Naga error messages not as useful as they could be

[almarklein]

When the provided WGSL shader code is invalid, the error messages are usually less useful than if I run Naga directly on that shader code.

Example:

...
return vec4<f32>(value, value, value, 1);

wgpu-native:

Vector component[3] type Scalar { kind: Sint, width: 4 }
thread '<unnamed>' panicked at 'Validation(EntryPoint { stage: Fragment, name: "fs_main", error: Function(Expression { handle: [9], error: Compose(ComponentType { index: 3 }) }) })', src\device.rs:87:5

Naga:

Entry point fs_main at Fragment is invalid:
        Expression [9] is invalid
        Composing 3's component type is not expected
error: process didn't exit successfully: `target\debug\naga.exe c:/dev/py/tmp.wgsl` (exit code: 0xffffffff)

With naga it will sometimes also indicate where in the code the error occurs.

Is this something that can be improved somehow?

[kvark]

Absolutely! The error function needs to walk the chain of errors, not just debug print it ({:?}). See https://github.com/gfx-rs/naga/blob/72fca17dbc56a33acdf53ab6eab113386a774731/bin/naga.rs#L26

[almarklein]

Is that link where a change would be needed to fix this, or is this the function that should be called instead in wgpu-core?

[kvark]

This is an example of properly printing out the error chain. wgpu-native need similar logic in order to spew out readable messages.

[almarklein]

I think this is where a change would be needed:

https://github.com/gfx-rs/wgpu/blob/eadaa1b7d8f585761e28445904fe619b180aca0d/wgpu-core/src/device/mod.rs#L1041-L1052

I had a quick try inserting the referenced lines there, but get:

let mut e = err.source();
                ^^^^^^ method not found in `naga::front::wgsl::ParseError

[kvark]

Do you have std::error::Error in scope? Try adding use std::error::Error.

[almarklein]

Ah, that helps getting the code to compile. But the error reporting is not getting better. I just saw this maybe related comment, looks like someone else is trying to achieve something similar for glsl.

[kvark]

Hmm. Error reporting is already there for WGSL though, and this is what you are testing.
What does it look like currently with these changes?

[almarklein]

Here's what I got so far: gfx-rs/wgpu#1424

[almarklein]

This has been fixed upstream.