Move generic arg/param validation to `create_substs_for_generic_args` to resolve various const generics issues #68434

varkor · 2020-01-21T23:09:39Z

This changes some diagnostics, but I think they're around as helpful as the previous ones, and occur infrequently regardless.

Fixes #68257.
Fixes #68398.

r? @eddyb

rust-highfive · 2020-01-21T23:09:43Z

Some changes occurred in diagnostic error codes

cc @GuillaumeGomez

eddyb

LGTM, but I'd like a second opinion from @rust-lang/compiler (and maybe we need a check-mode crater run? I doubt it though)

src/librustc_typeck/astconv.rs

src/librustc/ty/structural_impls.rs

src/librustc_typeck/astconv.rs

estebank · 2020-01-24T22:19:09Z

src/librustc_typeck/astconv.rs

+            arg.descr(),
+            kind,
+        )
+        .emit();


No reordering suggestion for this case?

I'd rather leave this PR for the bug-fixes and follow up with the diagnostics improvements. That's a good follow up, though.

varkor · 2020-01-25T22:25:56Z

r? @nikomatsakis for a second opinion (#68434 (review))

eddyb · 2020-01-25T23:02:54Z

src/librustc_typeck/astconv.rs

+                    explicit_lifetimes = Err(GenericArgCountMismatch(Some(ErrorReported)));
                    let mut err = tcx.sess.struct_span_err(span, msg);
                    err.span_note(span_late, note);
                    err.emit();


@Centril @estebank Can we make it so you have to emit an error to get an ErrorReported token, and maybe make it unconstructible except by the diagnostic reporting machinery?

Oh, that'd be cute. :)

Are we tracking this anywhere?

Don't think so.

Created #69426.

yodaldevoid · 2020-02-02T04:17:14Z

Is this PR waiting on anything specific?

varkor · 2020-02-02T10:23:14Z

@yodaldevoid: a second reviewer's opinion on the PR.

bors · 2020-02-06T19:09:06Z

☔ The latest upstream changes (presumably #68893) made this pull request unmergeable. Please resolve the merge conflicts.

nikomatsakis

I didn't follow 100% of what's going on here, but it overall seems pretty reasonable -- except that I think the new errors are kind of confusingly worded. Am I missing something?

src/librustc_typeck/astconv.rs

nikomatsakis · 2020-02-14T17:41:53Z

src/test/ui/generic/generic-arg-mismatch-recover.rs

@@ -4,7 +4,6 @@ struct Bar<'a>(&'a ());

 fn main() {
    Foo::<'static, 'static, ()>(&0); //~ ERROR wrong number of lifetime arguments


why does this error go away?

Previously if we encountered an incorrect generic argument, we would just try to skip it and continue going: https://github.com/rust-lang/rust/pull/68434/files#diff-1b4d50b82a87f1031cd5f99b64123de7L578. Now we just stop checking the remaining arguments, because there's a high likelihood the remaining arguments are invalid and we'd just spit out lots of errors that aren't particularly helpful.

nikomatsakis · 2020-02-14T17:43:11Z

src/librustc_typeck/astconv.rs

+                    (Some(generic_args), infer_args)
+                } else {
+                    // The last component of this tuple is unimportant.
+                    (None, false)


(Annoying, it'd be nice to change this to a custom enum -- but obviously pre-existing for this PR.)

nikomatsakis · 2020-02-14T17:51:48Z

src/test/ui/suggestions/suggest-move-types.stderr

@@ -74,29 +74,30 @@ LL | struct Dl<'a, 'b, 'c, T, U, V, M: ThreeWithLifetime<T, 'a, A=(), B=(), U, '
   |                                                            |     this associated type binding should be moved after the generic parameters
   |                                                            this associated type binding should be moved after the generic parameters

-error: lifetime arguments must be declared prior to type arguments
-  --> $DIR/suggest-move-types.rs:34:46
+error[E0747]: type provided when a lifetime was expected


I find this error quite a bit more confusing than the old one. It suggests to me that the fix is to change T into a lifetime -- but that won't help.

I'm not quite sure what the "mental model" is that we are trying to convey to users.

I'm convinced we should be suggesting the correct order in all of these cases.

The reason I changed this is because there isn't really a restriction on the order of generic arguments: the restriction is on generic parameters, but generic arguments must match the order of generic parameters. The fact that lifetime arguments must precede type arguments is a side-effect of the parameter order. I'll try tweaking the wording to improve this. As @estebank says, ideally we'd suggest the correct order, but I'd like to get this merged sooner rather than later, as I don't know how much time I'll have for more elaborate changes now.

