Add DesugaringKind::FormatLiteral #142594

mejrs · 2025-06-16T19:31:55Z

Implements DesugaringKind::FormatLiteral to mark the FormatArgs desugaring of format literals. The main use for this is to stop yapping about about formatting parameters if we're not anywhere near a format literal. The other use case is to fix suggestions such as #141350. It might also be useful for new or existing diagnostics that check whether they're in a format-like macro.

cc @xizheyin @fmease

rustbot · 2025-06-16T19:31:59Z

r? @SparrowLii

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rustbot · 2025-06-16T19:32:01Z

Some changes occurred in compiler/rustc_ast_lowering/src/format.rs

cc @m-ou-se

fmease · 2025-06-16T19:33:43Z

We might want to block this on #140748, I'm relatively sure. Just FYI

mejrs · 2025-06-16T19:43:45Z

Why is that?

fmease · 2025-06-16T19:53:59Z

Idk, if it's not conflicting according to git and if it's not stepping on each other's toes in other ways, I guess it's fine — I only skimmed boths diffs. Mara's PR will likely get approved soon anyway.

xizheyin

Great, #141633 can be refactored after this.

compiler/rustc_span/src/hygiene.rs

compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs

compiler/rustc_ast/src/format.rs

SparrowLii

This is very meaningful and the impl looks fine. But adding a new desugaringKind for diagnostics needs some opinions IMO
r? diagnostics

chenyukang · 2025-06-20T00:32:09Z

tests/ui/on-unimplemented/no-debug.stderr

@@ -17,7 +19,9 @@ error[E0277]: `Bar` doesn't implement `Debug`
  --> $DIR/no-debug.rs:10:32
   |
 LL |     println!("{:?} {:?}", Foo, Bar);
-   |                                ^^^ `Bar` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |                    ----        ^^^ `Bar` cannot be formatted using `{:?}` because it doesn't implement `Debug`


This change on diagnostic reminds me of this issue:
#140578

while we had a PR for it, but seems it's stalled.

Will this PR also resolve #140578? If so, we can link with it, add a unit test, and close that one too.

It doesn't, but it does make that PR easier to implement; they can simply replace all of the diagnostic item stuff with a matches!(span.desugaring_kind(), Some(rustc_span::DesugaringKind::FormatLiteral {..}))

tests/ui/rfcs/rfc-2361-dbg-macro/dbg-macro-requires-debug.stderr

chenyukang · 2025-06-20T00:35:46Z

tests/ui/suggestions/derive-macro-missing-bounds.stderr

@@ -4,9 +4,8 @@ error[E0277]: `a::Inner<T>` doesn't implement `Debug`
 LL |     #[derive(Debug)]
   |              ----- in this derive macro expansion
 LL |     struct Outer<T>(Inner<T>);
-   |                     ^^^^^^^^ `a::Inner<T>` cannot be formatted using `{:?}`
+   |                     ^^^^^^^^ the trait `Debug` is not implemented for `a::Inner<T>`


I'm neutral about this change. Maybe some beginners need to know the relationship between Debug and {:?}. I am not sure about this.

chenyukang · 2025-06-20T00:41:46Z

Looks ok for me.

@bors delegate+

bors · 2025-06-20T00:41:49Z

✌️ @mejrs, you can now approve this pull request!

If @chenyukang told you to "r=me" after making some further change, please make that change, then do @bors r=@chenyukang

mejrs · 2025-06-21T22:21:30Z

@bors r=@chenyukang

bors · 2025-06-21T22:21:33Z

📌 Commit 3858b2c has been approved by chenyukang

It is now in the queue for this repository.

Add DesugaringKind::FormatLiteral Implements `DesugaringKind::FormatLiteral` to mark the FormatArgs desugaring of format literals. The main use for this is to stop yapping about about formatting parameters if we're not anywhere near a format literal. The other use case is to fix suggestions such as rust-lang#141350. It might also be useful for new or existing diagnostics that check whether they're in a format-like macro. cc `@xizheyin` `@fmease`

Rollup of 10 pull requests Successful merges: - #140254 (Pass -Cpanic=abort for the panic_abort crate) - #142594 (Add DesugaringKind::FormatLiteral) - #142600 (Port `#[rustc_pub_transparent]` to the new attribute system) - #142617 (improve search graph docs, reset `encountered_overflow` between reruns) - #142641 (Generate symbols.o for proc-macros too) - #142747 (rustdoc_json: conversion cleanups) - #142776 (All HIR attributes are outer) - #142800 (integer docs: remove extraneous text) - #142850 (remove asm_goto feature annotation, for it is now stabilized) - #142860 (Notify me on tidy changes) r? `@ghost` `@rustbot` modify labels: rollup

jhpratt · 2025-06-22T02:24:05Z

@bors r-

#142861 (comment)

rustbot assigned SparrowLii Jun 16, 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. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jun 16, 2025

xizheyin reviewed Jun 17, 2025

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m-ou-se reviewed Jun 17, 2025

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Implement DesugaringKind::FormatLiteral

fe3b238

mejrs force-pushed the new_desugaring branch from c832fd8 to 0cd0b91 Compare June 17, 2025 14:02

Stop dbg! macro yapping about format modifiers

3858b2c

mejrs force-pushed the new_desugaring branch from 0cd0b91 to 3858b2c Compare June 17, 2025 17:37

SparrowLii reviewed Jun 18, 2025

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rustbot assigned chenyukang and unassigned SparrowLii Jun 18, 2025

chenyukang reviewed Jun 20, 2025

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chenyukang reviewed Jun 20, 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 Jun 21, 2025

mejrs mentioned this pull request Jun 21, 2025

Fix unuseful span in type error in some format_args!() invocations #140916

Open

jhpratt mentioned this pull request Jun 22, 2025

Rollup of 10 pull requests #142861

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bors 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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jun 22, 2025

Add DesugaringKind::FormatLiteral #142594

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Add DesugaringKind::FormatLiteral #142594

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