Reject extra fields in MGCA struct const arguments by Shourya742 · Pull Request #157886 · rust-lang/rust

Shourya742 · 2026-06-14T12:29:04Z

rustbot · 2026-06-14T12:29:07Z

HIR ty lowering was modified

rustbot · 2026-06-14T12:29:09Z

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Shourya742 · 2026-06-14T12:32:03Z

+        for init in inits {
+            if !variant_def.fields.iter().any(|field_def| field_def.name == init.field.name) {
+                let err = tcx.dcx().struct_span_err(
+                    init.field.span,
+                    format!("struct expression has no field named `{}`", init.field),
+                );
+                return ty::Const::new_error(tcx, err.emit());
+            }
+        }
+


Currently, lower_const_arg_struct handled missing and duplicate initializers, but it did not check for extra fields. This checkd for fields that do not exist on the target variant.

View changes since the review

camelid · 2026-06-15T00:48:35Z

+            if !variant_def.fields.iter().any(|field_def| field_def.name == init.field.name) {
+                let err = tcx.dcx().struct_span_err(
+                    init.field.span,
+                    format!("struct expression has no field named `{}`", init.field),


This message seems a little off... the expression does have the field; it's the struct definition that does not. We should match the wording for the normal (non-MGCA) message: "struct S has no field named x".

View changes since the review

hmm.. Now I think of it, should have not written expressions. I will update it, Thanks.

Added here: 5f70f22

camelid · 2026-06-16T15:01:13Z

                let err = tcx.dcx().struct_span_err(
                    init.field.span,
-                    format!("struct expression has no field named `{}`", init.field),
+                    format!("struct {} has no field named `{}`", variant_def.name, init.field),


This should use backticks around the struct name, like the non-MGCA error message I showed before.

Also, please add a test with an enum struct variant (like enum E { S {} }) so we can make sure that message looks good too. You will probably have to change the message for enums, so we that can match the non-MGCA error message for that too: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=ce981a7c73a8b0d5322b9bd9f9bd628d

Otherwise, this looks good!

View changes since the review

Ah, my bad, I didn't see the backticks.

I don't think we need the enum case, since it doesn't ICE and already provides a clear error message for enum. Apparently, this ICE's only for struct variants.

Ok, but please still add a test for enum variants so we can at least track the message. After that, r=me

Added here: 325f881

rust-log-analyzer · 2026-06-17T01:49:58Z

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

fmt: checked 6923 files
tidy check
tidy [rustdoc_json (src)]: `rustdoc-json-types` modified, checking format version
tidy: Skipping binary file check, read-only filesystem
tidy [style (tests)]: /checkout/tests/ui/const-generics/mgca/adt_expr_unit_enum_extra_field.rs: missing trailing newline
tidy [style (tests)]: FAIL
removing old virtual environment
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'venv'
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'virtualenv'
Requirement already satisfied: pip in ./build/venv/lib/python3.10/site-packages (26.1.1)
Collecting pip
---
info: ✓ ES-Check passed! All files are ES10 compatible.
typechecking javascript files
tidy: The following check failed: style (tests)
Bootstrap failed while executing `test src/tools/tidy tidyselftest --extra-checks=py,cpp,js,spellcheck`
Command `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/rust-tidy --root-path=/checkout --cargo-path=/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo --output-dir=/checkout/obj/build --concurrency=4 --npm-path=/node/bin/yarn --ci=true --extra-checks=py,cpp,js,spellcheck` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1624:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1511:29

