Hello, When using this function directly or automatically through flycheck it blocks up the UI for a few seconds. Is it possible to make this not block?

Suspicious state from syntax checker rust-cargo: Checker rust-cargo returned non-zero exit code 101, but no errors from output: extra arguments to `rustc` can only be passed to one target, consider filtering
the package by passing e.g. `--lib` or `--bin NAME` to specify a single target

I believe this is related to #16 and #18. I'm using the latest version from Dec 25 and getting this message when I save any file on my project. The project layout is:

src/
├── config.rs
├── error.rs
├── lib.rs
├── main.rs

Any ideas about this? Is there something I'm doing wrong?

Thank you.

Don't guess, use Cargo's own settings. Blocked by https://github.com/rust-lang/cargo/pull/1434

Specifically: Extract the layout, the crate roots, the dependencies, and probably compiler flags as well. Will probably require changes to Flycheck's rust checker, to pass additional flags.

Fixes: #5, #7, probably #11

Hello,

I have the following code which compiles fine via cargo run:

src/main.rs

extern crate rand;

use rand::distributions::{IndependentSample, Range};

fn main() {
    let mut rng = rand::thread_rng(); // Flycheck error is here
    let range = Range::new(-512.03, 511.97);
    println!("A random number is {}", range.ind_sample(&mut rng));
}

Cargo.toml

[package]
name = "rando"
version = "0.1.0"
authors = ["Andrew Schwartzmeyer <[email protected]>"]

[dependencies]
rand = "0.3"

However, Flycheck with flycheck-rust gives the warning "unresolved name rand::thread_rng" on line 6. It does not appear to be recognize that the function was imported from a crate.

The Flycheck project may be a better place to post this issue, but I was hoping you could help me out!

rustc 1.0.0 (a59de37e9 2015-05-13) (built 2015-05-14)
cargo 0.2.0-nightly (efb482d 2015-04-30) (built 2015-04-29)
OS X 10.10.3
GNU Emacs 24.5.50.1 (x86_64-apple-darwin14.3.0, NS apple-appkit-1347.57) of 2015-04-13
Flycheck version: 0.24snapshot (package: 20150514.528)
flycheck-rust package 20150417.1048

I am using the rand crate.

Hi.

When running flycheck-rust-setup I get this error everytime. Then flycheck checks nothing, nothing is underlined and running flycheck-buffer manually does nothing (no error).

This PR is there to start a discussion on the basis of a working implementation, but is not meant to merge as-is until the discussion is over.

The gist of it is that I'm proposing to:

1. Use cargo (and only cargo) to find the build target for the current file, and set the variables used by rust-cargo accordingly.
2. Leave the rust checker for single rust files, which means not setting up any variables for it in flycheck-rust.

And as I'm unsure whether this will break anyone's setup, I'm asking for feedback.

cc @flycheck/rust

Read on for the details.

To fix #38, I figured I might as well clean up the logic a bit in flycheck-rust, which was getting a bit redundant. Originally, it seems we used various methods to get the information to pass to the rustc checker in order to be able to check single rust files. Then we started to use cargo directly to get this information, and now we have two ways of doing things. I think that #8 intended for cargo to be the main way to extract the information needed to run the rust checkers, and this PR aims to do that.

As I understand it, the role of flycheck-rust is to set the variables used by the rust checkers in flycheck, so the checkers can produce meaningful errors for the current file. The rust checkers (especially rust-cargo) won't actually do anything without the proper variables set first, especially flycheck-rust-crate-type and flycheck-rust-binary-name. These variables could also be set directly by the user, by file-local variables or .dir-locals.el or any other means. Flycheck-rust will just try to set them when their value can be found automatically.

Also, I understand there's a slight mismatch between flycheck checkers that are meant to run on single files, but cargo only builds targets, not individual files. We cannot point cargo to the file X and say "give me the compilation errors for X". We have to say "give me compilation errors for the binary crate Y", where crate Y contains and makes use of the file X, and we will get errors for X (among all the other files in Y). The problem with that is that we have no way to know for sure that file X is part of crate Y. cargo won't tell us, and we would need to resolve the imports and build a dependency graph to know the answer; that's certainly out of scope. The only cases where we can be certain is when cargo read-manifest gives us the exact filenames for targets. Other than that, we can make educated guesses based on the conventional cargo layout (e.g., any file under src/ other than src/main.rs contribute to the library target). These guesses may fail if the project actually does not follow the convention, but then the user can always override these guesses with local variables.

I set up a test crate, added all the relevant test cases from the conventional cargo layout I could find, and just used cargo to find the correct target to build based on the buffer filename. Even when deleting most of the code, it just works and sets up the flycheck-rust-crate-type and flycheck-rust-binary-name correctly for all the test cases.

This fixes #38, increases our coverage, and gets rid of most of the code. However, I don't know if I've broken anything else, especially for the plain rust checker.

I left out setting these variables:

• flycheck-rust-crate-root is unneeded for rust-cargo and might just be redundant with flycheck-rust-binary-name
• flycheck-rust-check-tests: I don't understand why we would skip tests in executables. It's less surprising if all the code is checked, including code behind the #[cfg(test)] feature.
• flycheck-rust-library-path is unneeded for rust-cargo as well, as cargo already handles passing the dependencies to rustc. It certainly is needed for the rust checker, but only when building crates, which brings me to the last point.

