compiler/rustc_lint/src/non_fmt_panic.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_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("panic message is not a string literal");
 124         l.note(&format!("this usage of {}!() is deprecated; it will be a hard error in Rust 2021", symbol));
 125         l.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>");
 126         if !is_arg_inside_call(arg_span, span) {
 127             // No clue where this argument is coming from.
 128             l.emit();
 129             return;
 130         }
 131         if arg_macro.map_or(false, |id| cx.tcx.is_diagnostic_item(sym::format_macro, id)) {
 132             // A case of `panic!(format!(..))`.
 133             l.note(format!("the {}!() macro supports formatting, so there's no need for the format!() macro here", symbol).as_str());
 134             if let Some((open, close, _)) = find_delimiters(cx, arg_span) {
 135                 l.multipart_suggestion(
 136                     "remove the `format!(..)` macro call",
 137                     vec![
 138                         (arg_span.until(open.shrink_to_hi()), "".into()),
 139                         (close.until(arg_span.shrink_to_hi()), "".into()),
 140                     ],
 141                     Applicability::MachineApplicable,
 142                 );
 143             }
 144         } else {
 145             let ty = cx.typeck_results().expr_ty(arg);
 146             // If this is a &str or String, we can confidently give the `"{}", ` suggestion.
 147             let is_str = matches!(
 148                 ty.kind(),
 149                 ty::Ref(_, r, _) if *r.kind() == ty::Str,
 150             ) || matches!(
 151                 ty.ty_adt_def(),
 152                 Some(ty_def) if cx.tcx.is_diagnostic_item(sym::String, ty_def.did()),
 153             );
 154
 155             let (suggest_display, suggest_debug) = cx.tcx.infer_ctxt().enter(|infcx| {
 156                 let display = is_str || cx.tcx.get_diagnostic_item(sym::Display).map(|t| {
 157                     infcx.type_implements_trait(t, ty, InternalSubsts::empty(), cx.param_env).may_apply()
 158                 }) == Some(true);
 159                 let debug = !display && cx.tcx.get_diagnostic_item(sym::Debug).map(|t| {
 160                     infcx.type_implements_trait(t, ty, InternalSubsts::empty(), cx.param_env).may_apply()
 161                 }) == Some(true);
 162                 (display, debug)
 163             });
 164
 165             let suggest_panic_any = !is_str && panic == sym::std_panic_macro;
 166
 167             let fmt_applicability = if suggest_panic_any {
 168                 // If we can use panic_any, use that as the MachineApplicable suggestion.
 169                 Applicability::MaybeIncorrect
 170             } else {
 171                 // If we don't suggest panic_any, using a format string is our best bet.
 172                 Applicability::MachineApplicable
 173             };
 174
 175             if suggest_display {
 176                 l.span_suggestion_verbose(
 177                     arg_span.shrink_to_lo(),
 178                     "add a \"{}\" format string to Display the message",
 179                     "\"{}\", ",
 180                     fmt_applicability,
 181                 );
 182             } else if suggest_debug {
 183                 l.span_suggestion_verbose(
 184                     arg_span.shrink_to_lo(),
 185                     &format!(
 186                         "add a \"{{:?}}\" format string to use the Debug implementation of `{}`",
 187                         ty,
 188                     ),
 189                     "\"{:?}\", ",
 190                     fmt_applicability,
 191                 );
 192             }
 193
 194             if suggest_panic_any {
 195                 if let Some((open, close, del)) = find_delimiters(cx, span) {
 196                     l.multipart_suggestion(
 197                         &format!(
 198                             "{}use std::panic::panic_any instead",
 199                             if suggest_display || suggest_debug {
 200                                 "or "
 201                             } else {
 202                                 ""
 203                             },
 204                         ),
 205                         if del == '(' {
 206                             vec![(span.until(open), "std::panic::panic_any".into())]
 207                         } else {
 208                             vec![
 209                                 (span.until(open.shrink_to_hi()), "std::panic::panic_any(".into()),
 210                                 (close, ")".into()),
 211                             ]
 212                         },
 213                         Applicability::MachineApplicable,
 214                     );
 215                 }
 216             }
 217         }
 218         l.emit();
 219     });
 220 }
 221
 222 fn check_panic_str<'tcx>(
 223     cx: &LateContext<'tcx>,
 224     f: &'tcx hir::Expr<'tcx>,
 225     arg: &'tcx hir::Expr<'tcx>,
 226     fmt: &str,
 227 ) {
 228     if !fmt.contains(&['{', '}']) {
 229         // No brace, no problem.
 230         return;
 231     }
 232
 233     let (span, _, _) = panic_call(cx, f);
 234
 235     if in_external_macro(cx.sess(), span) && in_external_macro(cx.sess(), arg.span) {
 236         // Nothing that can be done about it in the current crate.
 237         return;
 238     }
 239
 240     let fmt_span = arg.span.source_callsite();
 241
 242     let (snippet, style) = match cx.sess().parse_sess.source_map().span_to_snippet(fmt_span) {
 243         Ok(snippet) => {
 244             // Count the number of `#`s between the `r` and `"`.