--- BACKTRACE vvv
   0: <bootstrap::utils::exec::DeferredCommand>::finish_process
             at /checkout/src/bootstrap/src/utils/exec.rs:939:17
   1: <bootstrap::utils::exec::DeferredCommand>::wait_for_output::<&bootstrap::utils::exec::ExecutionContext>
             at /checkout/src/bootstrap/src/utils/exec.rs:831:21
   2: <bootstrap::utils::exec::ExecutionContext>::run
             at /checkout/src/bootstrap/src/utils/exec.rs:741:45
   3: <bootstrap::utils::exec::BootstrapCommand>::run::<&bootstrap::core::builder::Builder>
             at /checkout/src/bootstrap/src/utils/exec.rs:339:27
   4: <bootstrap::core::build_steps::test::Tidy as bootstrap::core::builder::Step>::run
             at /checkout/src/bootstrap/src/core/build_steps/test.rs:1511:29
   5: <bootstrap::core::builder::Builder>::ensure::<bootstrap::core::build_steps::test::Tidy>
             at /checkout/src/bootstrap/src/core/builder/mod.rs:1596:36
   6: <bootstrap::core::build_steps::test::Tidy as bootstrap::core::builder::Step>::make_run
             at /checkout/src/bootstrap/src/core/build_steps/test.rs:1433:21
   7: <bootstrap::core::builder::StepDescription>::maybe_run
             at /checkout/src/bootstrap/src/core/builder/mod.rs:476:13
   8: bootstrap::core::builder::cli_paths::match_paths_to_steps_and_run
             at /checkout/src/bootstrap/src/core/builder/cli_paths.rs:232:18
   9: <bootstrap::core::builder::Builder>::run_step_descriptions
             at /checkout/src/bootstrap/src/core/builder/mod.rs:1139:9
  10: <bootstrap::core::builder::Builder>::execute_cli
             at /checkout/src/bootstrap/src/core/builder/mod.rs:1118:14
  11: <bootstrap::Build>::build
             at /checkout/src/bootstrap/src/lib.rs:803:25
  12: bootstrap::main
             at /checkout/src/bootstrap/src/bin/main.rs:130:11
  13: <fn() as core::ops::function::FnOnce<()>>::call_once
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/core/src/ops/function.rs:250:5
  14: std::sys::backtrace::__rust_begin_short_backtrace::<fn(), ()>
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/std/src/sys/backtrace.rs:166:18
  15: std::rt::lang_start::<()>::{closure#0}
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/std/src/rt.rs:206:18
  16: <&dyn core::ops::function::Fn<(), Output = i32> + core::marker::Sync + core::panic::unwind_safe::RefUnwindSafe as core::ops::function::FnOnce<()>>::call_once
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/core/src/ops/function.rs:287:21
  17: std::panicking::catch_unwind::do_call::<&dyn core::ops::function::Fn<(), Output = i32> + core::marker::Sync + core::panic::unwind_safe::RefUnwindSafe, i32>
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/std/src/panicking.rs:581:40
  18: std::panicking::catch_unwind::<i32, &dyn core::ops::function::Fn<(), Output = i32> + core::marker::Sync + core::panic::unwind_safe::RefUnwindSafe>
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/std/src/panicking.rs:544:19
  19: std::panic::catch_unwind::<&dyn core::ops::function::Fn<(), Output = i32> + core::marker::Sync + core::panic::unwind_safe::RefUnwindSafe, i32>
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/std/src/panic.rs:359:14
  20: std::rt::lang_start_internal::{closure#0}
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/std/src/rt.rs:175:24
  21: std::panicking::catch_unwind::do_call::<std::rt::lang_start_internal::{closure#0}, isize>
             at /rustc/0417c25868d6dfbd1c291dfeae950504faa6f790/library/std/src/panicking.rs:581:40
---
  28: __libc_start_main
  29: _start


Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:02:46
  local time: Wed Jun 17 01:49:48 UTC 2026
  network time: Wed, 17 Jun 2026 01:49:49 GMT
##[error]Process completed with exit code 1.
##[group]Run echo "disk usage:"

Shourya742 added 2 commits June 14, 2026 17:55

add test to show extra field in mgca adt const arg

8da99a0

make sure check if there are extra fields or not.

86efd4b

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 Jun 14, 2026

rustbot assigned davidtwco Jun 14, 2026

rustbot assigned BoxyUwU and unassigned davidtwco Jun 14, 2026

Shourya742 commented Jun 14, 2026

View reviewed changes

camelid reviewed Jun 15, 2026

View reviewed changes

camelid assigned camelid and unassigned BoxyUwU Jun 15, 2026

Shourya742 requested a review from camelid June 16, 2026 13:29

camelid reviewed Jun 16, 2026

View reviewed changes

improve diagnostics and mentions struct and not expression

84b803e

rust-cloud-vms Bot force-pushed the 2026-06-14-reject-extra-field-mgca-adt-const branch from 5f70f22 to 84b803e Compare June 16, 2026 17:07

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rust-cloud-vms Bot force-pushed the 2026-06-14-reject-extra-field-mgca-adt-const branch from 325f881 to a55c9f6 Compare June 17, 2026 00:52

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add adt_expr_unit_enum_extra-field test

89b62af

rust-cloud-vms Bot force-pushed the 2026-06-14-reject-extra-field-mgca-adt-const branch from a55c9f6 to 89b62af Compare June 17, 2026 01:35

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