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Correct generic parameter ordering in error note for E0747 #72848

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merged 3 commits into from
Jun 3, 2020
+21 −3
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Correct generic parameter ordering in error note for E0747 #72848

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718d28c
Correct generic parameter ordering in error note
camelid Jun 1, 2020
fd76d23
Use `bug!` instead of `panic!`
camelid Jun 1, 2020
56f87ef
Include kind in `bug!`
camelid Jun 1, 2020
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18 changes: 17 additions & 1 deletion src/librustc_typeck/astconv.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
use crate::collect::PlaceholderHirTyCollector;
use crate::middle::resolve_lifetime as rl;
use crate::require_c_abi_if_c_variadic;
use rustc_ast::ast::ParamKindOrd;
use rustc_ast::util::lev_distance::find_best_match_for_name;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_errors::ErrorReported;
Expand Down Expand Up @@ -483,8 +484,23 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
arg.descr(),
kind,
);

let kind_ord = match kind {
"lifetime" => ParamKindOrd::Lifetime,
"type" => ParamKindOrd::Type,
"constant" => ParamKindOrd::Const,
_ => panic!(),
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@camelid camelid Jun 1, 2020 •
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Is this the right way to trigger an ICE?

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I believe that bug! is the preferred way to trigger an ICE.

In this case, I would recommend changing opt_span_bug_fmt to take the original GenericParamDefKind, rather than its string description. That will allow you to write an exhaustive match, removing the need for an explicit panic!/bug!

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Thanks for the tip! I'm new to contributing to rustc, so could you describe the change you're recommending in more detail?

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On closer examination, it turns out that the two callers of this function actually have two different "original" types: GenericParamDefKind and GenericArg.

I believe your change is actually perfectly correct.

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I went through the same thought process @Aaron1011. It would be a little cleaner to pass ParamKindOrd directly, but I'm not sure it's worth making more changes.

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Is it worth opening an issue?

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It would be easy to change in this pull request if desired, but I'm not sure it's worth doing: it adds quite a bit of boilerplate code, and it's only used in this one case. If we ever find ourselves doing something similar again in the future, we should revisit it.

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};
let arg_ord = match arg {
GenericArg::Lifetime(_) => ParamKindOrd::Lifetime,
GenericArg::Type(_) => ParamKindOrd::Type,
GenericArg::Const(_) => ParamKindOrd::Const,
};

// This note will be true as long as generic parameters are strictly ordered by their kind.
err.note(&format!("{} arguments must be provided before {} arguments", kind, arg.descr()));
let (first, last) =
if kind_ord < arg_ord { (kind, arg.descr()) } else { (arg.descr(), kind) };
err.note(&format!("{} arguments must be provided before {} arguments", first, last));
err.emit();
}

Expand Down
4 changes: 2 additions & 2 deletions src/test/ui/suggestions/suggest-move-types.stderr
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Expand Up @@ -124,15 +124,15 @@ error[E0747]: lifetime provided when a type was expected
LL | struct Cl<'a, 'b, 'c, T, U, V, M: ThreeWithLifetime<T, 'a, A=(), B=(), C=(), U, 'b, V, 'c>> {
| ^^
|
= note: type arguments must be provided before lifetime arguments
= note: lifetime arguments must be provided before type arguments

error[E0747]: lifetime provided when a type was expected
--> $DIR/suggest-move-types.rs:82:56
|
LL | struct Dl<'a, 'b, 'c, T, U, V, M: ThreeWithLifetime<T, 'a, A=(), B=(), U, 'b, C=(), V, 'c>> {
| ^^
|
= note: type arguments must be provided before lifetime arguments
= note: lifetime arguments must be provided before type arguments

error: aborting due to 12 previous errors

Expand Down