Unexpected token: expected `;`, found `#`. #106020

Jerrody · 2022-12-21T22:10:06Z

#[cfg(feature = "validation")]
[debug_utils_ext, (*surface_extensions).to_owned()].concat()

#[cfg(not(feature = "validation"))]
surface_extensions.to_owned()

Error code:

error: expected `;`, found `#`
  --> src\engine\renderer\context\instance.rs:44:73
   |
44 |             [debug_utils_ext, (*surface_extensions).to_owned()].concat()
   |                                                                         ^ help: add `;` here
45 |
46 |             #[cfg(not(feature = "validation"))]
   |             - unexpected token

Metadata:

rustc 1.67.0-nightly (e1d819583 2022-12-05)
binary: rustc
commit-hash: e1d819583f0bf13b016b119c1c2c43e6d3979450
commit-date: 2022-12-05
host: x86_64-pc-windows-msvc
release: 1.67.0-nightly
LLVM version: 15.0.4

The text was updated successfully, but these errors were encountered:

compiler-errors · 2022-12-21T22:42:50Z

What is the issue you are reporting here @Jerrody ?

Jerrody · 2022-12-21T22:49:24Z

What is the issue you are reporting here @Jerrody ?

Well, I thought that compiler can understand that #[cfg()] is related to the block of code, but it fails.

Noratrieb · 2022-12-22T06:32:59Z

Can you post a minimal reproducible example that demonstrates your issue? Or at least mention exactly what you'd expect to happen and why.

Even code that is cfged out is still required to parse successfully.

Jerrody · 2022-12-22T08:36:03Z

Can you post a minimal reproducible example that demonstrates your issue? Or at least mention exactly what you'd expect to happen and why.

Even code that is cfged out is still required to parse successfully.

Let's show you what exactly problem I have.
Full code:

let instance_extensions = {
    let surface_extensions =
        ash_window::enumerate_required_extensions(window.raw_display_handle()).track()?;

    #[cfg(feature = "validation")]
    let debug_utils_ext = vec![ash::extensions::ext::DebugUtils::name().as_ptr()];

    #[cfg(feature = "validation")]
    [debug_utils_ext, (*surface_extensions).to_owned()].concat()

    #[cfg(not(feature = "validation"))]
    surface_extensions.to_owned()
};

And I get this error:

error: expected `;`, found `#`
  --> src\engine\renderer\context\instance.rs:44:73
   |
44 |             [debug_utils_ext, (*surface_extensions).to_owned()].concat()
   |                                                                         ^ help: add `;` here
45 |
46 |             #[cfg(not(feature = "validation"))]
   |             - unexpected token

SkiFire13 · 2022-12-22T09:08:15Z

You seem to already have posted this in this discussion in the internals forum a month ago. What you're asking seems a rather big change to me, I'm not that familiar with how the compiler parser works but I believe it currently requires your program syntax to be correct before #[cfg(...)] macros are expanded, which is not true for your example, so some fundamental changes would be needed.

Jerrody · 2022-12-22T09:53:01Z

You seem to already have posted this in this discussion in the internals forum a month ago. What you're asking seems a rather big change to me, I'm not that familiar with how the compiler parser works but I believe it currently requires your program syntax to be correct before #[cfg(...)] macros are expanded, which is not true for your example, so some fundamental changes would be needed.

Oh, damn, sorry. I totally forgot that I made a post.
Well, if it's not a bug and parser works like this it is bad, anyway, exists alternative way to write like this.
But for me my issue is a candidate to feature request or a bug. Anyway, I'm not a lang dev, so I don't know what scales of this defect (?).

lukas-code · 2022-12-22T13:11:36Z

The workaround for this is to wrap the expressions in a block:

let instance_extensions = {
    let surface_extensions =
        ash_window::enumerate_required_extensions(window.raw_display_handle()).track()?;

    #[cfg(feature = "validation")]
    let debug_utils_ext = vec![ash::extensions::ext::DebugUtils::name().as_ptr()];

    #[cfg(feature = "validation")]
    { [debug_utils_ext, (*surface_extensions).to_owned()].concat() }

    #[cfg(not(feature = "validation"))]
    { surface_extensions.to_owned() }
};

Jerrody · 2022-12-22T23:11:21Z

The workaround for this is to wrap the expressions in a block:

let instance_extensions = {
    let surface_extensions =
        ash_window::enumerate_required_extensions(window.raw_display_handle()).track()?;

    #[cfg(feature = "validation")]
    let debug_utils_ext = vec![ash::extensions::ext::DebugUtils::name().as_ptr()];

    #[cfg(feature = "validation")]
    { [debug_utils_ext, (*surface_extensions).to_owned()].concat() }

    #[cfg(not(feature = "validation"))]
    { surface_extensions.to_owned() }
};

I solved this issue exactly as you did.

albertlarsan68 · 2022-12-23T07:16:59Z

Another way to do this is using the cfg! macro and if ... else.
I personally thinks it is more clear, and should optimize the same.

