[experiment] first draft of init array syntax #143553

dingxiangfei2009 · 2025-07-07T00:03:06Z

This patch allows parsing of the syntax init [ v1, v2, v3, .. ] and certain level of type checking on HIR level.

See Draft RFC, under tracking rust-lang/lang-team#336

Dragons ahead

This is a draft PR that is very experimental and it is posted only for very early feedback and it is not immediately mergeable.

This patch introduces changes to the parser to accept init # ... AST fragment as a start.
The reason that this deviates from the original proposal, with the additional #, is to help with syntax ambiguity between init[0] as indexing into a value init, versus init [ 0 ] as in-place initialisation.
However, I would propose to switch to a macro based approach to the syntax to avoid such ambiguity.
This patch introduces a new type category Init. It has the same generics structure as a Closure and it is almost type-checked in the same way as Closure, except that its return type expectation also contains the error type, which is to be unified with those from the nested in-place initialisation.
This is still not functional, because for instance I still have to fill out some tables such as late_bound_vars.

This patch does not include any THIR or MIR building.

The final state at which I would see this patch can be merged, is to at least we can type check the following smoke test.

#![feature(in_place_initialization)]
use std::init::Init;

fn smoke() -> impl Init<[i32; 1]> {
    init # [0]
}

fn main() {}

Areas to improve

As of July 7th, I see that I need to work these out

The AST node InitTail is not necessary, I should just drop it
~~The HIR node InitKind::Array could be squashed so that it is just a list of InitTail nodes~~ I start to appreciate this choice now because the HIR visitor would be a bit harder to write if I would decide to squash it.
The HIR node names. I don't find them descriptive. InitTail sounds terrible and I regret the choice.

r? @compiler-errors

bors · 2025-07-07T18:30:58Z

☔ The latest upstream changes (presumably #143582) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2025-07-09T23:41:22Z

☔ The latest upstream changes (presumably #143538) made this pull request unmergeable. Please resolve the merge conflicts.

This patch allows parsing of the syntax `init [ v1, v2, v3, .. ]` and certain level of type checking on HIR level. Signed-off-by: Xiangfei Ding <[email protected]>

rust-log-analyzer · 2025-07-23T21:21:22Z

The job aarch64-gnu-llvm-19-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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


---- [debuginfo-gdb] tests/debuginfo/function-names.rs stdout ----
NOTE: compiletest thinks it is using GDB version 15001000

error: check directive(s) from `/checkout/tests/debuginfo/function-names.rs` not found in debugger output. errors:
    (function-names.rs:40) `[...]static fn function_names::const_generic_fn_non_int<{CONST#ffa3db4ca1d52dce}>();`
the following subset of check directive(s) was found successfully:
    (function-names.rs:10) `90: static fn function_names::main();`
    (function-names.rs:12) `192: static fn function_names::generic_func<i32>(i32) -> i32;`
    (function-names.rs:16) `160: static fn function_names::GenericStruct<i32, i32>::impl_function<i32, i32>();`
    (function-names.rs:17) `148: static fn function_names::Mod1::TestStruct2::impl_function();`
    (function-names.rs:18) `132: static fn function_names::TestStruct1::impl_function();`
    (function-names.rs:22) `152: static fn function_names::Mod1::{impl#1}::trait_function();`
    (function-names.rs:23) `137: static fn function_names::{impl#1}::trait_function();`
    (function-names.rs:24) `169: static fn function_names::{impl#3}::trait_function<i32>();`
    (function-names.rs:25) `183: static fn function_names::{impl#5}::trait_function3<function_names::TestStruct1>();`
    (function-names.rs:26) `188: static fn function_names::{impl#6}::trait_function<i32, 1>();`
    (function-names.rs:30) `194: static fn function_names::generic_func::{closure#0}<i32>(*mut function_names::generic_func::{closure_env#0}<i32>);`
    (function-names.rs:31) `107: static fn function_names::main::{closure#0}(*mut function_names::main::{closure_env#0});`
    (function-names.rs:32) `162: static fn function_names::{impl#2}::impl_function::{closure#0}<i32, i32>(*mut function_names::{impl#2}::impl_function::{closure_env#0}<i32, i32>);`
    (function-names.rs:39) `200: static fn function_names::const_generic_fn_bool<false>();`
    (function-names.rs:41) `202: static fn function_names::const_generic_fn_signed_int<-7>();`
    (function-names.rs:42) `203: static fn function_names::const_generic_fn_unsigned_int<14>();`
status: exit status: 0
command: PYTHONPATH="/checkout/src/etc" "/usr/bin/gdb" "-quiet" "-batch" "-nx" "-command=/checkout/obj/build/aarch64-unknown-linux-gnu/test/debuginfo/function-names.gdb/function-names.debugger.script"
--- stdout -------------------------------
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
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Type "show configuration" for configuration details.
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File /checkout/tests/debuginfo/function-names.rs:
90: static fn function_names::main();
107: static fn function_names::main::{closure#0}(*mut function_names::main::{closure_env#0});
112: static fn function_names::main::{coroutine#1}(core::pin::Pin<&mut function_names::main::{coroutine_env#1}>, ()) -> core::ops::coroutine::CoroutineState<(), ()>;

