Repository: rust
Issue: Regression: duplicate messages appear in --error-format=json
Labels: P-medium,T-compiler,regression-from-stable-to-stable,A-incr-comp,C-bug

```toml
# Cargo.toml

[package]
name = "repro"
version = "0.0.0"
edition = "2021"

[lib]
proc-macro = true
```

```rust
// src/main.rs

repro::repro!();

fn main() {}
```

```rust
// src/lib.rs

use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree};

#[proc_macro]
pub fn repro(_input: TokenStream) -> TokenStream {
    TokenStream::from_iter([
        // fn f<T: Sized>() {}
        TokenTree::Ident(Ident::new("fn", Span::call_site())),
        TokenTree::Ident(Ident::new("f", Span::call_site())),
        TokenTree::Punct(Punct::new('<', Spacing::Alone)),
        TokenTree::Ident(Ident::new("T", Span::call_site())),
        TokenTree::Punct(Punct::new(':', Spacing::Alone)),
        TokenTree::Ident(Ident::new("Sized", Span::call_site())),
        TokenTree::Punct(Punct::new('>', Spacing::Alone)),
        TokenTree::Group(Group::new(Delimiter::Parenthesis, TokenStream::new())),
        TokenTree::Group(Group::new(Delimiter::Brace, TokenStream::new())),
        // fn g() { f::<str>() }
        TokenTree::Ident(Ident::new("fn", Span::call_site())),
        TokenTree::Ident(Ident::new("g", Span::call_site())),
        TokenTree::Group(Group::new(Delimiter::Parenthesis, TokenStream::new())),
        TokenTree::Group(Group::new(
            Delimiter::Brace,
            TokenStream::from_iter([
                TokenTree::Ident(Ident::new("f", Span::call_site())),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Punct(Punct::new(':', Spacing::Alone)),
                TokenTree::Punct(Punct::new('<', Spacing::Alone)),
                TokenTree::Ident(Ident::new("str", Span::call_site())),
                TokenTree::Punct(Punct::new('>', Spacing::Alone)),
                TokenTree::Group(Group::new(Delimiter::Parenthesis, TokenStream::new())),
            ]),
        )),
        // fn h() { f::<str>() }
        TokenTree::Ident(Ident::new("fn", Span::call_site())),
        TokenTree::Ident(Ident::new("h", Span::call_site())),
        TokenTree::Group(Group::new(Delimiter::Parenthesis, TokenStream::new())),
        TokenTree::Group(Group::new(
            Delimiter::Brace,
            TokenStream::from_iter([
                TokenTree::Ident(Ident::new("f", Span::call_site())),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Punct(Punct::new(':', Spacing::Alone)),
                TokenTree::Punct(Punct::new('<', Spacing::Alone)),
                TokenTree::Ident(Ident::new("str", Span::call_site())),
                TokenTree::Punct(Punct::new('>', Spacing::Alone)),
                TokenTree::Group(Group::new(Delimiter::Parenthesis, TokenStream::new())),
            ]),
        )),
    ])
}
```

```console
$ cargo clean; cargo +nightly-2023-01-02 check --message-format=json
{"reason":"compiler-artifact","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["proc-macro"],"crate_types":["proc-macro"],"name":"repro","src_path":"/git/repro/src/lib.rs","edition":"2021","doc":true,"doctest":true,"test":true},"profile":{"opt_level":"0","debuginfo":2,"debug_assertions":true,"overflow_checks":true,"test":false},"features":[],"filenames":["/git/repro/target/debug/deps/librepro-c697fecae630a328.rmeta"],"executable":null,"fresh":false}
{"reason":"compiler-artifact","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["proc-macro"],"crate_types":["proc-macro"],"name":"repro","src_path":"/git/repro/src/lib.rs","edition":"2021","doc":true,"doctest":true,"test":true},"profile":{"opt_level":"0","debuginfo":2,"debug_assertions":true,"overflow_checks":true,"test":false},"features":[],"filenames":["/git/repro/target/debug/deps/librepro-433aa5011bfe20c0.so"],"executable":null,"fresh":false}
