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Auto merge of #90473 - joshtriplett:stabilize-format-args-capture, r=Mark-Simulacrum

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stabilize format args capture

Works as expected, and there are widespread reports of success with it, as well as interest in it.

RFC: rust-lang/rfcs#2795
Tracking issue: https://github.com/rust-lang/rust/issues/67984

Addressing items from the tracking issue:

- We don't support capturing arguments from a non-literal format string like `format_args!(concat!(...))`. We could add that in a future enhancement, or we can decide that it isn't supported (as suggested in https://github.com/rust-lang/rust/issues/67984#issuecomment-801394736 ).
- I've updated the documentation.
- `panic!` now supports capture as well.
- There are potentially opportunities to further improve diagnostics for invalid usage, such as if it looks like the user tried to use an expression rather than a variable. However, such cases are all already caught and provide reasonable syntax errors now, and we can always provided even friendlier diagnostics in the future.
This commit is contained in:
bors 2021-11-15 16:10:19 +00:00
commit c26746af5a
22 changed files with 83 additions and 167 deletions
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2
compiler/rustc_borrowck/src/lib.rs
View file

@ -3,7 +3,7 @@
#![feature(bool_to_option)]
#![feature(box_patterns)]
#![feature(crate_visibility_modifier)]
#![feature(format_args_capture)]
#![cfg_attr(bootstrap, feature(format_args_capture))]
#![feature(in_band_lifetimes)]
#![feature(iter_zip)]
#![feature(let_else)]

36
compiler/rustc_builtin_macros/src/format.rs
View file

@ -527,17 +527,9 @@ impl<'a, 'b> Context<'a, 'b> {
self.verify_arg_type(Exact(idx), ty)
}
None => {
let capture_feature_enabled = self
.ecx
.ecfg
.features
.map_or(false, |features| features.format_args_capture);
// For the moment capturing variables from format strings expanded from macros is
// disabled (see RFC #2795)
let can_capture = capture_feature_enabled && self.is_literal;
if can_capture {
if self.is_literal {
// Treat this name as a variable to capture from the surrounding scope
let idx = self.args.len();
self.arg_types.push(Vec::new());
@ -559,23 +551,15 @@ impl<'a, 'b> Context<'a, 'b> {
};
let mut err = self.ecx.struct_span_err(sp, &msg[..]);
if capture_feature_enabled && !self.is_literal {
err.note(&format!(
"did you intend to capture a variable `{}` from \
the surrounding scope?",
name
));
err.note(
"to avoid ambiguity, `format_args!` cannot capture variables \
when the format string is expanded from a macro",
);
} else if self.ecx.parse_sess().unstable_features.is_nightly_build() {
err.help(&format!(
"if you intended to capture `{}` from the surrounding scope, add \
`#![feature(format_args_capture)]` to the crate attributes",
name
));
}
err.note(&format!(
"did you intend to capture a variable `{}` from \
the surrounding scope?",
name
));
err.note(
"to avoid ambiguity, `format_args!` cannot capture variables \
when the format string is expanded from a macro",
);
err.emit();
}

2
compiler/rustc_errors/src/lib.rs
View file

@ -6,7 +6,7 @@
#![feature(crate_visibility_modifier)]
#![feature(backtrace)]
#![feature(if_let_guard)]
#![feature(format_args_capture)]
#![cfg_attr(bootstrap, feature(format_args_capture))]
#![feature(iter_zip)]
#![feature(let_else)]
#![feature(nll)]

2
compiler/rustc_expand/src/lib.rs
View file

@ -1,7 +1,7 @@
#![feature(crate_visibility_modifier)]
#![feature(decl_macro)]
#![feature(destructuring_assignment)]
#![feature(format_args_capture)]
#![cfg_attr(bootstrap, feature(format_args_capture))]
#![feature(if_let_guard)]
#![feature(iter_zip)]
#![feature(let_else)]

2
compiler/rustc_feature/src/accepted.rs
View file

@ -301,6 +301,8 @@ declare_features! (
(accepted, relaxed_struct_unsize, "1.58.0", Some(81793), None),
/// Allows dereferencing raw pointers during const eval.
(accepted, const_raw_ptr_deref, "1.58.0", Some(51911), None),
/// Allows capturing variables in scope using format_args!
(accepted, format_args_capture, "1.58.0", Some(67984), None),
// -------------------------------------------------------------------------
// feature-group-end: accepted features

3
compiler/rustc_feature/src/active.rs
View file

@ -539,9 +539,6 @@ declare_features! (
/// Be more precise when looking for live drops in a const context.
(active, const_precise_live_drops, "1.46.0", Some(73255), None),
/// Allows capturing variables in scope using format_args!
(active, format_args_capture, "1.46.0", Some(67984), None),
/// Allows `if let` guard in match arms.
(active, if_let_guard, "1.47.0", Some(51114), None),

2
compiler/rustc_lint/src/lib.rs
View file

@ -30,7 +30,7 @@
#![feature(bool_to_option)]
#![feature(box_patterns)]
#![feature(crate_visibility_modifier)]
#![feature(format_args_capture)]
#![cfg_attr(bootstrap, feature(format_args_capture))]
#![feature(iter_order_by)]
#![feature(iter_zip)]
#![feature(never_type)]

2
compiler/rustc_passes/src/lib.rs
View file

@ -7,7 +7,7 @@
#![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
#![feature(crate_visibility_modifier)]
#![feature(in_band_lifetimes)]
#![feature(format_args_capture)]
#![cfg_attr(bootstrap, feature(format_args_capture))]
#![feature(iter_zip)]
#![feature(map_try_insert)]
#![feature(min_specialization)]

2
compiler/rustc_resolve/src/lib.rs
View file

@ -13,7 +13,7 @@
#![feature(drain_filter)]
#![feature(bool_to_option)]
#![feature(crate_visibility_modifier)]
#![feature(format_args_capture)]
#![cfg_attr(bootstrap, feature(format_args_capture))]
#![feature(iter_zip)]
#![feature(let_else)]
#![feature(never_type)]

2
compiler/rustc_typeck/src/lib.rs
View file

@ -58,7 +58,7 @@ This API is completely unstable and subject to change.
#![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
#![feature(bool_to_option)]
#![feature(crate_visibility_modifier)]
#![feature(format_args_capture)]
#![cfg_attr(bootstrap, feature(format_args_capture))]
#![feature(if_let_guard)]
#![feature(in_band_lifetimes)]
#![feature(is_sorted)]