Add ability to attach custom #[on_unimplemented] error messages for unimplemented traits #20889

Manishearth · 2015-01-10T19:25:25Z

fixes #20783

r? @nikomatsakis

nikomatsakis · 2015-01-10T19:27:48Z

👯

ghost · 2015-01-10T21:02:59Z

Awesome :] This should be very useful.

sfackler · 2015-01-10T21:23:46Z

Cool!

flaper87 · 2015-01-10T21:51:20Z

looks better now, I think we should have an get_attr in ty but it can be left for a separate PR.

@nikomatsakis your call now :)

huonw · 2015-01-11T00:18:50Z

src/librustc/middle/traits/error_reporting.rs

+    let mut report = None;
+    ty::each_attr(infcx.tcx, def_id, |item| {
+        if item.check_name("on_unimplemented") {
+            match item.meta().node {


This pair of nested matchs can be if let Some(ref i) = item.value_str() { ... }.

huonw · 2015-01-11T00:22:25Z

Yay!

I wonder if we need to have a definition-site verification as well as the use-site behaviour, as it stands one will only get validation that the on_unimplemented message is valid when actually triggering an unimplemented error; that is, downstream users will get error messages about the invalidity of the format string.

E.g. AFAICT, this will compile fine in isolation

#[on_unimplemented = "foo {X}, {Y}, {unclosed"]
pub trait Foo {}

Manishearth · 2015-01-11T02:31:32Z

@huonw fixed the other issues

ftxqxd · 2015-01-11T02:46:16Z

It's great to see this! But I think the error message should still mention the specific trait (FromIterator in this case) somewhere, to show the actual reason why it doesn't work (and thus help towards resolving the error if the user is able to implement FromIterator for that type). That could either be done manually inside the specific #[on_unimplemented] attribute invocation or the attribute's behaviour could be changed in the compiler to add a help message instead of replacing the original error message. I personally don't have much of a preference either way.

Manishearth · 2015-01-11T02:51:31Z

@P1start It is done manually, a {Self} placeholder can be used (see the fake "FromIterator" in the test)

Manishearth · 2015-01-11T02:52:46Z

Oh, wait, I see, you want a placeholder for the trait name. I guess that can be done manually (or I can add a {trait} format arg, though that's just equivalent to directly writing path::to::Trait<{A}, {B}, {C}>). Got any idea for what the error for FromIterator should look like?

…nimplemented traits (fixes rust-lang#20783)

Manishearth · 2015-01-11T04:21:01Z

@huon I made it a note, and added a lint/test.

…utes

huonw · 2015-01-11T06:46:39Z

src/librustc/middle/traits/error_reporting.rs

@@ -88,12 +154,20 @@ pub fn report_selection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
                        infcx.resolve_type_vars_if_possible(trait_predicate);
                    if !trait_predicate.references_error() {
                        let trait_ref = trait_predicate.to_poly_trait_ref();
+                        // Check if it has a custom "#[on_unimplemented]" error message,
+                        // report with that message if it does
+                        let custom_note = report_on_unimplemented(infcx, &*trait_ref.0);


This is probably best run after the main error message, just in case the span_errs inside it are triggered, so that the output has a slightly more sensible order.

Ms2ger · 2015-01-11T13:22:22Z

src/librustc/middle/traits/error_reporting.rs

+                        let custom_note = report_on_unimplemented(infcx, &*trait_ref.0,
+                                                                  obligation.cause.span);
+                        if let Some(s) = custom_note {
+                           infcx.tcx.sess.span_note(


Indentation

nikomatsakis · 2015-01-11T20:07:54Z

src/test/compile-fail/on-unimplemented-bad-anno.rs

+
+#[rustc_on_unimplemented = "Unimplemented trait error on `{Self}` with params `<{A},{B},{C}>`"]
+//~^ ERROR there is no type parameter C on trait BadAnnotation2
+trait BadAnnotation2<A,B> {}


Maybe add a test with an illegal thing, like {}?

@nikomatsakis

fixes #20783 r? @nikomatsakis

rust-highfive assigned nikomatsakis Jan 10, 2015

Manishearth force-pushed the trait-error branch 2 times, most recently from 6665642 to 6f0419f Compare January 10, 2015 20:53

Manishearth force-pushed the trait-error branch from 6f0419f to 6cde8cf Compare January 10, 2015 21:03

huonw reviewed Jan 11, 2015
View reviewed changes

Manishearth force-pushed the trait-error branch from 6cde8cf to c671926 Compare January 11, 2015 02:29

Manishearth force-pushed the trait-error branch from c671926 to de683c4 Compare January 11, 2015 02:40

Add ability to attach custom #[on_unimplemented] error messages for u…

4d17fba

…nimplemented traits (fixes rust-lang#20783)

Manishearth force-pushed the trait-error branch 2 times, most recently from 82295a3 to dc0de42 Compare January 11, 2015 04:20

Add lint and test for malformed but unused #[on_unimplemented] attrib…

dc0de42

…utes

huonw reviewed Jan 11, 2015
View reviewed changes

Manishearth added 2 commits January 11, 2015 16:41

Make errors allow for cross-crate issues

e183277

Move error to typeck::check

add20bb

Ms2ger reviewed Jan 11, 2015
View reviewed changes

Rename #[on_unimplemented] -> #[rustc_on_unimplemented]

dd074ab

Manishearth force-pushed the trait-error branch from f0e6e8d to ad7e33e Compare January 11, 2015 18:30

Feature gate #[rustc_on_unimplemented]

ad7e33e

nikomatsakis reviewed Jan 11, 2015
View reviewed changes

Manishearth force-pushed the trait-error branch 2 times, most recently from 2f5767f to 02d0a8b Compare January 11, 2015 20:14

docs

02d0a8b

bors added a commit that referenced this pull request Jan 12, 2015

auto merge of #20889 : Manishearth/rust/trait-error, r=nikomatsakis

0aec4db

fixes #20783 r? @nikomatsakis

bors merged commit 02d0a8b into rust-lang:master Jan 12, 2015

Manishearth deleted the trait-error branch January 12, 2015 06:46

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Add ability to attach custom #[on_unimplemented] error messages for unimplemented traits #20889

Add ability to attach custom #[on_unimplemented] error messages for unimplemented traits #20889

Manishearth commented Jan 10, 2015

nikomatsakis commented Jan 10, 2015

ghost commented Jan 10, 2015

sfackler commented Jan 10, 2015

flaper87 commented Jan 10, 2015

huonw Jan 11, 2015

huonw commented Jan 11, 2015

Manishearth commented Jan 11, 2015

ftxqxd commented Jan 11, 2015

Manishearth commented Jan 11, 2015

Manishearth commented Jan 11, 2015

Manishearth commented Jan 11, 2015

huonw Jan 11, 2015

Ms2ger Jan 11, 2015

nikomatsakis Jan 11, 2015

Add ability to attach custom #[on_unimplemented] error messages for unimplemented traits #20889

Add ability to attach custom #[on_unimplemented] error messages for unimplemented traits #20889

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Manishearth commented Jan 10, 2015

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