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Using while in const fn results in a misleading error message on stable #61508

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not-an-aardvark opened this issue Jun 4, 2019 · 0 comments · Fixed by #61518
Closed

Using while in const fn results in a misleading error message on stable #61508

not-an-aardvark opened this issue Jun 4, 2019 · 0 comments · Fixed by #61518
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A-const-eval Area: Constant evaluation, covers all const contexts (static, const fn, ...) A-diagnostics Area: Messages for errors, warnings, and lints E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue.

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@not-an-aardvark
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When while is used in a const fn on stable, it produces an error message: `if`, `match`, `&&` and `||` are not stable in const fn. This is a bit confusing because the function does not explicitly contain if, match, &&, or ||.

I would expect the error message to also mention that while is disallowed, or say that "loops are not allowed in const fn" (which it does when loop {} construct is encountered).

(It seems like it would be even better to have a specific error message for the disallowed construct that the compiler encounters rather than just providing a list of disallowed constructs, if this is possible architecturally.)

rustc version 
rustc 1.35.0 (3c235d560 2019-05-20)
binary: rustc
commit-hash: 3c235d5600393dfe6c36eeed34042efad8d4f26e
commit-date: 2019-05-20
host: x86_64-apple-darwin
release: 1.35.0
LLVM version: 8.0
@estebank estebank added A-const-fn A-diagnostics Area: Messages for errors, warnings, and lints E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. labels Jun 4, 2019
@czipperz czipperz mentioned this issue Jun 4, 2019
Merged
Centril added a commit to Centril/rust that referenced this issue Jun 11, 2019
@Centril
Rollup merge of rust-lang#61518 - czipperz:const-fn-doc-disallow-loop…
17393b2 
…s, r=Centril

Add loops to doc list of things not stable in const fn

Closes rust-lang#61508
@RalfJung RalfJung added the A-const-eval Area: Constant evaluation, covers all const contexts (static, const fn, ...) label Dec 1, 2024
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A-const-eval Area: Constant evaluation, covers all const contexts (static, const fn, ...) A-diagnostics Area: Messages for errors, warnings, and lints E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue.
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Add loops to doc list of things not stable in const fn czipperz/rust
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@RalfJung @estebank @not-an-aardvark