"unresolved import" with a circular dependency between modules

Question

I have two files :

json.rs in which I call Builder, a struct defined in builder.rs
builder.rs in which I call Json, a struct defined in json.rs

As you can see there is a circular dependency between these two modules. It seems like sometimes Rust supports circular dependencies, but for this case, the compiler throws errors:

src/json/mod.rs:1:25: 1:31 error: unresolved import (maybe you meant `ToJson::*`?)
src/json/mod.rs:1 pub use self::to_json::{ToJson};
                                          ^~~~~~
src/json/builder.rs:2:18: 2:22 error: unresolved import (maybe you meant `Json::*`?)
src/json/builder.rs:2 use json::json::{Json, JsonEvent, Array, Object}; //commenting this line solve the dependency error

[...]

The code is here in the branch json_mod. I tried to reproduce the problem in fewer lines of code, but the circular dependencies I created compiled correctly.

After the debugging, something like 400 errors are left — this is normal as I am in the process of a huge code refactoring (splitting one file of ~= 4000 line file into many files) and I still have a lot of work to do before making it work.

I can't speak to this specific issue, but I would definitely recommend trying to find a refactoring approach that lets you use smaller steps. You'd have to make a lot of changes between working compilations to fix 400+ errors... — anderspitman
– anderspitman, Commented May 2, 2015 at 18:17

Shepmaster · Accepted Answer · 2015-10-01 14:04:09Z

5

Edit: Glorious news, the bug mentioned below is fixed! It's fixed in Rust 1.4 or later.

Glob imports (use foo::*) have a known bug where they are incompatible with cyclic imports. I would try removing the glob imports in both affected modules.

edited Oct 1, 2015 at 14:04

Shepmaster

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answered May 2, 2015 at 20:58

bluss

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3 Comments

bluss Over a year ago

I thought I saw use std::io::prelude::* in both modules. I'm not 100% it will work, but this is the hunch I have.

Moebius Over a year ago

Link to the rust issue describing it : github.com/rust-lang/rust/issues/4865

bluss Over a year ago

great! Thanks for the link, I didn't find it.

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