feature: debug_string_snapshot to test pretty printers

[honungsburk]

I'm writing a DSL and would like to use insta to snapshot test my pretty printer and my diagnostics messages. Is it already possible somehow and I've just missed it or would debug_string_snapshot make a nice addition to the library?

[max-sixty]

Could you give an example? Would assert_debug_snapshot work?

[honungsburk]

For example, you could have a typescript pretty printer that takes this as input

function  greet(name:string){console.log("Hello, "+name);}const name="Alice";greet(name);

and outputs this:

function greet(name: string): void {
  console.log("Hello, " + name);
}

const name = "Alice";
greet(name);

Then it would be nice to see that the formatting stays the same as you are refactoring.

I think assert_debug_snapshot would work if I created a wrapper struct for String and implemented such that it does not escape newline characters.

However, I have used similar libraries to insta in other languages and they only expected to be given some arbitrary string. I was surprised that this was not directly supported.

[max-sixty]

Can you give a rust code example?

[honungsburk]

I got it working using debug.

The idea is that I want to quickly iterate on the quality of my error messages and it is a pain to run my CLI too all the time (and I want to catch regressions) so I dump a bunch of code for my custom DSL into a directory and then have it check each file individually for errors.

input file:

@doc "hello"
@doc "world"
collection Person {
    name: string
}

output file:

---
source: packages/cli/tests/diagnostics_report_test.rs
assertion_line: 40
expression: PrintString(report_string)
snapshot_kind: text
---
[E0013] Error: Decorator '@doc' is already defined.
   ╭─[/Users/frankhampusweslien/git/frank/graphite-lang/packages/cli/tests/diagnostics_report_input/duplicate_decorator.gr:1:1]
   │
 1 │ @doc "hello"
   │ ──┬─  
   │   ╰─── error here
───╯
[E0013] Error: Decorator '@doc' is already defined.
   ╭─[/Users/frankhampusweslien/git/frank/graphite-lang/packages/cli/tests/diagnostics_report_input/duplicate_decorator.gr:2:1]
   │
 2 │ @doc "world"
   │ ──┬─  
   │   ╰─── error here
───╯

testing code:

use ariadne::FileCache;
use graphite_cli::diagnostics_report;
use graphite_core::pipeline;
use std::path::PathBuf;

struct PrintString(String);

impl std::fmt::Debug for PrintString {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

/// Regression tests for diagnostics report. Run `cargo test` to check that all the tests pass.
#[test]
fn test_parser_regression() {
    let test_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
        .join("tests")
        .join("diagnostics_report_input");

    let mut failures = Vec::new();

    for entry in std::fs::read_dir(test_dir).unwrap() {
        let entry = entry.unwrap();
        let file_name = entry.file_name().to_str().unwrap().to_string();
        let result = std::panic::catch_unwind(|| {
            let file_path = entry.path();

            let diagnostics = pipeline::check(file_path);

            // Build and render the diagnostic report

            let mut buffer = Vec::new();
            for diagnostic in diagnostics {
                let report = diagnostics_report::build(&diagnostic);
                report.write(FileCache::default(), &mut buffer).unwrap();
            }
            let report_string = String::from_utf8(strip_ansi_escapes::strip(&buffer)).unwrap();
            // Assert the snapshot
            insta::assert_debug_snapshot!(file_name.clone(), PrintString(report_string));
        });

        if result.is_err() {
            failures.push(file_name.to_string());
        }
    }

    if !failures.is_empty() {
        panic!("Diagnostic report tests failed for files: {:?}", failures);
    }
}