On method chain expression failure, look for missing method in earlier segments of the chain #115229

iSwapna · 2023-08-25T22:20:46Z

This PR tries to fix the issue: #115222

As suggested by @estebank , I did the following:

Add new test tests/ui/structs/method-chain-expression-failure.rs
In compiler/rusct_hir_tycheck/src/method/suggest.rs
walking up the method chain and calling probe_for_name with the method name. But the call fails to return Ok.

rustbot · 2023-08-25T22:20:53Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @wesleywiser (or someone else) soon.

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compiler/rustc_hir_typeck/src/method/suggest.rs

oli-obk · 2023-09-11T07:31:14Z

r? @oli-obk

Please include some high level information about this PR in the main message (e.g. link to the issue and state what new message you are adding to which existing message)

oli-obk · 2023-09-11T07:32:20Z

it looks like there are tests other than yours that are affected by this change. If you bless all ui tests, you should see some changes in your git status view

compiler/rustc_hir_typeck/src/method/suggest.rs

iSwapna · 2023-09-11T15:59:48Z

@rustbot review

tests/ui/typeck/issue-31173.stderr

compiler/rustc_hir_typeck/src/method/suggest.rs

oli-obk · 2023-09-13T15:26:01Z

r? @estebank

iSwapna · 2023-09-16T06:47:45Z

@estebank Contents of tests/ui/structs/method-chain-expression-failure.stdout:

Applicable candidates: [(Candidate { xform_self_ty: &A, xform_ret_ty: Some(B), item: AssocItem { def_id: DefId(0:12 ~ method_chain_expression_failure[2e39]::{impl#0}::b), name:\
 "b", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [] }, \
Match)]
Applicable candidates: [(Candidate { xform_self_ty: &B, xform_ret_ty: Some(C), item: AssocItem { def_id: DefId(0:14 ~ method_chain_expression_failure[2e39]::{impl#1}::c), name:\
 "c", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [] }, \
Match)]
Applicable candidates: [(Candidate { xform_self_ty: &C, xform_ret_ty: Some(D), item: AssocItem { def_id: DefId(0:17 ~ method_chain_expression_failure[2e39]::{impl#2}::d), name:\
 "d", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [] }, \
Match)]
prev_ty: &C
item_name: foo
No Match
prev_ty: &B
item_name: foo
self_ty=&B probe=Candidate { xform_self_ty: &B, xform_ret_ty: Some(()), item: AssocItem { def_id: DefId(0:15 ~ method_chain_expression_failure[2e39]::{impl#1}::foo), name: "foo\
", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [] }
1705 :: Consider_probe: comparing return_ty &B with xform ret ty ()
Error Type is Err(Sorts(ExpectedFound { expected: &B, found: () }))
Applicable candidates: [(Candidate { xform_self_ty: &B, xform_ret_ty: Some(()), item: AssocItem { def_id: DefId(0:15 ~ method_chain_expression_failure[2e39]::{impl#1}::foo), na\
me: "foo", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [\
] }, BadReturnType)]
BadReturnType
prev_ty: &A
item_name: foo
No Match

iSwapna · 2023-09-16T06:51:41Z

@estebank Contents of tests/ui/structs/method-chain-expression-failure.stdout:

Applicable candidates: [(Candidate { xform_self_ty: &A, xform_ret_ty: Some(B), item: AssocItem { def_id: DefId(0:12 ~ method_chain_expression_failure[2e39]::{impl#0}::b), name:\
 "b", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [] }, \
Match)]
Applicable candidates: [(Candidate { xform_self_ty: &B, xform_ret_ty: Some(C), item: AssocItem { def_id: DefId(0:14 ~ method_chain_expression_failure[2e39]::{impl#1}::c), name:\
 "c", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [] }, \
Match)]
Applicable candidates: [(Candidate { xform_self_ty: &C, xform_ret_ty: Some(D), item: AssocItem { def_id: DefId(0:17 ~ method_chain_expression_failure[2e39]::{impl#2}::d), name:\
 "d", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [] }, \
Match)]
prev_ty: &C
item_name: foo
No Match
prev_ty: &B
item_name: foo
self_ty=&B probe=Candidate { xform_self_ty: &B, xform_ret_ty: Some(()), item: AssocItem { def_id: DefId(0:15 ~ method_chain_expression_failure[2e39]::{impl#1}::foo), name: "foo\
", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [] }
1705 :: Consider_probe: comparing return_ty &B with xform ret ty ()
Error Type is Err(Sorts(ExpectedFound { expected: &B, found: () }))
Applicable candidates: [(Candidate { xform_self_ty: &B, xform_ret_ty: Some(()), item: AssocItem { def_id: DefId(0:15 ~ method_chain_expression_failure[2e39]::{impl#1}::foo), na\
me: "foo", kind: Fn, container: ImplContainer, trait_item_def_id: None, fn_has_self_parameter: true, opt_rpitit_info: None }, kind: InherentImplCandidate([], []), import_ids: [\
] }, BadReturnType)]
BadReturnType
prev_ty: &A
item_name: foo
No Match

In this case, should we check for return type of foo() to match the one implemented by B ? If so, we should first check if there is a variable the return value is getting assigned to? But I think, since this is a hint to the user, just matching by name and returning the first (closest to D) one as a possible match would be enough to point the user in the right direction?

estebank · 2023-09-19T01:00:50Z

But I think, since this is a hint to the user, just matching by name and returning the first (closest to D) one as a possible match would be enough to point the user in the right direction?