{"reason":"compiler-message","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"repro","src_path":"/git/repro/src/main.rs","edition":"2021","doc":true,"doctest":false,"test":true},"message":{"rendered":"error[E0277]: the size for values of type `str` cannot be known at compilation time\n --> src/main.rs:3:1\n  |\n3 | repro::repro!();\n  | ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time\n  |\n  = help: the trait `Sized` is not implemented for `str`\nnote: required by a bound in `f`\n --> src/main.rs:3:1\n  |\n3 | repro::repro!();\n  | ^^^^^^^^^^^^^^^ required by this bound in `f`\n  = note: this error originates in the macro `repro::repro` (in Nightly builds, run with -Z macro-backtrace for more info)\n\n","children":[{"children":[],"code":null,"level":"help","message":"the trait `Sized` is not implemented for `str`","rendered":null,"spans":[]},{"children":[],"code":null,"level":"note","message":"required by a bound in `f`","rendered":null,"spans":[{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":{"def_site_span":{"byte_end":167,"byte_start":119,"column_end":49,"column_start":1,"expansion":null,"file_name":"/git/repro/src/lib.rs","is_primary":false,"label":null,"line_end":6,"line_start":6,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":49,"highlight_start":1,"text":"pub fn repro(_input: TokenStream) -> TokenStream {"}]},"macro_decl_name":"repro::repro!","span":{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":null,"file_name":"src/main.rs","is_primary":false,"label":null,"line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}},"file_name":"src/main.rs","is_primary":true,"label":"required by this bound in `f`","line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}]}],"code":{"code":"E0277","explanation":"You tried to use a type which doesn't implement some trait in a place which\nexpected that trait.\n\nErroneous code example:\n\n```compile_fail,E0277\n// here we declare the Foo trait with a bar method\ntrait Foo {\n    fn bar(&self);\n}\n\n// we now declare a function which takes an object implementing the Foo trait\nfn some_func<T: Foo>(foo: T) {\n    foo.bar();\n}\n\nfn main() {\n    // we now call the method with the i32 type, which doesn't implement\n    // the Foo trait\n    some_func(5i32); // error: the trait bound `i32 : Foo` is not satisfied\n}\n```\n\nIn order to fix this error, verify that the type you're using does implement\nthe trait. Example:\n\n```\ntrait Foo {\n    fn bar(&self);\n}\n\n// we implement the trait on the i32 type\nimpl Foo for i32 {\n    fn bar(&self) {}\n}\n\nfn some_func<T: Foo>(foo: T) {\n    foo.bar(); // we can now use this method since i32 implements the\n               // Foo trait\n}\n\nfn main() {\n    some_func(5i32); // ok!\n}\n```\n\nOr in a generic context, an erroneous code example would look like:\n\n```compile_fail,E0277\nfn some_func<T>(foo: T) {\n    println!(\"{:?}\", foo); // error: the trait `core::fmt::Debug` is not\n                           //        implemented for the type `T`\n}\n\nfn main() {\n    // We now call the method with the i32 type,\n    // which *does* implement the Debug trait.\n    some_func(5i32);\n}\n```\n\nNote that the error here is in the definition of the generic function. Although\nwe only call it with a parameter that does implement `Debug`, the compiler\nstill rejects the function. It must work with all possible input types. In\norder to make this example compile, we need to restrict the generic type we're\naccepting:\n\n```\nuse std::fmt;\n\n// Restrict the input type to types that implement Debug.\nfn some_func<T: fmt::Debug>(foo: T) {\n    println!(\"{:?}\", foo);\n}\n\nfn main() {\n    // Calling the method is still fine, as i32 implements Debug.\n    some_func(5i32);\n\n    // This would fail to compile now:\n    // struct WithoutDebug;\n    // some_func(WithoutDebug);\n}\n```\n\nRust only looks at the signature of the called function, as such it must\nalready specify all requirements that will be used for every type parameter.\n"},"level":"error","message":"the size for values of type `str` cannot be known at compilation time","spans":[{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":{"def_site_span":{"byte_end":167,"byte_start":119,"column_end":49,"column_start":1,"expansion":null,"file_name":"/git/repro/src/lib.rs","is_primary":false,"label":null,"line_end":6,"line_start":6,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":49,"highlight_start":1,"text":"pub fn repro(_input: TokenStream) -> TokenStream {"}]},"macro_decl_name":"repro::repro!","span":{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":null,"file_name":"src/main.rs","is_primary":false,"label":null,"line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}},"file_name":"src/main.rs","is_primary":true,"label":"doesn't have a size known at compile-time","line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}]}}
