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 `non_fmt_panic` lint detects `panic!("..")` with `{` or `}` in the string literal
  11     /// when it is not used as a format string.
  12     ///
  13     /// ### Example
  14     ///
  15     /// ```rust,no_run
  16     /// panic!("{}");
  17     /// ```
  18     ///
  19     /// {{produces}}
  20     ///
  21     /// ### Explanation
  22     ///
  23     /// `panic!("{}")` panics with the message `"{}"`, as a `panic!()` invocation
  24     /// with a single argument does not use `format_args!()`.
  25     /// A future edition of Rust will interpret this string as format string,
  26     /// which would break this.
  27     NON_FMT_PANIC,
  28     Warn,
  29     "detect braces in single-argument panic!() invocations",
  30     report_in_external_macro
  31 }
  32
  33 declare_lint_pass!(PanicFmt => [NON_FMT_PANIC]);
  34
  35 impl<'tcx> LateLintPass<'tcx> for PanicFmt {
  36     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
  37         if let hir::ExprKind::Call(f, [arg]) = &expr.kind {
  38             if let &ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(f).kind() {
  39                 if Some(def_id) == cx.tcx.lang_items().begin_panic_fn()
  40                     || Some(def_id) == cx.tcx.lang_items().panic_fn()
  41                 {
  42                     check_panic(cx, f, arg);
  43                 }
  44             }
  45         }
  46     }
  47 }
  48
  49 fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tcx hir::Expr<'tcx>) {
  50     if let hir::ExprKind::Lit(lit) = &arg.kind {
  51         if let ast::LitKind::Str(sym, _) = lit.node {
  52             let mut expn = f.span.ctxt().outer_expn_data();
  53             if let Some(id) = expn.macro_def_id {
  54                 if cx.tcx.is_diagnostic_item(sym::std_panic_macro, id)
  55                     || cx.tcx.is_diagnostic_item(sym::core_panic_macro, id)
  56                 {
  57                     let fmt = sym.as_str();
  58                     if !fmt.contains(&['{', '}'][..]) {
  59                         return;
  60                     }
  61
  62                     let fmt_span = arg.span.source_callsite();
  63
  64                     let (snippet, style) =
  65                         match cx.sess().parse_sess.source_map().span_to_snippet(fmt_span) {
  66                             Ok(snippet) => {
  67                                 // Count the number of `#`s between the `r` and `"`.
  68                                 let style = snippet.strip_prefix('r').and_then(|s| s.find('"'));
  69                                 (Some(snippet), style)
  70                             }
  71                             Err(_) => (None, None),
  72                         };
  73
  74                     let mut fmt_parser =
  75                         Parser::new(fmt.as_ref(), style, snippet.clone(), false, ParseMode::Format);
  76                     let n_arguments =
  77                         (&mut fmt_parser).filter(|a| matches!(a, Piece::NextArgument(_))).count();
  78
  79                     // Unwrap another level of macro expansion if this panic!()
  80                     // was expanded from assert!() or debug_assert!().
  81                     for &assert in &[sym::assert_macro, sym::debug_assert_macro] {
  82                         let parent = expn.call_site.ctxt().outer_expn_data();
  83                         if parent
  84                             .macro_def_id
  85                             .map_or(false, |id| cx.tcx.is_diagnostic_item(assert, id))
  86                         {
  87                             expn = parent;
  88                         }
  89                     }
  90
  91                     if n_arguments > 0 && fmt_parser.errors.is_empty() {
  92                         let arg_spans: Vec<_> = match &fmt_parser.arg_places[..] {
  93                             [] => vec![fmt_span],
  94                             v => v.iter().map(|span| fmt_span.from_inner(*span)).collect(),
  95                         };
  96                         cx.struct_span_lint(NON_FMT_PANIC, arg_spans, |lint| {
  97                             let mut l = lint.build(match n_arguments {
  98                                 1 => "panic message contains an unused formatting placeholder",
  99                                 _ => "panic message contains unused formatting placeholders",
 100                             });
 101                             l.note("this message is not used as a format string when given without arguments, but will be in a future Rust edition");
 102                             if expn.call_site.contains(arg.span) {
 103                                 l.span_suggestion(
 104                                     arg.span.shrink_to_hi(),
 105                                     &format!("add the missing argument{}", pluralize!(n_arguments)),
 106                                     ", ...".into(),
 107                                     Applicability::HasPlaceholders,
 108                                 );
 109                                 l.span_suggestion(
 110                                     arg.span.shrink_to_lo(),
 111                                     "or add a \"{}\" format string to use the message literally",
 112                                     "\"{}\", ".into(),
 113                                     Applicability::MachineApplicable,
 114                                 );
 115                             }
 116                             l.emit();
 117                         });
 118                     } else {
 119                         let brace_spans: Option<Vec<_>> = snippet
 120                             .filter(|s| s.starts_with('"') || s.starts_with("r#"))
 121                             .map(|s| {
 122                                 s.char_indices()
 123                                     .filter(|&(_, c)| c == '{' || c == '}')
 124                                     .map(|(i, _)| {
 125                                         fmt_span.from_inner(InnerSpan { start: i, end: i + 1 })
 126                                     })
 127                                     .collect()
 128                             });
 129                         let msg = match &brace_spans {
 130                             Some(v) if v.len() == 1 => "panic message contains a brace",
 131                             _ => "panic message contains braces",
 132                         };
 133                         cx.struct_span_lint(NON_FMT_PANIC, brace_spans.unwrap_or(vec![expn.call_site]), |lint| {
 134                             let mut l = lint.build(msg);
 135                             l.note("this message is not used as a format string, but will be in a future Rust edition");
 136                             if expn.call_site.contains(arg.span) {
 137                                 l.span_suggestion(
 138                                     arg.span.shrink_to_lo(),
 139                                     "add a \"{}\" format string to use the message literally",
 140                                     "\"{}\", ".into(),
 141                                     Applicability::MachineApplicable,
 142                                 );
 143                             }
 144                             l.emit();
 145                         });
 146                     }
 147                 }
 148             }
 149         }
 150     }
 151 }