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_middle::ty;
   6 use rustc_parse_format::{ParseMode, Parser, Piece};
   7 use rustc_session::lint::FutureIncompatibilityReason;
   8 use rustc_span::edition::Edition;
   9 use rustc_span::{hygiene, sym, symbol::kw, symbol::SymbolStr, InnerSpan, Span, Symbol};
  10
  11 declare_lint! {
  12     /// The `non_fmt_panics` lint detects `panic!(..)` invocations where the first
  13     /// argument is not a formatting string.
  14     ///
  15     /// ### Example
  16     ///
  17     /// ```rust,no_run
  18     /// panic!("{}");
  19     /// panic!(123);
  20     /// ```
  21     ///
  22     /// {{produces}}
  23     ///
  24     /// ### Explanation
  25     ///
  26     /// In Rust 2018 and earlier, `panic!(x)` directly uses `x` as the message.
  27     /// That means that `panic!("{}")` panics with the message `"{}"` instead
  28     /// of using it as a formatting string, and `panic!(123)` will panic with
  29     /// an `i32` as message.
  30     ///
  31     /// Rust 2021 always interprets the first argument as format string.
  32     NON_FMT_PANICS,
  33     Warn,
  34     "detect single-argument panic!() invocations in which the argument is not a format string",
  35     @future_incompatible = FutureIncompatibleInfo {
  36         reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
  37         explain_reason: false,
  38     };
  39     report_in_external_macro
  40 }
  41
  42 declare_lint_pass!(NonPanicFmt => [NON_FMT_PANICS]);
  43
  44 impl<'tcx> LateLintPass<'tcx> for NonPanicFmt {
  45     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
  46         if let hir::ExprKind::Call(f, [arg]) = &expr.kind {
  47             if let &ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(f).kind() {
  48                 if Some(def_id) == cx.tcx.lang_items().begin_panic_fn()
  49                     || Some(def_id) == cx.tcx.lang_items().panic_fn()
  50                     || Some(def_id) == cx.tcx.lang_items().panic_str()
  51                 {
  52                     if let Some(id) = f.span.ctxt().outer_expn_data().macro_def_id {
  53                         if cx.tcx.is_diagnostic_item(sym::std_panic_2015_macro, id)
  54                             || cx.tcx.is_diagnostic_item(sym::core_panic_2015_macro, id)
  55                         {
  56                             check_panic(cx, f, arg);
  57                         }
  58                     }
  59                 }
  60             }
  61         }
  62     }
  63 }
  64
  65 fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tcx hir::Expr<'tcx>) {
  66     if let hir::ExprKind::Lit(lit) = &arg.kind {
  67         if let ast::LitKind::Str(sym, _) = lit.node {
  68             // The argument is a string literal.
  69             check_panic_str(cx, f, arg, &sym.as_str());
  70             return;
  71         }
  72     }
  73
  74     // The argument is *not* a string literal.
  75
  76     let (span, panic, symbol_str) = panic_call(cx, f);
  77
  78     // Find the span of the argument to `panic!()`, before expansion in the
  79     // case of `panic!(some_macro!())`.
  80     // We don't use source_callsite(), because this `panic!(..)` might itself
  81     // be expanded from another macro, in which case we want to stop at that
  82     // expansion.
  83     let mut arg_span = arg.span;
  84     let mut arg_macro = None;
  85     while !span.contains(arg_span) {
  86         let expn = arg_span.ctxt().outer_expn_data();
  87         if expn.is_root() {
  88             break;
  89         }
  90         arg_macro = expn.macro_def_id;
  91         arg_span = expn.call_site;
  92     }
  93
  94     cx.struct_span_lint(NON_FMT_PANICS, arg_span, |lint| {
  95         let mut l = lint.build("panic message is not a string literal");
  96         l.note("this usage of panic!() is deprecated; it will be a hard error in Rust 2021");
  97         l.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>");
  98         if !span.contains(arg_span) {
  99             // No clue where this argument is coming from.
 100             l.emit();
 101             return;
 102         }
 103         if arg_macro.map_or(false, |id| cx.tcx.is_diagnostic_item(sym::format_macro, id)) {
 104             // A case of `panic!(format!(..))`.
 105             l.note(format!("the {}!() macro supports formatting, so there's no need for the format!() macro here", symbol_str).as_str());
 106             if let Some((open, close, _)) = find_delimiters(cx, arg_span) {
 107                 l.multipart_suggestion(
 108                     "remove the `format!(..)` macro call",
 109                     vec![
 110                         (arg_span.until(open.shrink_to_hi()), "".into()),
 111                         (close.until(arg_span.shrink_to_hi()), "".into()),
 112                     ],
 113                     Applicability::MachineApplicable,
 114                 );
 115             }
 116         } else {
 117             l.span_suggestion_verbose(
 118                 arg_span.shrink_to_lo(),
 119                 "add a \"{}\" format string to Display the message",
 120                 "\"{}\", ".into(),
 121                 Applicability::MaybeIncorrect,
 122             );
 123             if panic == sym::std_panic_macro {
 124                 if let Some((open, close, del)) = find_delimiters(cx, span) {
 125                     l.multipart_suggestion(
 126                         "or use std::panic::panic_any instead",
 127                         if del == '(' {
 128                             vec![(span.until(open), "std::panic::panic_any".into())]
 129                         } else {
 130                             vec![
 131                                 (span.until(open.shrink_to_hi()), "std::panic::panic_any(".into()),
 132                                 (close, ")".into()),
 133                             ]
 134                         },
 135                         Applicability::MachineApplicable,
 136                     );
 137                 }
 138             }
 139         }
 140         l.emit();
 141     });
 142 }
 143
 144 fn check_panic_str<'tcx>(
 145     cx: &LateContext<'tcx>,
 146     f: &'tcx hir::Expr<'tcx>,
 147     arg: &'tcx hir::Expr<'tcx>,
 148     fmt: &str,
 149 ) {
 150     if !fmt.contains(&['{', '}'][..]) {
 151         // No brace, no problem.