{"reason":"compiler-message","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"repro","src_path":"/git/repro/src/main.rs","edition":"2021","doc":true,"doctest":false,"test":true},"message":{"rendered":"error: aborting due to previous error\n\n","children":[],"code":null,"level":"error","message":"aborting due to previous error","spans":[]}}
{"reason":"compiler-message","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"repro","src_path":"/git/repro/src/main.rs","edition":"2021","doc":true,"doctest":false,"test":true},"message":{"rendered":"For more information about this error, try `rustc --explain E0277`.\n","children":[],"code":null,"level":"failure-note","message":"For more information about this error, try `rustc --explain E0277`.","spans":[]}}
{"reason":"build-finished","success":false}
```

```console
$ cargo clean; cargo +nightly-2023-01-03 check --message-format=json
{"reason":"compiler-artifact","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["proc-macro"],"crate_types":["proc-macro"],"name":"repro","src_path":"/git/repro/src/lib.rs","edition":"2021","doc":true,"doctest":true,"test":true},"profile":{"opt_level":"0","debuginfo":2,"debug_assertions":true,"overflow_checks":true,"test":false},"features":[],"filenames":["/git/repro/target/debug/deps/librepro-c697fecae630a328.rmeta"],"executable":null,"fresh":false}
{"reason":"compiler-artifact","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["proc-macro"],"crate_types":["proc-macro"],"name":"repro","src_path":"/git/repro/src/lib.rs","edition":"2021","doc":true,"doctest":true,"test":true},"profile":{"opt_level":"0","debuginfo":2,"debug_assertions":true,"overflow_checks":true,"test":false},"features":[],"filenames":["/git/repro/target/debug/deps/librepro-433aa5011bfe20c0.so"],"executable":null,"fresh":false}
{"reason":"compiler-message","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"repro","src_path":"/git/repro/src/main.rs","edition":"2021","doc":true,"doctest":false,"test":true},"message":{"rendered":"error[E0277]: the size for values of type `str` cannot be known at compilation time\n --> src/main.rs:3:1\n  |\n3 | repro::repro!();\n  | ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time\n  |\n  = help: the trait `Sized` is not implemented for `str`\nnote: required by a bound in `f`\n --> src/main.rs:3:1\n  |\n3 | repro::repro!();\n  | ^^^^^^^^^^^^^^^ required by this bound in `f`\n  = note: this error originates in the macro `repro::repro` (in Nightly builds, run with -Z macro-backtrace for more info)\n\n","children":[{"children":[],"code":null,"level":"help","message":"the trait `Sized` is not implemented for `str`","rendered":null,"spans":[]},{"children":[],"code":null,"level":"note","message":"required by a bound in `f`","rendered":null,"spans":[{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":{"def_site_span":{"byte_end":167,"byte_start":119,"column_end":49,"column_start":1,"expansion":null,"file_name":"/git/repro/src/lib.rs","is_primary":false,"label":null,"line_end":6,"line_start":6,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":49,"highlight_start":1,"text":"pub fn repro(_input: TokenStream) -> TokenStream {"}]},"macro_decl_name":"repro::repro!","span":{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":null,"file_name":"src/main.rs","is_primary":false,"label":null,"line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}},"file_name":"src/main.rs","is_primary":true,"label":"required by this bound in `f`","line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}]}],"code":{"code":"E0277","explanation":"You tried to use a type which doesn't implement some trait in a place which\nexpected that trait.\n\nErroneous code example:\n\n```compile_fail,E0277\n// here we declare the Foo trait with a bar method\ntrait Foo {\n    fn bar(&self);\n}\n\n// we now declare a function which takes an object implementing the Foo trait\nfn some_func<T: Foo>(foo: T) {\n    foo.bar();\n}\n\nfn main() {\n    // we now call the method with the i32 type, which doesn't implement\n    // the Foo trait\n    some_func(5i32); // error: the trait bound `i32 : Foo` is not satisfied\n}\n```\n\nIn order to fix this error, verify that the type you're using does implement\nthe trait. Example:\n\n```\ntrait Foo {\n    fn bar(&self);\n}\n\n// we implement the trait on the i32 type\nimpl Foo for i32 {\n    fn bar(&self) {}\n}\n\nfn some_func<T: Foo>(foo: T) {\n    foo.bar(); // we can now use this method since i32 implements the\n               // Foo trait\n}\n\nfn main() {\n    some_func(5i32); // ok!