Detect missing fields with default values and suggest `..` #135794

estebank · 2025-01-20T21:18:53Z

When a struct ctor use has missing fields, if all those missing fields have defaults, suggest ..:

error[E0063]: missing fields `field1` and `field2` in initializer of `S`
  --> $DIR/non-exhaustive-ctor.rs:16:13
   |
LL |     let _ = S { field: () };
   |             ^ missing `field1` and `field2`
   |
help: all remaining fields have default values, you can use those values with `..`
   |
LL |     let _ = S { field: (), .. };
   |                          ++++

rustbot · 2025-01-20T21:19:02Z

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estebank · 2025-01-20T21:21:20Z

tests/ui/structs/default-field-values/non-exhaustive-ctor.stderr

+error[E0603]: unit struct `Priv` is private
+  --> $DIR/non-exhaustive-ctor.rs:23:39
+   |
+LL |     let _ = S { field: (), field1: m::Priv, field2: m::Priv };
+   |                                       ^^^^ private unit struct
+   |
+note: the unit struct `Priv` is defined here
+  --> $DIR/non-exhaustive-ctor.rs:10:5
+   |
+LL |     struct Priv;
+   |     ^^^^^^^^^^^^


This case is not relevant to this PR, but I'm looking on resolve to make it also suggest .. if Priv is private but field1 is public.

This will allow API designs where the construction of a public struct will always need .., protecting against future API breakage (in the same way that non_exhaustive is used in patterns).

jieyouxu

Thanks, I left some feedback

jieyouxu · 2025-01-21T05:08:28Z

compiler/rustc_hir_typeck/src/expr.rs

+                } else {
+                    "if your crate were nightly-only, you could add \
+                     `#![feature(default_field_values)]` to your crate and"
+                },


Discussion: we probably don't want to make the suggestion to go from a crate compilable on stable -> need nightly for this feature?

jieyouxu · 2025-01-21T05:09:42Z

tests/ui/structs/default-field-values/non-exhaustive-ctor.rs

@@ -0,0 +1,26 @@
+#![feature(default_field_values)]


Suggestion: since the suggestions are machine-applicable, could you add //@ run-rustfix or //@ rustfix-only-machine-applicable?

This was an intermediary step, I wanted to deal with the private types cases which will likely not be machine applicable, but I can split the tests instead and mark this one.

Ah ok, thats fine

jieyouxu · 2025-01-21T05:11:16Z

tests/ui/structs/default-field-values/non-exhaustive-ctor.rs

@@ -0,0 +1,26 @@
+#![feature(default_field_values)]


Discussion: also note that this test does not snapshot the other suggestion where we are nightly-only but do not have the feature gate. Maybe revision this test, but I don't think it matters that much.

I can add that.

jieyouxu · 2025-01-21T05:12:41Z

@rustbot author

When a struct definition has default field values, and the use struct ctor has missing field, if all those missing fields have defaults suggest `..`: ``` error[E0063]: missing fields `field1` and `field2` in initializer of `S` --> $DIR/non-exhaustive-ctor.rs:16:13 | LL | let _ = S { field: () }; | ^ missing `field1` and `field2` | help: all remaining fields have defaults, use `..` | LL | let _ = S { field: (), .. }; | ++++ ```

estebank · 2025-01-21T21:27:00Z

@rustbot review

estebank · 2025-01-21T21:38:49Z

Split off the parts of the test meant for privacy check into its own file (and own PR: #135846).

jieyouxu

Thanks!

jieyouxu · 2025-01-22T00:39:42Z

@bors r+ rollup

bors · 2025-01-22T00:39:45Z

📌 Commit 922e6bb has been approved by jieyouxu

It is now in the queue for this repository.

…r=jieyouxu Detect missing fields with default values and suggest `..` When a struct ctor use has missing fields, if all those missing fields have defaults, suggest `..`: ``` error[E0063]: missing fields `field1` and `field2` in initializer of `S` --> $DIR/non-exhaustive-ctor.rs:16:13 | LL | let _ = S { field: () }; | ^ missing `field1` and `field2` | help: all remaining fields have default values, you can use those values with `..` | LL | let _ = S { field: (), .. }; | ++++ ```

Rollup of 8 pull requests Successful merges: - rust-lang#135779 (CI: free disk on linux arm runner) - rust-lang#135794 (Detect missing fields with default values and suggest `..`) - rust-lang#135814 (ci: use ghcr buildkit image) - rust-lang#135818 (tests: Port `translation` to rmake.rs) - rust-lang#135823 (make UI tests that use `--test` work on panic=abort targets) - rust-lang#135837 (Remove test panic from File::open) - rust-lang#135852 (Add `AsyncFn*` to `core` prelude) - rust-lang#135856 (Library: Finalize dyn compatibility renaming) r? `@ghost` `@rustbot` modify labels: rollup

…r=jieyouxu Detect missing fields with default values and suggest `..` When a struct ctor use has missing fields, if all those missing fields have defaults, suggest `..`: ``` error[E0063]: missing fields `field1` and `field2` in initializer of `S` --> $DIR/non-exhaustive-ctor.rs:16:13 | LL | let _ = S { field: () }; | ^ missing `field1` and `field2` | help: all remaining fields have default values, you can use those values with `..` | LL | let _ = S { field: (), .. }; | ++++ ```

rustbot assigned fee1-dead Jan 20, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jan 20, 2025

estebank commented Jan 20, 2025

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jieyouxu assigned jieyouxu and unassigned fee1-dead Jan 21, 2025

jieyouxu reviewed Jan 21, 2025

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jieyouxu added A-diagnostics Area: Messages for errors, warnings, and lints F-default_field_values `#![feature(default_field_values)]` labels Jan 21, 2025

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jan 21, 2025

estebank force-pushed the non-exhaustive-dfv-ctor branch from 86e6877 to 922e6bb Compare January 21, 2025 21:26

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jan 21, 2025

estebank mentioned this pull request Jan 21, 2025

Tracking issue for RFC 3681: Default field values #132162

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jieyouxu approved these changes Jan 22, 2025

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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-review Status: Awaiting review from the assignee but also interested parties. labels Jan 22, 2025

jieyouxu mentioned this pull request Jan 22, 2025

Rollup of 8 pull requests #135861

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jieyouxu mentioned this pull request Jan 22, 2025

Rollup of 7 pull requests #135868

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Detect missing fields with default values and suggest `..` #135794

Detect missing fields with default values and suggest `..` #135794

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Detect missing fields with default values and suggest .. #135794

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Detect missing fields with default values and suggest `..` #135794

Detect missing fields with default values and suggest `..` #135794