OK, I see. I still find the message more confusing than the old one, but perhaps I now better understand what this PR is aiming for.

nikomatsakis · 2020-02-14T18:02:14Z

src/librustc_typeck/astconv.rs

+                    explicit_lifetimes = Err(GenericArgCountMismatch(Some(ErrorReported)));
                    let mut err = tcx.sess.struct_span_err(span, msg);
                    err.span_note(span_late, note);
                    err.emit();


Oh, that'd be cute. :)

src/librustc_error_codes/error_codes/E0747.md

src/test/ui/const-generics/const-param-after-const-literal-arg.rs

src/test/ui/const-generics/const-param-before-other-params.rs

estebank · 2020-02-14T19:15:50Z

src/test/ui/suggestions/suggest-move-types.stderr

@@ -74,29 +74,30 @@ LL | struct Dl<'a, 'b, 'c, T, U, V, M: ThreeWithLifetime<T, 'a, A=(), B=(), U, '
   |                                                            |     this associated type binding should be moved after the generic parameters
   |                                                            this associated type binding should be moved after the generic parameters

-error: lifetime arguments must be declared prior to type arguments
-  --> $DIR/suggest-move-types.rs:34:46
+error[E0747]: type provided when a lifetime was expected


I'm convinced we should be suggesting the correct order in all of these cases.

…l error

varkor · 2020-02-22T02:38:23Z

@nikomatsakis: I've addressed the code comments, and also added a note to the error messages making them as descriptive as the previous ones. I'll open an issue for suggesting the correct order of all provided arguments: I'd rather split it out into a separate PR than conflate it with this one.

nikomatsakis · 2020-02-25T19:20:11Z

@bors r+

thanks, @varkor

bors · 2020-02-25T19:20:12Z

📌 Commit bead79e has been approved by nikomatsakis

bors · 2020-02-27T18:38:26Z

⌛ Testing commit bead79e with merge 6d69cab...

bors · 2020-02-27T21:56:22Z

☀️ Test successful - checks-azure
Approved by: nikomatsakis
Pushing 6d69cab to master...

rust-highfive · 2020-02-27T21:57:29Z

📣 Toolstate changed by #68434!

Tested on commit 6d69cab.
Direct link to PR: #68434

🎉 book on windows: test-fail → test-pass (cc @carols10cents @steveklabnik).

@carols10cents

Tested on commit rust-lang/rust@6d69cab. Direct link to PR: <rust-lang/rust#68434> 🎉 book on windows: test-fail → test-pass (cc @carols10cents @steveklabnik).

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Improve generic arg–param mismatch errors #68437

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ICE when type parameter and const generic are in wrong order #68868

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varkor added 4 commits February 22, 2020 00:28

Refactor create_substs_for_generic_args a little

c9b7b1f

Make return value of check_generic_arg_count semantically clearer

dff64eb

Use Result instead of bool throughout

104131c

Be explicit about whether GenericArgCountMismatch arose from a fata…

33143fd

…l error

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varkor added 3 commits February 22, 2020 11:34

Add invalid argument spans to GenericArgCountMismatch

76fb26b

Expand the documentation for E0747

e372ad4

Add note regarding argument ordering

bead79e

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varkor mentioned this pull request Feb 24, 2020

Make emitting an error necessary to acquire a ErrorReported token #69426

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bors added the merged-by-bors This PR was explicitly merged by bors. label Feb 27, 2020

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This was referenced Feb 27, 2020

Create E0748 error code for unterminated raw strings #69260

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Accept Enum::<Param>::Variant {} over Enum::Variant::<Param> {} #69363

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JohnTitor mentioned this pull request Feb 28, 2020

ICE w/ default generic type parameter and const parameter #67858

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Tracking issue for const generics (RFC 2000) #44580

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thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0' #89868

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Move generic arg/param validation to `create_substs_for_generic_args` to resolve various const generics issues #68434

Move generic arg/param validation to `create_substs_for_generic_args` to resolve various const generics issues #68434

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		@@ -4,7 +4,6 @@ struct Bar<'a>(&'a ());

		fn main() {
		Foo::<'static, 'static, ()>(&0); //~ ERROR wrong number of lifetime arguments

Move generic arg/param validation to create_substs_for_generic_args to resolve various const generics issues #68434

Move generic arg/param validation to create_substs_for_generic_args to resolve various const generics issues #68434

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Move generic arg/param validation to `create_substs_for_generic_args` to resolve various const generics issues #68434

Move generic arg/param validation to `create_substs_for_generic_args` to resolve various const generics issues #68434

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