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@samueltardieu samueltardieu commented Aug 23, 2025

MIR validation attempts to determine the number of bytes needed to represent the size of the source type to compute the discriminant for the inhabited target enum. For a ZST source, there is no source data to use as a discriminant so no proper runtime check can be generated.

Since that should never be possible, insert a delayed bug to ensure the problem has been properly reported to the user by the type checker.

Fixes #145786

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rustbot commented Aug 23, 2025

r? @lcnr

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@rustbot 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 Aug 23, 2025
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rustbot commented Aug 23, 2025

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

MIR validation attempts to determine the number of bytes needed to
represent the size of the source type to compute the discriminant for
the inhabited target enum. For a ZST source, there is no source data to
use as a discriminant so no proper runtime check can be generated.

Since that should never be possible, insert a delayed bug to ensure the
problem has been properly reported to the user by the type checker.
@samueltardieu samueltardieu force-pushed the fix-zst-to-enum-mir-validation branch from 3b26db1 to 323e230 Compare August 23, 2025 17:26
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@bors r+ rollup

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bors commented Aug 23, 2025

📌 Commit 323e230 has been approved by compiler-errors

It is now in the queue for this repository.

@bors 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 Aug 23, 2025
bors added a commit that referenced this pull request Aug 23, 2025
Rollup of 14 pull requests

Successful merges:

 - #143898 (opt-dist: rebuild rustc when doing static LLVM builds)
 - #144452 (std/sys/fd: Relax `READ_LIMIT` on Darwin)
 - #145234 (match exhaustiveness diagnostics: show a trailing comma on singleton tuple consructors in witness patterns (and clean up a little))
 - #145515 (Optimize `char::encode_utf8`)
 - #145540 (interpret/allocation: get_range on ProvenanceMap)
 - #145670 (port `sanitize` attribute to the new parsing infrastructure)
 - #145713 (next-solver: fix `feature(const_trait_impl)` bootstrap)
 - #145729 (Remove two duplicated crates)
 - #145744 (miri: also detect aliasing of in-place argument and return place)
 - #145774 (Remove default opts from config)
 - #145781 (Remove profile section from Clippy)
 - #145782 (rustdoc: make attributes render consistently)
 - #145787 (citool: cleanup `mismatched_lifetime_syntaxes` warnings)
 - #145791 (Fix ICE when validating transmuting ZST to inhabited enum)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 4d38062 into rust-lang:master Aug 24, 2025
10 checks passed
rust-timer added a commit that referenced this pull request Aug 24, 2025
Rollup merge of #145791 - samueltardieu:fix-zst-to-enum-mir-validation, r=compiler-errors

Fix ICE when validating transmuting ZST to inhabited enum

MIR validation attempts to determine the number of bytes needed to represent the size of the source type to compute the discriminant for the inhabited target enum. For a ZST source, there is no source data to use as a discriminant so no proper runtime check can be generated.

Since that should never be possible, insert a delayed bug to ensure the problem has been properly reported to the user by the type checker.

Fixes #145786
@rustbot rustbot added this to the 1.91.0 milestone Aug 24, 2025
github-actions bot pushed a commit to rust-lang/miri that referenced this pull request Aug 24, 2025
Rollup of 14 pull requests

Successful merges:

 - rust-lang/rust#143898 (opt-dist: rebuild rustc when doing static LLVM builds)
 - rust-lang/rust#144452 (std/sys/fd: Relax `READ_LIMIT` on Darwin)
 - rust-lang/rust#145234 (match exhaustiveness diagnostics: show a trailing comma on singleton tuple consructors in witness patterns (and clean up a little))
 - rust-lang/rust#145515 (Optimize `char::encode_utf8`)
 - rust-lang/rust#145540 (interpret/allocation: get_range on ProvenanceMap)
 - rust-lang/rust#145670 (port `sanitize` attribute to the new parsing infrastructure)
 - rust-lang/rust#145713 (next-solver: fix `feature(const_trait_impl)` bootstrap)
 - rust-lang/rust#145729 (Remove two duplicated crates)
 - rust-lang/rust#145744 (miri: also detect aliasing of in-place argument and return place)
 - rust-lang/rust#145774 (Remove default opts from config)
 - rust-lang/rust#145781 (Remove profile section from Clippy)
 - rust-lang/rust#145782 (rustdoc: make attributes render consistently)
 - rust-lang/rust#145787 (citool: cleanup `mismatched_lifetime_syntaxes` warnings)
 - rust-lang/rust#145791 (Fix ICE when validating transmuting ZST to inhabited enum)

r? `@ghost`
`@rustbot` modify labels: rollup
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ICE: Found discriminant with invalid size, has 0 bytes
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