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Auto merge of #103877 - oli-obk:const_eval_step_limit, r=fee1-dead

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Replace const eval limit by a lint and add an exponential backoff warning

The lint triggers at the first power of 2 that comes after 1 million function calls or traversed back-edges (takes less than a second on usual programs). After the first emission, an unsilenceable warning is repeated at every following power of 2 terminators, causing it to get reported less and less the longer the evaluation runs.

cc `@rust-lang/wg-const-eval`

fixes #93481
closes #67217
This commit is contained in:
bors 2023-06-01 05:32:00 +00:00
commit 23f93a1266
41 changed files with 325 additions and 261 deletions
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2
compiler/rustc_feature/src/active.rs
View file

@ -351,8 +351,6 @@ declare_features! (
(active, const_async_blocks, "1.53.0", Some(85368), None),
/// Allows `const || {}` closures in const contexts.
(incomplete, const_closures, "1.68.0", Some(106003), None),
/// Allows limiting the evaluation steps of const expressions
(active, const_eval_limit, "1.43.0", Some(67217), None),
/// Allows the definition of `const extern fn` and `const unsafe extern fn`.
(active, const_extern_fn, "1.40.0", Some(64926), None),
/// Allows basic arithmetic on floating point types in a `const fn`.

4
compiler/rustc_feature/src/builtin_attrs.rs
View file

@ -355,10 +355,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
// Limits:
ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
gated!(
const_eval_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
const_eval_limit, experimental!(const_eval_limit)
),
gated!(
move_size_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
large_assignments, experimental!(move_size_limit)

4
compiler/rustc_feature/src/removed.rs
View file

@ -59,8 +59,10 @@ declare_features! (
/// Allows comparing raw pointers during const eval.
(removed, const_compare_raw_pointers, "1.46.0", Some(53020), None,
Some("cannot be allowed in const eval in any meaningful way")),
/// Allows limiting the evaluation steps of const expressions
(removed, const_eval_limit, "1.43.0", Some(67217), None, Some("removed the limit entirely")),
/// Allows non-trivial generic constants which have to be manually propagated upwards.
(removed, const_evaluatable_checked, "1.48.0", Some(76560), None, Some("renamed to `generic_const_exprs`")),
(removed, const_evaluatable_checked, "1.48.0", Some(76560), None, Some("renamed to `generic_const_exprs`")),
/// Allows the definition of `const` functions with some advanced features.
(removed, const_fn, "1.54.0", Some(57563), None,
Some("split into finer-grained feature gates")),