\n}\n```\n\nOr in a generic context, an erroneous code example would look like:\n\n```compile_fail,E0277\nfn some_func<T>(foo: T) {\n    println!(\"{:?}\", foo); // error: the trait `core::fmt::Debug` is not\n                           //        implemented for the type `T`\n}\n\nfn main() {\n    // We now call the method with the i32 type,\n    // which *does* implement the Debug trait.\n    some_func(5i32);\n}\n```\n\nNote that the error here is in the definition of the generic function. Although\nwe only call it with a parameter that does implement `Debug`, the compiler\nstill rejects the function. It must work with all possible input types. In\norder to make this example compile, we need to restrict the generic type we're\naccepting:\n\n```\nuse std::fmt;\n\n// Restrict the input type to types that implement Debug.\nfn some_func<T: fmt::Debug>(foo: T) {\n    println!(\"{:?}\", foo);\n}\n\nfn main() {\n    // Calling the method is still fine, as i32 implements Debug.\n    some_func(5i32);\n\n    // This would fail to compile now:\n    // struct WithoutDebug;\n    // some_func(WithoutDebug);\n}\n```\n\nRust only looks at the signature of the called function, as such it must\nalready specify all requirements that will be used for every type parameter.\n"},"level":"error","message":"the size for values of type `str` cannot be known at compilation time","spans":[{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":{"def_site_span":{"byte_end":167,"byte_start":119,"column_end":49,"column_start":1,"expansion":null,"file_name":"/git/repro/src/lib.rs","is_primary":false,"label":null,"line_end":6,"line_start":6,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":49,"highlight_start":1,"text":"pub fn repro(_input: TokenStream) -> TokenStream {"}]},"macro_decl_name":"repro::repro!","span":{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":null,"file_name":"src/main.rs","is_primary":false,"label":null,"line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}},"file_name":"src/main.rs","is_primary":true,"label":"doesn't have a size known at compile-time","line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}]}}
{"reason":"compiler-message","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"repro","src_path":"/git/repro/src/main.rs","edition":"2021","doc":true,"doctest":false,"test":true},"message":{"rendered":"error[E0277]: the size for values of type `str` cannot be known at compilation time\n --> src/main.rs:3:1\n  |\n3 | repro::repro!();\n  | ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time\n  |\n  = help: the trait `Sized` is not implemented for `str`\nnote: required by a bound in `f`\n --> src/main.rs:3:1\n  |\n3 | repro::repro!();\n  | ^^^^^^^^^^^^^^^ required by this bound in `f`\n  = note: this error originates in the macro `repro::repro` (in Nightly builds, run with -Z macro-backtrace for more info)\n\n","children":[{"children":[],"code":null,"level":"help","message":"the trait `Sized` is not implemented for `str`","rendered":null,"spans":[]},{"children":[],"code":null,"level":"note","message":"required by a bound in `f`","rendered":null,"spans":[{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":{"def_site_span":{"byte_end":167,"byte_start":119,"column_end":49,"column_start":1,"expansion":null,"file_name":"/git/repro/src/lib.rs","is_primary":false,"label":null,"line_end":6,"line_start":6,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":49,"highlight_start":1,"text":"pub fn repro(_input: TokenStream) -> TokenStream {"}]},"macro_decl_name":"repro::repro!","span":{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":null,"file_name":"src/main.rs","is_primary":false,"label":null,"line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}},"file_name":"src/main.rs","is_primary":true,"label":"required by this bound in `f`","line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}]}],"code":{"code":"E0277","explanation":"You tried to use a type which doesn't implement some trait in a place which\nexpected that trait.