Tracking issue for great error messages about dhall-rust HOT 8 OPEN

I'd like to follow the style of Rust error messages, because they rock.
Note to self: have a look at https://github.com/rust-lang/rust/blob/master/src/librustc_errors/lib.rs

from dhall-rust.

First step done ! #114

from dhall-rust.

Next step: #116

from dhall-rust.

Most of the groundwork is done, now there's mostly a need of writing nice error messages.

from dhall-rust.

The state of error messages can be seen in the .txt files in dhall/tests/.../failure/.... For example:

from dhall-rust.

Errors are not pretty printed in test outputs. It seems like it is attempting to use the Debug version instead. For example this is the output when I tried to create a test case for the issue in #173

---- test_rename_all_camel_case stdout ----
thread 'test_rename_all_camel_case' panicked at 'called `Result::unwrap()` on an `Err` value: Error(Dhall(Error { kind: Typecheck(TypeError { message: Custom("error: annot mismatch: { function : Text, mergeVariant : Optional Text, postVariant : Optional Text, preVariant : Optional Text } != { function : Text, `merge_variant` : Optional Text, `post_variant` : Optional Text, `pre_variant` : Optional Text }\n --> <current file>:2:1\n  |\n... |\n6 | |     }\n  | |______^ annot mismatch: { function : Text, mergeVariant : Optional Text, postVariant : Optional Text, preVariant : Optional Text } != { function : Text, `merge_variant` : Optional Text, `post_variant` : Optional Text, `pre_variant` : Optional Text }\n  |") }) }))', serde_dhall/tests/rename.rs:33:10

from dhall-rust.

You get this output because you used .unwrap() in your test case. .unwrap() will indeed use the Debug impl to display the values, which is not nice here. The way I would do it here is just define a parse function that extracts the error and manually prints is with its Display impl. Something like

fn parse<T: FromDhall + StaticType>(s: &str) -> T {
	match from_str(s).static_type_annotation().parse() {
		Ok(x) => x,
		Err(e) => panic!("{}", e),
	}
}

and then use parse::<Transform>(test_str). It's a bit annoying but the Debug impl is often useful for tricky cases so I want to keep it around.

from dhall-rust.

I created a relevant issue: #228

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