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Auto merge of #97456 - Bryysen:issue-97319-fix, r=compiler-errors

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Improve error message for E0081

Closes #97319
This commit is contained in:
bors 2022-05-29 12:00:30 +00:00
commit abc7681a76
9 changed files with 174 additions and 76 deletions
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51
compiler/rustc_typeck/src/check/check.rs
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@ -1376,6 +1376,8 @@ fn check_enum<'tcx>(
}
let mut disr_vals: Vec<Discr<'tcx>> = Vec::with_capacity(vs.len());
// This tracks the previous variant span (in the loop) incase we need it for diagnostics
let mut prev_variant_span: Span = DUMMY_SP;
for ((_, discr), v) in iter::zip(def.discriminants(tcx), vs) {
// Check for duplicate discriminant values
if let Some(i) = disr_vals.iter().position(|&x| x.val == discr.val) {
@ -1390,42 +1392,59 @@ fn check_enum<'tcx>(
Some(ref expr) => tcx.hir().span(expr.hir_id),
None => v.span,
};
let display_discr = display_discriminant_value(tcx, v, discr.val);
let display_discr_i = display_discriminant_value(tcx, variant_i, disr_vals[i].val);
struct_span_err!(
let display_discr = format_discriminant_overflow(tcx, v, discr);
let display_discr_i = format_discriminant_overflow(tcx, variant_i, disr_vals[i]);
let no_disr = v.disr_expr.is_none();
let mut err = struct_span_err!(
tcx.sess,
span,
sp,
E0081,
"discriminant value `{}` already exists",
discr.val,
)
.span_label(i_span, format!("first use of {display_discr_i}"))
.span_label(span, format!("enum already has {display_discr}"))
.emit();
"discriminant value `{}` assigned more than once",
discr,
);
err.span_label(i_span, format!("first assignment of {display_discr_i}"));
err.span_label(span, format!("second assignment of {display_discr}"));
if no_disr {
err.span_label(
prev_variant_span,
format!(
"assigned discriminant for `{}` was incremented from this discriminant",
v.ident
),
);
}
err.emit();
}
disr_vals.push(discr);
prev_variant_span = v.span;
}
check_representable(tcx, sp, def_id);
check_transparent(tcx, sp, def);
}
/// Format an enum discriminant value for use in a diagnostic message.
fn display_discriminant_value<'tcx>(
/// In the case that a discriminant is both a duplicate and an overflowing literal,
/// we insert both the assigned discriminant and the literal it overflowed from into the formatted
/// output. Otherwise we format the discriminant normally.
fn format_discriminant_overflow<'tcx>(
tcx: TyCtxt<'tcx>,
variant: &hir::Variant<'_>,
evaluated: u128,
dis: Discr<'tcx>,
) -> String {
if let Some(expr) = &variant.disr_expr {
let body = &tcx.hir().body(expr.body).value;
if let hir::ExprKind::Lit(lit) = &body.kind
&& let rustc_ast::LitKind::Int(lit_value, _int_kind) = &lit.node
&& evaluated != *lit_value
&& dis.val != *lit_value
{
return format!("`{evaluated}` (overflowed from `{lit_value}`)");
return format!("`{dis}` (overflowed from `{lit_value}`)");
}
}
format!("`{}`", evaluated)
format!("`{dis}`")
}
pub(super) fn check_type_params_are_used<'tcx>(