Experimentally add heterogeneous `try` blocks #149489

scottmcm · 2025-11-30T22:49:38Z

#148725 moved the default to being homogeneous; this adds heterogeneous ones back under an obvious-bikeshed syntax so people can experiment with that as well.

Essentially resolves #149025 by letting them move to this syntax instead.

New tracking issue: #149488
Related RFC: rust-lang/rfcs#3721 (comment) (specifically about experimenting)

rustbot · 2025-11-30T22:49:44Z

r? @nnethercote

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rustbot · 2025-11-30T23:09:49Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2025-11-30T23:36:00Z

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

nnethercote · 2025-12-09T06:59:20Z

compiler/rustc_ast_lowering/src/lib.rs


+#[derive(Copy, Clone, Debug)]
+enum TryBlockScope {
+    /// There isn't a `try` block, so the scope is the function or closure or ...


It took me a few reads to understand this comment. Can it be rephrased? What other possibilities are there?

nnethercote · 2025-12-09T07:03:34Z

compiler/rustc_ast/src/ast.rs

-    /// A try block (`try { ... }`).
-    TryBlock(Box<Block>),
+    /// A try block (`try { ... }`), if the type is `None`, or
+    /// A try block (`try bikeshed Ty { ... }`) if the type is `Some`.


Nowhere in the PR is an explanation that bikeshed is deliberately ridiculous placeholder syntax. (I assume that's what it is.) Probably worth mentioning at least once. This might be a good spot for it.

nnethercote · 2025-12-09T07:04:39Z

Standard plumbing, mostly, seems fine.

r=me with the nits addressed.

148725 moved the default to being homogeneous; this adds heterogeneous ones back under an obvious-bikeshed syntax so people can experiment with that as well. Essentially resolves 149025 by letting them move to this syntax instead.

rustbot · 2025-12-10T04:18:56Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2025-12-10T05:46:01Z

@bors r=nnethercote

bors · 2025-12-10T05:46:04Z

📌 Commit 35598c1 has been approved by nnethercote

It is now in the queue for this repository.

nxsaken · 2025-12-10T12:46:13Z

compiler/rustc_ast_lowering/src/lib.rs

+    /// We're inside a `try { … }` block, so a `?` will block-break
+    /// from that block using a type depending only on the argument.
+    Homogeneous(HirId),
+    /// We're inside a `try as _ { … }` block, so a `?` will block-break


Suggested change

/// We're inside a `try as _ { … }` block, so a `?` will block-break

/// We're inside a `try bikeshed _ { … }` block, so a `?` will block-break

nxsaken · 2025-12-10T12:50:37Z

compiler/rustc_ast/src/visit.rs

+                ExprKind::TryBlock(body, optional_type) =>
+                    visit_visitable!($($mut)? vis, body, optional_type),


Suggested change

ExprKind::TryBlock(body, optional_type) =>

visit_visitable!($($mut)? vis, body, optional_type),

ExprKind::TryBlock(body, opt_ty) =>

visit_visitable!($($mut)? vis, body, opt_ty),

(For simpler searching, since other places use opt_ty.)

Rollup of 7 pull requests Successful merges: - #148052 (Stabilize `const_mul_add`) - #149386 (Display funding link in the github overview) - #149489 (Experimentally add *heterogeneous* `try` blocks) - #149764 (Make `--print=backend-has-zstd` work by default on any backend) - #149838 (Build auxiliary in pretty tests) - #149839 (Use `PointeeSized` bound for `TrivialClone` impls) - #149846 (Statically require links to an issue or the edition guide for all FCWs) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #149489 - scottmcm:try-bikeshed, r=nnethercote Experimentally add *heterogeneous* `try` blocks #148725 moved the default to being homogeneous; this adds heterogeneous ones back under an obvious-bikeshed syntax so people can experiment with that as well. Essentially resolves #149025 by letting them move to this syntax instead. New tracking issue: #149488 Related RFC: rust-lang/rfcs#3721 (comment) (specifically about experimenting)

Experimentally add *heterogeneous* `try` blocks rust-lang#148725 moved the default to being homogeneous; this adds heterogeneous ones back under an obvious-bikeshed syntax so people can experiment with that as well. Essentially resolves rust-lang#149025 by letting them move to this syntax instead. New tracking issue: rust-lang#149488 Related RFC: rust-lang/rfcs#3721 (comment) (specifically about experimenting)

rustbot assigned nnethercote Nov 30, 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 Nov 30, 2025

This was referenced Nov 30, 2025

Possible try blocks regression in nightly #149025

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Experimental Tracking Issue for Heterogeneous Try Blocks #149488

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rustbot added the T-clippy Relevant to the Clippy team. label Nov 30, 2025

scottmcm mentioned this pull request Nov 30, 2025

Add homogeneous_try_blocks RFC rust-lang/rfcs#3721

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rustbot added the T-rustfmt Relevant to the rustfmt team, which will review and decide on the PR/issue. label Nov 30, 2025

nnethercote approved these changes Dec 9, 2025

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nnethercote 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 Dec 9, 2025

scottmcm added 3 commits December 9, 2025 20:18

Experimentally add *heterogeneous* try blocks

4033d19

148725 moved the default to being homogeneous; this adds heterogeneous ones back under an obvious-bikeshed syntax so people can experiment with that as well. Essentially resolves 149025 by letting them move to this syntax instead.

Update clippy for the ast TryBlock change

f9e1031

Also get rustfmt to at least compile

35598c1

scottmcm force-pushed the try-bikeshed branch from 348490d to 35598c1 Compare December 10, 2025 04:18

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 10, 2025

nxsaken reviewed Dec 10, 2025

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matthiaskrgr mentioned this pull request Dec 10, 2025

Rollup of 7 pull requests #149853

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bors merged commit 02a58a9 into rust-lang:main Dec 10, 2025
11 checks passed

rustbot added this to the 1.94.0 milestone Dec 10, 2025

github-actions bot mentioned this pull request Dec 12, 2025

Toolchain upgrade to nightly-2025-12-11 flux-rs/flux#1345

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rust-timer mentioned this pull request Dec 12, 2025

Rollup of 7 pull requests #149909

Merged

	/// We're inside a `try as _ { … }` block, so a `?` will block-break
	/// We're inside a `try bikeshed _ { … }` block, so a `?` will block-break

		ExprKind::TryBlock(body, optional_type) =>
		visit_visitable!($($mut)? vis, body, optional_type),

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Experimentally add *heterogeneous* try blocks #149489

Experimentally add *heterogeneous* try blocks #149489

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Experimentally add heterogeneous `try` blocks #149489

Experimentally add heterogeneous `try` blocks #149489

scottmcm commented Nov 30, 2025 •

edited by rustbot

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