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Improve panic_fmt message for panic!("{}") with a fmt placeholder.

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This commit is contained in:
Mara Bos 2020-10-18 23:25:06 +02:00
parent 451c9864c4
commit ded269fa10
1 changed files with 45 additions and 17 deletions
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62
compiler/rustc_lint/src/panic_fmt.rs
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@ -47,24 +47,52 @@ impl<'tcx> LateLintPass<'tcx> for PanicFmt {
fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tcx hir::Expr<'tcx>) {
if let hir::ExprKind::Lit(lit) = &arg.kind {
if let ast::LitKind::Str(sym, _) = lit.node {
if sym.as_str().contains(&['{', '}'][..]) {
let expn = f.span.ctxt().outer_expn_data();
if let Some(id) = expn.macro_def_id {
if cx.tcx.is_diagnostic_item(sym::std_panic_macro, id)
|| cx.tcx.is_diagnostic_item(sym::core_panic_macro, id)
{
let expn = {
// Unwrap another level of macro expansion if this
// panic!() was expanded from assert!().
let parent = expn.call_site.ctxt().outer_expn_data();
if parent.macro_def_id.map_or(false, |id| {
cx.tcx.is_diagnostic_item(sym::assert_macro, id)
}) {
parent
} else {
expn
let s = sym.as_str();
let open = s.find('{');
let close = s[open.unwrap_or(0)..].find('}');
let looks_like_placeholder = match (open, close) {
(Some(_), Some(_)) => true,
(Some(_), None) | (None, Some(_)) => false,
(None, None) => return // OK, no braces.
};
let expn = f.span.ctxt().outer_expn_data();
if let Some(id) = expn.macro_def_id {
if cx.tcx.is_diagnostic_item(sym::std_panic_macro, id)
|| cx.tcx.is_diagnostic_item(sym::core_panic_macro, id)
{
let expn = {
// Unwrap another level of macro expansion if this
// panic!() was expanded from assert!().
let parent = expn.call_site.ctxt().outer_expn_data();
if parent.macro_def_id.map_or(false, |id| {
cx.tcx.is_diagnostic_item(sym::assert_macro, id)
}) {
parent
} else {
expn
}
};
if looks_like_placeholder {
cx.struct_span_lint(PANIC_FMT, arg.span.source_callsite(), |lint| {
let mut l = lint.build("Panic message contains an unused formatting placeholder");
l.note("This message is not used as a format string when given without arguments, but will be in a future Rust version");
if expn.call_site.contains(arg.span) {
l.span_suggestion(
arg.span.shrink_to_hi(),
"add the missing argument(s)",
", argument".into(),
Applicability::HasPlaceholders,
);
l.span_suggestion(
arg.span.shrink_to_lo(),
"or add a \"{}\" format string to use the message literally",
"\"{}\", ".into(),
Applicability::MaybeIncorrect,
);
}
};
l.emit();
});
} else {
cx.struct_span_lint(PANIC_FMT, expn.call_site, |lint| {
let mut l = lint.build("Panic message contains a brace");
l.note("This message is not used as a format string, but will be in a future Rust version");