 245             let style = snippet.strip_prefix('r').and_then(|s| s.find('"'));
 246             (Some(snippet), style)
 247         }
 248         Err(_) => (None, None),
 249     };
 250
 251     let mut fmt_parser = Parser::new(fmt, style, snippet.clone(), false, ParseMode::Format);
 252     let n_arguments = (&mut fmt_parser).filter(|a| matches!(a, Piece::NextArgument(_))).count();
 253
 254     if n_arguments > 0 && fmt_parser.errors.is_empty() {
 255         let arg_spans: Vec<_> = match &fmt_parser.arg_places[..] {
 256             [] => vec![fmt_span],
 257             v => v
 258                 .iter()
 259                 .map(|span| fmt_span.from_inner(InnerSpan::new(span.start, span.end)))
 260                 .collect(),
 261         };
 262         cx.struct_span_lint(NON_FMT_PANICS, arg_spans, |lint| {
 263             let mut l = lint.build(match n_arguments {
 264                 1 => "panic message contains an unused formatting placeholder",
 265                 _ => "panic message contains unused formatting placeholders",
 266             });
 267             l.note("this message is not used as a format string when given without arguments, but will be in Rust 2021");
 268             if is_arg_inside_call(arg.span, span) {
 269                 l.span_suggestion(
 270                     arg.span.shrink_to_hi(),
 271                     &format!("add the missing argument{}", pluralize!(n_arguments)),
 272                     ", ...",
 273                     Applicability::HasPlaceholders,
 274                 );
 275                 l.span_suggestion(
 276                     arg.span.shrink_to_lo(),
 277                     "or add a \"{}\" format string to use the message literally",
 278                     "\"{}\", ",
 279                     Applicability::MachineApplicable,
 280                 );
 281             }
 282             l.emit();
 283         });
 284     } else {
 285         let brace_spans: Option<Vec<_>> =
 286             snippet.filter(|s| s.starts_with('"') || s.starts_with("r#")).map(|s| {
 287                 s.char_indices()
 288                     .filter(|&(_, c)| c == '{' || c == '}')
 289                     .map(|(i, _)| fmt_span.from_inner(InnerSpan { start: i, end: i + 1 }))
 290                     .collect()
 291             });
 292         let msg = match &brace_spans {
 293             Some(v) if v.len() == 1 => "panic message contains a brace",
 294             _ => "panic message contains braces",
 295         };
 296         cx.struct_span_lint(NON_FMT_PANICS, brace_spans.unwrap_or_else(|| vec![span]), |lint| {
 297             let mut l = lint.build(msg);
 298             l.note("this message is not used as a format string, but will be in Rust 2021");
 299             if is_arg_inside_call(arg.span, span) {
 300                 l.span_suggestion(
 301                     arg.span.shrink_to_lo(),
 302                     "add a \"{}\" format string to use the message literally",
 303                     "\"{}\", ",
 304                     Applicability::MachineApplicable,
 305                 );
 306             }
 307             l.emit();
 308         });
 309     }
 310 }
 311
 312 /// Given the span of `some_macro!(args);`, gives the span of `(` and `)`,
 313 /// and the type of (opening) delimiter used.
 314 fn find_delimiters<'tcx>(cx: &LateContext<'tcx>, span: Span) -> Option<(Span, Span, char)> {
 315     let snippet = cx.sess().parse_sess.source_map().span_to_snippet(span).ok()?;
 316     let (open, open_ch) = snippet.char_indices().find(|&(_, c)| "([{".contains(c))?;
 317     let close = snippet.rfind(|c| ")]}".contains(c))?;
 318     Some((
 319         span.from_inner(InnerSpan { start: open, end: open + 1 }),
 320         span.from_inner(InnerSpan { start: close, end: close + 1 }),
 321         open_ch,
 322     ))
 323 }
 324
 325 fn panic_call<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>) -> (Span, Symbol, Symbol) {
 326     let mut expn = f.span.ctxt().outer_expn_data();
 327
 328     let mut panic_macro = kw::Empty;
 329
 330     // Unwrap more levels of macro expansion, as panic_2015!()
 331     // was likely expanded from panic!() and possibly from
 332     // [debug_]assert!().
 333     loop {
 334         let parent = expn.call_site.ctxt().outer_expn_data();
 335         let Some(id) = parent.macro_def_id else { break };
 336         let Some(name) = cx.tcx.get_diagnostic_name(id) else { break };
 337         if !matches!(
 338             name,
 339             sym::core_panic_macro
 340                 | sym::std_panic_macro
 341                 | sym::assert_macro
 342                 | sym::debug_assert_macro
 343                 | sym::unreachable_macro
 344         ) {
 345             break;
 346         }
 347         expn = parent;
 348         panic_macro = name;
 349     }
 350
 351     let macro_symbol =
 352         if let hygiene::ExpnKind::Macro(_, symbol) = expn.kind { symbol } else { sym::panic };
 353     (expn.call_site, panic_macro, macro_symbol)
 354 }
 355
 356 fn is_arg_inside_call(arg: Span, call: Span) -> bool {
 357     // We only add suggestions if the argument we're looking at appears inside the
 358     // panic call in the source file, to avoid invalid suggestions when macros are involved.
 359     // We specifically check for the spans to not be identical, as that happens sometimes when
 360     // proc_macros lie about spans and apply the same span to all the tokens they produce.
 361     call.contains(arg) && !call.source_equal(arg)
 362 }