File /rustc/FAKE_PREFIX/library/core/src/ptr/mod.rs:
804: static fn core::ptr::drop_in_place<function_names::main::{coroutine_env#1}>(*mut function_names::main::{coroutine_env#1});

File /checkout/tests/debuginfo/function-names.rs:
194: static fn function_names::generic_func::{closure#0}<i32>(*mut function_names::generic_func::{closure_env#0}<i32>);
192: static fn function_names::generic_func<i32>(i32) -> i32;

File /checkout/tests/debuginfo/function-names.rs:
160: static fn function_names::GenericStruct<i32, i32>::impl_function<i32, i32>();
148: static fn function_names::Mod1::TestStruct2::impl_function();
132: static fn function_names::TestStruct1::impl_function();
162: static fn function_names::{impl#2}::impl_function::{closure#0}<i32, i32>(*mut function_names::{impl#2}::impl_function::{closure_env#0}<i32, i32>);

File /checkout/tests/debuginfo/function-names.rs:
152: static fn function_names::Mod1::{impl#1}::trait_function();
137: static fn function_names::{impl#1}::trait_function();
169: static fn function_names::{impl#3}::trait_function<i32>();
183: static fn function_names::{impl#5}::trait_function3<function_names::TestStruct1>();
188: static fn function_names::{impl#6}::trait_function<i32, 1>();

File /checkout/tests/debuginfo/function-names.rs:
194: static fn function_names::generic_func::{closure#0}<i32>(*mut function_names::generic_func::{closure_env#0}<i32>);
107: static fn function_names::main::{closure#0}(*mut function_names::main::{closure_env#0});
162: static fn function_names::{impl#2}::impl_function::{closure#0}<i32, i32>(*mut function_names::{impl#2}::impl_function::{closure_env#0}<i32, i32>);

File /checkout/tests/debuginfo/function-names.rs:
200: static fn function_names::const_generic_fn_bool<false>();
201: static fn function_names::const_generic_fn_non_int<{CONST#5177fe61e1757625}>();
202: static fn function_names::const_generic_fn_signed_int<-7>();
203: static fn function_names::const_generic_fn_unsigned_int<14>();
------------------------------------------
stderr: none

bors · 2025-07-25T14:56:05Z

☔ The latest upstream changes (presumably #144440) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot assigned compiler-errors Jul 7, 2025

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bors added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jul 7, 2025

dingxiangfei2009 force-pushed the init-array branch from 8c3dff6 to 04fd5fd Compare July 9, 2025 14:21

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dingxiangfei2009 force-pushed the init-array branch from 04fd5fd to c6a4400 Compare July 14, 2025 22:23

rustbot added the T-clippy Relevant to the Clippy team. label Jul 14, 2025

dingxiangfei2009 added 2 commits July 23, 2025 18:29

first draft of init array syntax

4f03c5d

This patch allows parsing of the syntax `init [ v1, v2, v3, .. ]` and certain level of type checking on HIR level. Signed-off-by: Xiangfei Ding <[email protected]>

init drop guard and array-unsizing init

2007f50

dingxiangfei2009 force-pushed the init-array branch from c6a4400 to 2007f50 Compare July 23, 2025 20:37

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[experiment] first draft of init array syntax #143553

[experiment] first draft of init array syntax #143553

dingxiangfei2009 commented Jul 7, 2025 •

edited

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dingxiangfei2009 commented Jul 7, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Dragons ahead

Areas to improve

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dingxiangfei2009 commented Jul 7, 2025 •

edited

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