Fix AnonConst ICE #91312

terrarier2111 · 2021-11-28T09:42:53Z

I am not sure if this is even the correct place to fix this issue, but i went down the path where the generic args came from and i wasn't able to find a clear cause for this down there. But if anybody has a suggestion what i should do, just tell me.
This fixes: #91267

rust-highfive · 2021-11-28T09:42:55Z

r? @jackh726

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terrarier2111 · 2021-11-28T09:44:07Z

compiler/rustc_typeck/src/collect/type_of.rs

-                    | Node::TraitRef(&TraitRef { path, .. }) => &*path,
+                    | Node::TraitRef(&TraitRef { path, .. }) => {
+                        // Check for empty generic args, because if there are no generic args, this would otherwise ICE
+                        if path.segments.len() == 1


Not sure if == 1 is correct here or if checking for < 2 would be better.

Checking for the length of the segment does prevent the unwrap triggered ICE in this test case, but this doesn't seem like the best way to prevent similar ICEs. I think something like 0: u8<e::f<5>=e::f> should also trigger an ICE after your fixes.

Obviously this fuzzer generated example is really contrived, but to prevent this type of ICE, the most reasonable change to me seems to be to shift the code here, which tries to find the arg_index and segment from the path, to this pattern arm and not call unwrap on the result, but just return None if this fails to find any arg_index. Maybe try to minimize code duplication here.

I'm not sure about the other pattern arms, maybe calling unwrap on the resulting path for those branches could also ICE and maybe we should never call unwrap in the first place.

First of all thanks for the feedback, i'll look into applying the changes you suggested.
(btw 0: u8<e::f<5>=e::f> doesn't panic at all neither on stable nor with my changed)

What about 0: u8<e<5>=e::f>?

Stable panics, with my changes it doesn't.

I just mean that without knowing more about this code that it makes more sense to assume that the person who inserted that unwrap probably had a good reason for including it.

So, i looked into it and i didn't find any case in which it could cause problems
Disclaimer: I am relatively new to rustc development, so maybe i missed something.

@jackh726 what are your thoughts on this?

Right, so I guess in this case u8<e<5>=e> is treated as type ascription for the 0?

I think the right thing here is to change the unwrap_or_else(|| bug!()) here to a delay_span_bug ("no arg matching AnonConst in path") and a return None.

Right, so i applied your suggestions, I had to add another variable cuz i can't return the None value in the unwrap_or_else, also the test output didn't change

terrarier2111 · 2021-11-28T09:45:21Z

compiler/rustc_typeck/src/collect/type_of.rs

+                    | Node::TraitRef(&TraitRef { path, .. }) => {
+                        // Check for empty generic args, because if there are no generic args, this would otherwise ICE
+                        if path.segments.len() == 1
+                            && path.segments[0].args.map_or(-1, |x| x.args.len() as isize) == 0


Not sure if None should be handled the same as len == 0.

terrarier2111 · 2021-11-28T09:47:38Z

Also I am not sure if this is the correct way or if I should replace the bug! in line 194 with return None;

jackh726 · 2021-12-01T22:30:42Z

compiler/rustc_typeck/src/collect/type_of.rs

-                    | Node::TraitRef(&TraitRef { path, .. }) => &*path,
+                    | Node::TraitRef(&TraitRef { path, .. }) => {
+                        // Check for empty generic args, because if there are no generic args, this would otherwise ICE
+                        if path.segments.len() == 1


Right, so I guess in this case u8<e<5>=e> is treated as type ascription for the 0?

I think the right thing here is to change the unwrap_or_else(|| bug!()) here to a delay_span_bug ("no arg matching AnonConst in path") and a return None.

jackh726 · 2021-12-04T16:35:53Z

compiler/rustc_typeck/src/collect/type_of.rs

+                        .delay_span_bug(tcx.def_span(def_id), "no arg matching AnonConst in path");
+                    return None;
+                }
+                let (arg_index, segment) = filtered.unwrap();


Can you use a match with the above condition too?

jackh726 · 2021-12-05T22:35:10Z

When you fix formatting, can you also squash commits?

Add test Apply suggestions Switch to match Apply cargofmt

terrarier2111 · 2021-12-06T17:04:51Z

When you fix formatting, can you also squash commits?

Done

jackh726 · 2021-12-06T17:08:39Z

@bors r+ rollup

bors · 2021-12-06T17:09:00Z

📌 Commit a0fb992 has been approved by jackh726

…kh726 Fix AnonConst ICE I am not sure if this is even the correct place to fix this issue, but i went down the path where the generic args came from and i wasn't able to find a clear cause for this down there. But if anybody has a suggestion what i should do, just tell me. This fixes: rust-lang#91267

…askrgr Rollup of 10 pull requests Successful merges: - rust-lang#87614 (Recommend fix `count()` -> `len()` on slices) - rust-lang#91065 (Add test for evaluate_obligation: Ok(EvaluatedToOkModuloRegions) ICE) - rust-lang#91312 (Fix AnonConst ICE) - rust-lang#91341 (Add `array::IntoIter::{empty, from_raw_parts}`) - rust-lang#91493 (Remove a dead code path.) - rust-lang#91503 (Tweak "call this function" suggestion to have smaller span) - rust-lang#91547 (Suggest try_reserve in try_reserve_exact) - rust-lang#91562 (Pretty print async block without redundant space) - rust-lang#91620 (Update books) - rust-lang#91622 (:arrow_up: rust-analyzer) Failed merges: - rust-lang#91571 (Remove unneeded access to pretty printer's `s` field in favor of deref) r? `@ghost` `@rustbot` modify labels: rollup

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Fix AnonConst ICE

a0fb992

Add test Apply suggestions Switch to match Apply cargofmt

terrarier2111 force-pushed the anon-const-ice branch from 4bf421a to a0fb992 Compare December 6, 2021 17:03

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 6, 2021

matthiaskrgr mentioned this pull request Dec 6, 2021

Rollup of 9 pull requests #91602

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matthiaskrgr mentioned this pull request Dec 7, 2021

Rollup of 9 pull requests #91621

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matthiaskrgr mentioned this pull request Dec 7, 2021

Rollup of 10 pull requests #91627

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bors merged commit 57ae43d into rust-lang:master Dec 7, 2021

rustbot added this to the 1.59.0 milestone Dec 7, 2021

lcnr added the A-const-generics Area: const generics (parameters and arguments) label Dec 11, 2021

lcnr mentioned this pull request Dec 11, 2021

Tracking issue for const generics (RFC 2000) #44580

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Fix AnonConst ICE #91312

Fix AnonConst ICE #91312

terrarier2111 commented Nov 28, 2021 •

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Fix AnonConst ICE #91312

Fix AnonConst ICE #91312

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