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Document that -C opt-level=0 implies -C debug-assertions more prominently #39449

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mystor opened this issue Feb 1, 2017 · 3 comments
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Document that -C opt-level=0 implies -C debug-assertions more prominently #39449

mystor opened this issue Feb 1, 2017 · 3 comments

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@mystor
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mystor commented Feb 1, 2017

All I was able to find documenting this is an ambiguous mention in the rust reference:
https://github.com/rust-lang/rust/blob/17cae033787aca26b00a8c820c1599926a1fd94d/src/doc/reference.md#conditional-compilation

It would be nice if, for example, the documentation for std::debug_assert! was updated to mention:

Unlike assert!, debug_assert! statements are only enabled in non optimized builds by default. An optimized build will omit all debug_assert! statements unless -C debug-assertions or -C opt-level=0 is passed to the compiler. This makes debug_assert! useful for checks that are too expensive to be present in a release build but may be helpful during development.
@nagisa
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nagisa commented Feb 1, 2017

“An optimized build” seems to very clearly imply that opt-level ≠ 0 to me.

@mystor
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mystor commented Feb 1, 2017

That's true - I missed that on the first reading.

@mystor mystor closed this as completed Feb 1, 2017
@daxpedda
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Was currently trying to work with the cargo api and was struggling to find the issue until I found out about this.

In the new documentation this is mentioned nowhere:
https://doc.rust-lang.org/nightly/rustc/codegen-options/index.html#opt-level

@daxpedda daxpedda mentioned this issue Dec 26, 2018
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Centril added a commit to Centril/rust that referenced this issue Jan 18, 2019
@Centril
Rollup merge of rust-lang#57132 - daxpedda:master, r=steveklabnik
04a2cbd 
Document that `-C opt-level=0` implies `-C debug-assertions`.

I couldn't find it stated anywhere else (https://doc.rust-lang.org/nightly/rustc/codegen-options/index.html#opt-level).
It was a problem before here: rust-lang#39449, it got lost in the migration to the new documentation I assume.

On a sidenote: I think that `-C opt-level=0` having a sideeffect on another flag should be changed. Having compiler flags affecting others doesn't make much sense to me, they are used to fine tune anyway.
In any case, this plays no role in this PR.
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@nagisa @mystor @daxpedda