Show faulty line in DifferencePredicate

[Chewie]

Heya,

The regular assert_eq! macro provides the line containing the assert in its output:

thread 'main' panicked at 'assertion failed:  `(left == right)`
  left: `4`,
 right: `2`, tests/test.rs:112:5

This information can be parsed by editors like Vim to fill the quickfix list automatically and jump to the error, which is very helpful.

Unfortunately, the DifferencePredicate doesn't show this information:

---- test_no_yaml stdout ----
thread 'main' panicked at 'Unexpected stdout, failed diff var original
├── original: No test case found. Exuting.

├── diff: 
--- value	expected
+++ value	actual
@@ -1 +1 @@
-No test case found. Exuting.
+No test case found. Exiting.

└── var as str: No test case found. Exiting.

Would it be possible to add this information to the output?

[Chewie]

I've been playing with similar and it's companion similar-asserts as a replacement of differences.rs, and the result is very clean. Maybe the predicate could make use of this crate?

[epage]

This crate aims to be the low level mechanism for implementing crates like that, like assert_that or assert_cmd.

To get this functionality, it either needs to come via a macro or the recent https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1460-2020-08-27 attribute

For my crates, I've created assert-rs/assert_cmd#133 and assert-rs/assert_fs#68