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Document the -Z flag to the rustc book #59680

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Apr 12, 2019
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Document the -Z flag to the rustc book #59680

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5c7a944
Add documentation on the -Z flag on the command-line arguments sectio…
Apr 3, 2019
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Updated the documentation, now claiming the -Z is associated to unsta…
Apr 10, 2019
cdeb745
Updated the description of -Z in the rustc book.
Apr 10, 2019
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6 changes: 6 additions & 0 deletions src/doc/rustc/src/command-line-arguments.md
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Expand Up @@ -86,6 +86,12 @@ This flag will set which lints should be set to the [deny level](lints/levels.ht

This flag will set which lints should be set to the [forbid level](lints/levels.html#forbid).

## `-Z`: set options for debugging rustc
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So, while it's true that many flags are good for debugging, that's not the purpose of -Z. It's really for unstable compiler flags. It just so happens that debugging is a good use of flags that aren't yet stable.

Could we maybe re-word this?

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Ahh glad you say so! I came to that conclusion by running rustc --help which says:

-Z help             Print internal options for debugging rustc

Maybe this should be changed as well then? What do you think about:

-Z help             Print unstable compiler flags

When running rustc -Z help it also starts with:

Available debug options:
...

Should this be changed into something more generic like "Available options:" as well?

Curious to what you think of all this! Because of these lines I was really under the impression it was for debug options only (even though that seemed a bit weird to me..)

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cc @rust-lang/compiler

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+1 -- these aren't just for debugging, changing the description would make sense to me.

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@steveklabnik @cramertj I updated the descriptions (Y).

I saw that some methods also contained words like "debug_..." but I wasn't brave enough to go and change those as well :)


This flag lets you set options for debugging rustc. In order to set multiple options, the -Z flag
can be used multiple times. For example: `rustc -Z verbose -Z time`. Specifying options with -Z is
only available on nightly. To view all available options run: `rustc -Z help`.

## `--cap-lints`: set the most restrictive lint level

This flag lets you 'cap' lints, for more, [see here](lints/levels.html#capping-lints).
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