::lint::note);
 294             if is_arg_inside_call(arg.span, span) {
 295                 l.span_suggestion(
 296                     arg.span.shrink_to_lo(),
 297                     fluent::lint::suggestion,
 298                     "\"{}\", ",
 299                     Applicability::MachineApplicable,
 300                 );
 301             }
 302             l.emit();
 303         });
 304     }
 305 }
 306
 307 /// Given the span of `some_macro!(args);`, gives the span of `(` and `)`,
 308 /// and the type of (opening) delimiter used.
 309 fn find_delimiters<'tcx>(cx: &LateContext<'tcx>, span: Span) -> Option<(Span, Span, char)> {
 310     let snippet = cx.sess().parse_sess.source_map().span_to_snippet(span).ok()?;
 311     let (open, open_ch) = snippet.char_indices().find(|&(_, c)| "([{".contains(c))?;
 312     let close = snippet.rfind(|c| ")]}".contains(c))?;
 313     Some((
 314         span.from_inner(InnerSpan { start: open, end: open + 1 }),
 315         span.from_inner(InnerSpan { start: close, end: close + 1 }),
 316         open_ch,
 317     ))
 318 }
 319
 320 fn panic_call<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>) -> (Span, Symbol, Symbol) {
 321     let mut expn = f.span.ctxt().outer_expn_data();
 322
 323     let mut panic_macro = kw::Empty;
 324
 325     // Unwrap more levels of macro expansion, as panic_2015!()
 326     // was likely expanded from panic!() and possibly from
 327     // [debug_]assert!().
 328     loop {
 329         let parent = expn.call_site.ctxt().outer_expn_data();
 330         let Some(id) = parent.macro_def_id else { break };
 331         let Some(name) = cx.tcx.get_diagnostic_name(id) else { break };
 332         if !matches!(
 333             name,
 334             sym::core_panic_macro
 335                 | sym::std_panic_macro
 336                 | sym::assert_macro
 337                 | sym::debug_assert_macro
 338                 | sym::unreachable_macro
 339         ) {
 340             break;
 341         }
 342         expn = parent;
 343         panic_macro = name;
 344     }
 345
 346     let macro_symbol =
 347         if let hygiene::ExpnKind::Macro(_, symbol) = expn.kind { symbol } else { sym::panic };
 348     (expn.call_site, panic_macro, macro_symbol)
 349 }
 350
 351 fn is_arg_inside_call(arg: Span, call: Span) -> bool {
 352     // We only add suggestions if the argument we're looking at appears inside the
 353     // panic call in the source file, to avoid invalid suggestions when macros are involved.
 354     // We specifically check for the spans to not be identical, as that happens sometimes when
 355     // proc_macros lie about spans and apply the same span to all the tokens they produce.
 356     call.contains(arg) && !call.source_equal(arg)
 357 }