\n\nErroneous code example:\n\n```compile_fail,E0277\n// here we declare the Foo trait with a bar method\ntrait Foo {\n    fn bar(&self);\n}\n\n// we now declare a function which takes an object implementing the Foo trait\nfn some_func<T: Foo>(foo: T) {\n    foo.bar();\n}\n\nfn main() {\n    // we now call the method with the i32 type, which doesn't implement\n    // the Foo trait\n    some_func(5i32); // error: the trait bound `i32 : Foo` is not satisfied\n}\n```\n\nIn order to fix this error, verify that the type you're using does implement\nthe trait. Example:\n\n```\ntrait Foo {\n    fn bar(&self);\n}\n\n// we implement the trait on the i32 type\nimpl Foo for i32 {\n    fn bar(&self) {}\n}\n\nfn some_func<T: Foo>(foo: T) {\n    foo.bar(); // we can now use this method since i32 implements the\n               // Foo trait\n}\n\nfn main() {\n    some_func(5i32); // ok!\n}\n```\n\nOr in a generic context, an erroneous code example would look like:\n\n```compile_fail,E0277\nfn some_func<T>(foo: T) {\n    println!(\"{:?}\", foo); // error: the trait `core::fmt::Debug` is not\n                           //        implemented for the type `T`\n}\n\nfn main() {\n    // We now call the method with the i32 type,\n    // which *does* implement the Debug trait.\n    some_func(5i32);\n}\n```\n\nNote that the error here is in the definition of the generic function. Although\nwe only call it with a parameter that does implement `Debug`, the compiler\nstill rejects the function. It must work with all possible input types. In\norder to make this example compile, we need to restrict the generic type we're\naccepting:\n\n```\nuse std::fmt;\n\n// Restrict the input type to types that implement Debug.\nfn some_func<T: fmt::Debug>(foo: T) {\n    println!(\"{:?}\", foo);\n}\n\nfn main() {\n    // Calling the method is still fine, as i32 implements Debug.\n    some_func(5i32);\n\n    // This would fail to compile now:\n    // struct WithoutDebug;\n    // some_func(WithoutDebug);\n}\n```\n\nRust only looks at the signature of the called function, as such it must\nalready specify all requirements that will be used for every type parameter.\n"},"level":"error","message":"the size for values of type `str` cannot be known at compilation time","spans":[{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":{"def_site_span":{"byte_end":167,"byte_start":119,"column_end":49,"column_start":1,"expansion":null,"file_name":"/git/repro/src/lib.rs","is_primary":false,"label":null,"line_end":6,"line_start":6,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":49,"highlight_start":1,"text":"pub fn repro(_input: TokenStream) -> TokenStream {"}]},"macro_decl_name":"repro::repro!","span":{"byte_end":31,"byte_start":16,"column_end":16,"column_start":1,"expansion":null,"file_name":"src/main.rs","is_primary":false,"label":null,"line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}},"file_name":"src/main.rs","is_primary":true,"label":"doesn't have a size known at compile-time","line_end":3,"line_start":3,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":16,"highlight_start":1,"text":"repro::repro!();"}]}]}}
{"reason":"compiler-message","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"repro","src_path":"/git/repro/src/main.rs","edition":"2021","doc":true,"doctest":false,"test":true},"message":{"rendered":"error: aborting due to 2 previous errors\n\n","children":[],"code":null,"level":"error","message":"aborting due to 2 previous errors","spans":[]}}
{"reason":"compiler-message","package_id":"repro 0.0.0 (path+file:///git/repro)","manifest_path":"/git/repro/Cargo.toml","target":{"kind":["bin"],"crate_types":["bin"],"name":"repro","src_path":"/git/repro/src/main.rs","edition":"2021","doc":true,"doctest":false,"test":true},"message":{"rendered":"For more information about this error, try `rustc --explain E0277`.\n","children":[],"code":null,"level":"failure-note","message":"For more information about this error, try `rustc --explain E0277`.","spans":[]}}
{"reason":"build-finished","success":false}
```

(host: x86_64-unknown-linux-gnu)

Notice that the first "compiler-message" (3rd JSON object) in the nightly-2023-01-02 output appears twice (3rd and 4th JSON object) in the nightly-2023-01-03 output. The duplicate lines are exactly identical.

If CARGO_INCREMENTAL=0 is set, the duplication does not occur.

The regression bisects to https://github.com/rust-lang/rust/pull/84762. @cjgillot @petrochenkov 

I am reporting this here instead of rust-lang/cargo because the description of that PR makes it sound like it was intended to be an internal refactor only with no user-facing consequence.