As I gathered from #8, the use case for the bare rust checker is to check single files that are not part of a cargo project (like StackOverflow answers, or minimal working examples), leaving the rust-cargo checker for pretty much anything else. Though if that is the case, I don't understand why we we pass the variable flycheck-rust-crate-type to rustc in the rust checker, or flycheck-rust-library-path, especially as we have flycheck-rust-args to already pass arbitrary arguments to rustc. That may be a separate PR to flycheck if it turns out these variables are indeed superfluous.

Note: an alternative would be to add the ability to cargo to give us a list of build targets a file is associated with. That way, we could just get rid of flycheck-rust altogether and just invoke that new command in rust-cargo directly. I don't know if the cargo maintainers would be open to it, or how complex it would be to implement (I'm guessing not much, since the dependency information should already be available, but I haven't checked).

Syntax checkers for buffer main.rs in rust-mode:

  rust-cargo
    - may enable:  yes
    - predicate:   t
    - executable:  Found at /Users/zwb/.cargo/bin/cargo
    - Cargo.toml:  Found
    - Crate type:  bin
    - Binary name: iron-gcd

  rust
    - may enable: yes
    - predicate:  t
    - executable: Found at /Users/zwb/.cargo/bin/rustc

  rust-clippy (disabled)
    - may enable: Automatically disabled!
    - predicate:  t
    - executable: Found at /Users/zwb/.cargo/bin/cargo
    - Clippy:     Cannot find the `cargo clippy' command
    - Cargo.toml: Found

Flycheck Mode is enabled. Use SPC u C-c ! x to enable disabled checkers.

--------------------

Flycheck version: 32snapshot
Emacs version:    25.3.1
System:           x86_64-apple-darwin17.3.0
Window system:    mac

I'm getting the following errors when opening a Rust buffer:

Error in flycheck-rust-setup: (invalid-function (packages (let-alist (with-temp-buffer (call-process cargo nil t nil "metadata" "--no-deps" "--manifest-path" manifest) (goto-char (point-min)) (let ((json-array-type (quote list))) (json-read))) \.packages)))
Suspicious state from syntax checker rust-cargo: Flycheck checker rust-cargo returned non-zero exit code 101, but its output contained no errors: error: no library targets found

Try installing a more recent version of rust-cargo, and please open a bug report if the issue persists in the latest release.  Thanks!

My init.el setup:

(use-package rust-mode
  :defer t
  :mode "\\.rs\\'"
  :config (setq rust-format-on-save t)
  )

;; Run cargo commands in rust buffers, e.g. C-c C-c C-r for cargo-run
(use-package cargo
  :init
  (add-hook 'rust-mode-hook 'cargo-minor-mode)
  (add-hook 'toml-mode-hook 'cargo-minor-mode)
  )

(use-package racer
  :init
  (add-hook 'rust-mode-hook #'racer-mode)
  (add-hook 'racer-mode-hook #'eldoc-mode)
  :config
  (define-key rust-mode-map (kbd "TAB") #'company-indent-or-complete-common)
  (setq racer-rust-src-path "/usr/local/src/rust/src")
  )

;; Doesn't work, json-read-error
(use-package flycheck-rust
  :init
  (add-hook 'flycheck-mode-hook #'flycheck-rust-setup))

Running flycheck-verify-setup:

Syntax checkers for buffer main.rs in rust-mode:

  rust-cargo
    - may enable:  yes
    - predicate:   t
    - executable:  Found at /usr/local/bin/cargo
    - Cargo.toml:  Found
    - Crate type:  lib
    - Binary name: Not required

  rust
    - may enable: yes
    - predicate:  t
    - executable: Found at /usr/local/bin/rustc

Flycheck Mode is enabled. Use C-u C-c ! x to enable disabled checkers.

--------------------

Flycheck version: 31snapshot (package: 20170324.340)
Emacs version:    26.0.50
System:           x86_64-pc-linux-gnu
Window system:    x

flycheck-rust reports this error whenever I open a rust file.

The file src/main.rs exists and is the file I am currently opening. Do I miss some config here?

I am using only rust-mode and flycheck-rust from melpa, with:

(require 'sm-flycheck)

(add-hook 'rust-mode-hook 'flycheck-mode)
(add-hook 'flycheck-mode-hook #'flycheck-rust-setup)
(add-hook 'rust-mode-hook 'subword-mode)

Thanks

It seems that flycheck-rust only checks syntax when the file is saved, even if the appropriate variables are present in flycheck-check-syntax-automatically.

Its value is (save idle-change new-line mode-enabled), and yet idle-change and new-line don't trigger the syntax check.

Because when I try check projects without lib.rs (only main.rs) I got this on C-c ! C-c rust-cargo RET on any file:

-*- mode: compilation; default-directory: "~/Desktop/project-church/src/" -*-
Compilation started at Sat Jul 15 22:00:17

cargo rustc --lib --message-format\=json -- -Z no-trans --test
error: no library targets found

Compilation exited abnormally with code 101 at Sat Jul 15 22:00:17

Hi I am using doom emacs and my configuration is simple

(rust +lsp) in init.el

(use-package! rustic)

that is it, But i got an error Error in rustic-flycheck-setup: (user-error "flycheck-rust cannot find ‘cargo’. Please make sure that cargo is installed and on your PATH.

how can I solve this problem?

json-read from json.el can return a non-alist value when json-object-type is set to a value distinct from 'alist. Since the let-alist macro expects to receive an alist, flycheck-rust-get-cargo-targets will raise a wrong-type-argument error and prevent flycheck-rust from loading when json-object-type is not 'alist. (In my case, json-object-type was set to 'hash-table either by default or by some other package.)