 152         return;
 153     }
 154
 155     let fmt_span = arg.span.source_callsite();
 156
 157     let (snippet, style) = match cx.sess().parse_sess.source_map().span_to_snippet(fmt_span) {
 158         Ok(snippet) => {
 159             // Count the number of `#`s between the `r` and `"`.
 160             let style = snippet.strip_prefix('r').and_then(|s| s.find('"'));
 161             (Some(snippet), style)
 162         }
 163         Err(_) => (None, None),
 164     };
 165
 166     let mut fmt_parser =
 167         Parser::new(fmt.as_ref(), style, snippet.clone(), false, ParseMode::Format);
 168     let n_arguments = (&mut fmt_parser).filter(|a| matches!(a, Piece::NextArgument(_))).count();
 169
 170     let (span, _, _) = panic_call(cx, f);
 171
 172     if n_arguments > 0 && fmt_parser.errors.is_empty() {
 173         let arg_spans: Vec<_> = match &fmt_parser.arg_places[..] {
 174             [] => vec![fmt_span],
 175             v => v.iter().map(|span| fmt_span.from_inner(*span)).collect(),
 176         };
 177         cx.struct_span_lint(NON_FMT_PANICS, arg_spans, |lint| {
 178             let mut l = lint.build(match n_arguments {
 179                 1 => "panic message contains an unused formatting placeholder",
 180                 _ => "panic message contains unused formatting placeholders",
 181             });
 182             l.note("this message is not used as a format string when given without arguments, but will be in Rust 2021");
 183             if span.contains(arg.span) {
 184                 l.span_suggestion(
 185                     arg.span.shrink_to_hi(),
 186                     &format!("add the missing argument{}", pluralize!(n_arguments)),
 187                     ", ...".into(),
 188                     Applicability::HasPlaceholders,
 189                 );
 190                 l.span_suggestion(
 191                     arg.span.shrink_to_lo(),
 192                     "or add a \"{}\" format string to use the message literally",
 193                     "\"{}\", ".into(),
 194                     Applicability::MachineApplicable,
 195                 );
 196             }
 197             l.emit();
 198         });
 199     } else {
 200         let brace_spans: Option<Vec<_>> =
 201             snippet.filter(|s| s.starts_with('"') || s.starts_with("r#")).map(|s| {
 202                 s.char_indices()
 203                     .filter(|&(_, c)| c == '{' || c == '}')
 204                     .map(|(i, _)| fmt_span.from_inner(InnerSpan { start: i, end: i + 1 }))
 205                     .collect()
 206             });
 207         let msg = match &brace_spans {
 208             Some(v) if v.len() == 1 => "panic message contains a brace",
 209             _ => "panic message contains braces",
 210         };
 211         cx.struct_span_lint(NON_FMT_PANICS, brace_spans.unwrap_or_else(|| vec![span]), |lint| {
 212             let mut l = lint.build(msg);
 213             l.note("this message is not used as a format string, but will be in Rust 2021");
 214             if span.contains(arg.span) {
 215                 l.span_suggestion(
 216                     arg.span.shrink_to_lo(),
 217                     "add a \"{}\" format string to use the message literally",
 218                     "\"{}\", ".into(),
 219                     Applicability::MachineApplicable,
 220                 );
 221             }
 222             l.emit();
 223         });
 224     }
 225 }
 226
 227 /// Given the span of `some_macro!(args);`, gives the span of `(` and `)`,
 228 /// and the type of (opening) delimiter used.
 229 fn find_delimiters<'tcx>(cx: &LateContext<'tcx>, span: Span) -> Option<(Span, Span, char)> {
 230     let snippet = cx.sess().parse_sess.source_map().span_to_snippet(span).ok()?;
 231     let (open, open_ch) = snippet.char_indices().find(|&(_, c)| "([{".contains(c))?;
 232     let close = snippet.rfind(|c| ")]}".contains(c))?;
 233     Some((
 234         span.from_inner(InnerSpan { start: open, end: open + 1 }),
 235         span.from_inner(InnerSpan { start: close, end: close + 1 }),
 236         open_ch,
 237     ))
 238 }
 239
 240 fn panic_call<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>) -> (Span, Symbol, SymbolStr) {
 241     let mut expn = f.span.ctxt().outer_expn_data();
 242
 243     let mut panic_macro = kw::Empty;
 244
 245     // Unwrap more levels of macro expansion, as panic_2015!()
 246     // was likely expanded from panic!() and possibly from
 247     // [debug_]assert!().
 248     for &i in
 249         &[sym::std_panic_macro, sym::core_panic_macro, sym::assert_macro, sym::debug_assert_macro]
 250     {
 251         let parent = expn.call_site.ctxt().outer_expn_data();
 252         if parent.macro_def_id.map_or(false, |id| cx.tcx.is_diagnostic_item(i, id)) {
 253             expn = parent;
 254             panic_macro = i;
 255         }
 256     }
 257
 258     let macro_symbol =
 259         if let hygiene::ExpnKind::Macro(_, symbol) = expn.kind { symbol } else { sym::panic };
 260     (expn.call_site, panic_macro, macro_symbol.as_str())
 261 }