If we can filter the method with the right return type, I would prefer to suggest it, otherwise I would mention all of them. Give me a minute to check the rest of the PR and correlate with the logs you have here.

estebank · 2023-09-19T01:09:42Z

Ah! I see what's happening. A.b().c().d().foo(); as written of course fails, but the solution in this case is to write A.b().foo();, but the logic as written is (somewhat incorrectly) trying to figure out if A.b().foo().c().d(); is valid. The former is a case of additional elements in the chain, while the later is a case of misplaced method call. I think we can support both with high accuracy. For the latter the current logic we need to make a change: if you look at return_ty being &B it means that it's looking for a method that will return prev_ty, not just one that has that as Self. I'll point it out inline.

compiler/rustc_hir_typeck/src/method/suggest.rs

estebank · 2023-11-06T18:16:56Z

compiler/rustc_hir_typeck/src/method/suggest.rs

+                    prev_ty,
+                    rcvr_expr.hir_id,
+                    ProbeScope::TraitsInScope,) {
+                        err.span_label(method_span, format!("{item_kind} `{item_name}` is available on `{prev_ty}`"));


If you use parent_expr.span, it would make the error be correct, but when you have more than one element in the chain you would end up with overlapping spans which won't look great.

An option we have is to iterate once using the while let as you have it now, but collect the messages and spans in a vec and emit the diagnostics afterwards by iterating over the vec and peeking at the next span.

estebank · 2023-11-06T18:17:37Z

compiler/rustc_hir_typeck/src/method/suggest.rs

+        // Only if an appropriate error source is not found, check method chain for possible candiates
+        let error_source_not_found = unsatisfied_predicates.is_empty();
+        if error_source_not_found && let Mode::MethodCall = mode && let SelfSource::MethodCall(mut rcvr_expr) = source {
+        while let hir::ExprKind::MethodCall(_path_segment, parent_expr, _args, method_span) =


I would prefer we called parent_expr to something that includes rcvr/receiver in the name, because the parent concept is highly overloaded :)

estebank · 2023-11-06T18:18:37Z

tests/ui/structs/method-chain-expression-failure.stderr

+LL |     A.b().c().d().foo();
+   |           ---     ^^^ method not found in `D`
+   |           |
+   |           method `foo` is available on `&B`


To drive the point home, if you look at the impl the span label should be pointing at the .b() which returns B and not at the method call .c() which returns C.

estebank

I love the results so far! On your next change, please squash your commits as I don't think we need the prior attempts anymore and expect us to land this shortly.

estebank · 2023-11-07T19:49:24Z

You'll need to run x.py test tests/ui --bless again. Let's also squash the remaining commits and I think we can merge the PR after that.

compiler/rustc_hir_typeck/src/method/suggest.rs

iSwapna · 2023-11-10T06:51:13Z

You'll need to run x.py test tests/ui --bless again. Let's also squash the remaining commits and I think we can merge the PR after that.

Had found an issue. Done now.

…s receiver to align spans

estebank · 2023-11-10T21:09:20Z

@bors r+

bors · 2023-11-10T21:09:23Z

📌 Commit 56a109d has been approved by estebank

It is now in the queue for this repository.

bors · 2023-11-10T21:10:32Z

⌛ Testing commit 56a109d with merge edf0b1d...

bors · 2023-11-10T23:06:13Z

☀️ Test successful - checks-actions
Approved by: estebank
Pushing edf0b1d to master...

rust-timer · 2023-11-11T04:29:16Z

Finished benchmarking commit (edf0b1d): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

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	mean	range	count
Regressions ❌ (primary)	0.9%	[0.5%, 1.3%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-1.0%, -0.4%]	8
Improvements ✅ (secondary)	-4.2%	[-4.2%, -4.2%]	1
All ❌✅ (primary)	-0.1%	[-1.0%, 1.3%]	12

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	mean	range	count
Regressions ❌ (primary)	0.5%	[0.4%, 0.5%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.4%, 0.5%]	3

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Bootstrap: 674.395s -> 675.48s (0.16%)
Artifact size: 311.13 MiB -> 311.11 MiB (-0.01%)

rustbot assigned wesleywiser Aug 25, 2023

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iSwapna commented Sep 10, 2023

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On method chain expression failure, look for missing method in earlier segments of the chain #115222

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estebank changed the title ~~Issue 115222 fix~~ On method chain expression failure, look for missing method in earlier segments of the chain Sep 11, 2023

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iSwapna force-pushed the issue-115222-fix branch from acf08eb to d7214df Compare November 5, 2023 05:52

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iSwapna force-pushed the issue-115222-fix branch 2 times, most recently from 763194d to 7441d1e Compare November 10, 2023 06:49

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Recurse over the method chain and maintain a stack to peek at previou…

56a109d

…s receiver to align spans

iSwapna force-pushed the issue-115222-fix branch from 7441d1e to 56a109d Compare November 10, 2023 21:01

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On method chain expression failure, look for missing method in earlier segments of the chain #115229

On method chain expression failure, look for missing method in earlier segments of the chain #115229

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On method chain expression failure, look for missing method in earlier segments of the chain #115229

On method chain expression failure, look for missing method in earlier segments of the chain #115229

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