let instance_extensions = {
    let surface_extensions =
        ash_window::enumerate_required_extensions(window.raw_display_handle()).track()?;

    #[cfg(feature = "validation")]
    let debug_utils_ext = vec![ash::extensions::ext::DebugUtils::name().as_ptr()];

    if cfg!(feature = "validation") {
        [debug_utils_ext, (*surface_extensions).to_owned()].concat()
    } else {
        surface_extensions.to_owned()
    }
};

Jerrody · 2022-12-24T14:35:34Z

Another way to do this is using the cfg! macro and if ... else. I personally thinks it is more clear, and should optimize the same.

let instance_extensions = {
    let surface_extensions =
        ash_window::enumerate_required_extensions(window.raw_display_handle()).track()?;

    #[cfg(feature = "validation")]
    let debug_utils_ext = vec![ash::extensions::ext::DebugUtils::name().as_ptr()];

    if cfg!(feature = "validation") {
        [debug_utils_ext, (*surface_extensions).to_owned()].concat()
    } else {
        surface_extensions.to_owned()
    }
};

Work is not the same, due to cfg! compile-time evaluating an expression that we pass in it and evaluates only it, but at the same time everything compiles what is inside of if else.

Handle attempts to have multiple `cfg`d tail expressions When encountering code that seems like it might be trying to have multiple tail expressions depending on `cfg` information, suggest alternatives that will success to parse. ```rust fn foo() -> String { #[cfg(feature = "validation")] [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>() #[cfg(not(feature = "validation"))] String::new() } ``` ``` error: expected `;`, found `#` --> $DIR/multiple-tail-expr-behind-cfg.rs:5:64 | LL | #[cfg(feature = "validation")] | ------------------------------ only `;` terminated statements or tail expressions are allowed after this attribute LL | [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>() | ^ expected `;` here LL | #[cfg(not(feature = "validation"))] | - unexpected token | help: add `;` here | LL | [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>(); | + help: alternatively, consider surrounding the expression with a block | LL | { [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>() } | + + help: it seems like you are trying to provide different expressions depending on `cfg`, consider using `if cfg!(..)` | LL ~ if cfg!(feature = "validation") { LL ~ [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>() LL ~ } else if cfg!(not(feature = "validation")) { LL ~ String::new() LL + } | ``` Fix rust-lang#106020. r? `@oli-obk`

Rollup merge of rust-lang#117988 - estebank:issue-106020, r=cjgillot Handle attempts to have multiple `cfg`d tail expressions When encountering code that seems like it might be trying to have multiple tail expressions depending on `cfg` information, suggest alternatives that will success to parse. ```rust fn foo() -> String { #[cfg(feature = "validation")] [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>() #[cfg(not(feature = "validation"))] String::new() } ``` ``` error: expected `;`, found `#` --> $DIR/multiple-tail-expr-behind-cfg.rs:5:64 | LL | #[cfg(feature = "validation")] | ------------------------------ only `;` terminated statements or tail expressions are allowed after this attribute LL | [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>() | ^ expected `;` here LL | #[cfg(not(feature = "validation"))] | - unexpected token | help: add `;` here | LL | [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>(); | + help: alternatively, consider surrounding the expression with a block | LL | { [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>() } | + + help: it seems like you are trying to provide different expressions depending on `cfg`, consider using `if cfg!(..)` | LL ~ if cfg!(feature = "validation") { LL ~ [1, 2, 3].iter().map(|c| c.to_string()).collect::<String>() LL ~ } else if cfg!(not(feature = "validation")) { LL ~ String::new() LL + } | ``` Fix rust-lang#106020. r? `@oli-obk`

Jerrody added the C-bug Category: This is a bug. label Dec 21, 2022

Jerrody changed the title ~~Unexpected token: expected ;, found #`.~~ Unexpected token: expected ;, found #. Dec 21, 2022

estebank added A-parser Area: The parsing of Rust source code to an AST T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. D-confusing Diagnostics: Confusing error or lint that should be reworked. and removed C-bug Category: This is a bug. labels Mar 14, 2023

estebank mentioned this issue Nov 16, 2023

Handle attempts to have multiple cfgd tail expressions #117988

Merged

bors closed this as completed in a16722d Nov 20, 2023

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Unexpected token: expected `;`, found `#`. #106020

Unexpected token: expected `;`, found `#`. #106020

Jerrody commented Dec 21, 2022

compiler-errors commented Dec 21, 2022

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Noratrieb commented Dec 22, 2022 •

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SkiFire13 commented Dec 22, 2022

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lukas-code commented Dec 22, 2022

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albertlarsan68 commented Dec 23, 2022

Jerrody commented Dec 24, 2022

Unexpected token: expected ;, found #. #106020

Unexpected token: expected ;, found #. #106020

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Jerrody commented Dec 21, 2022

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Jerrody commented Dec 24, 2022

Unexpected token: expected `;`, found `#`. #106020

Unexpected token: expected `;`, found `#`. #106020

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