A Rust Compiler Error I Don't Understand

Scratching My Head

The folks behind the Rust compiler consider it a bug if you hit an error message that doesn't give you enough info to fix it. I just hit one that stumped me.

I'm not exactly sure where to open the ticket. Writing it up here so I can figure that out later.

Here's the error:

Compiling neopolitan v0.2.0 (/Users/alan/workshop/neopolitan)
error: lifetime may not live long enough
  --> src/page/mod.rs:11:5
   |
8  | #[derive(Clone, Debug, Deserialize, Serialize)]
   |                        ----------- lifetime `'de` defined here
9  | pub struct Page<'a> {
   |                 -- lifetime `'a` defined here
10 |     pub source_path: PathBuf,
11 |     pub data: Ast<'a>,
   |     ^^^^^^^^^^^^^^^^^ requires that `'de` must outlive `'a`
   |
   = help: consider adding the following bound: `'de: 'a`

error: could not compile `neopolitan` (lib) due to 2 previous errors
warning: build failed, waiting for other jobs to finish...
error: could not compile `neopolitan` (lib test) due to 2 previous errors
[Command exited with 101]

The problem file is:

src/page/mod.rs

which is being used from:

src/site/mod.rs

The Ast file is:

src/ast/mod.rs

I haven't done anything with it yet. I just created it and immediately ran into the problem.

I don't have the spoons right now to try to extract the error more. Hopefully the issue can be found from the small page file.

What I Tried

The help suggestion says:

consider adding the following bound: `'de: 'a`

But, I'm not sure how to go about that.

This is the original code that's throwing the error:

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct Page<'a> {
    pub source_path: PathBuf,
    pub data: Ast<'a>,
}

Based on the error message, I tried:

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct Page<'a> {
    pub source_path: PathBuf,
    pub data: Ast<'de: 'a>,
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct Page<'a> {
    pub source_path: PathBuf,
    pub data: Ast<'de> 'a>,
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct Page<'de: 'a> {
    pub source_path: PathBuf,
    pub data: Ast<'a>,
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct Page<'de: 'a> {
    pub source_path: PathBuf,
    pub data: Ast<'de: 'a>,
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct Page<'de 'a> {
    pub source_path: PathBuf,
    pub data: Ast<'de 'a>,
}

Those all threw their own error messages. I wasn't able to figure out how to fix it from them either.

Next Steps

I haven't dug much further yet. Wanted to get this down first as a submission about the compiler.

I'll update this when I learn more.

-a

Postscript

Okay, I jumped around the issue for now by updating the Ast to use a String instead of a &str. That got me going, but I'm still going to open the ticket since the confusion was about the compiler message itself and I took a different path that what it suggested.

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