Add testing infrastructure for type inference

- move dir_tests to test_utils for that.

crates/test_utils/src/lib.rs

@@ -1,4 +1,6 @@
 use std::fmt;
+use std::fs;
+use std::path::{Path, PathBuf};
 
 use itertools::Itertools;
 use text_unit::{TextRange, TextUnit};
@@ -262,3 +264,100 @@ pub fn find_mismatch<'a>(expected: &'a Value, actual: &'a Value) -> Option<(&'a
         _ => Some((expected, actual)),
     }
 }
+
+pub fn dir_tests<F>(test_data_dir: &Path, paths: &[&str], f: F)
+where
+    F: Fn(&str, &Path) -> String,
+{
+    for (path, input_code) in collect_tests(test_data_dir, paths) {
+        let parse_tree = f(&input_code, &path);
+        let path = path.with_extension("txt");
+        if !path.exists() {
+            println!("\nfile: {}", path.display());
+            println!("No .txt file with expected result, creating...\n");
+            println!("{}\n{}", input_code, parse_tree);
+            fs::write(&path, &parse_tree).unwrap();
+            panic!("No expected result")
+        }
+        let expected = read_text(&path);
+        let expected = expected.as_str();
+        let parse_tree = parse_tree.as_str();
+        assert_equal_text(expected, parse_tree, &path);
+    }
+}
+
+pub fn collect_tests(test_data_dir: &Path, paths: &[&str]) -> Vec<(PathBuf, String)> {
+    paths
+        .iter()
+        .flat_map(|path| {
+            let path = test_data_dir.to_owned().join(path);
+            test_from_dir(&path).into_iter()
+        })
+        .map(|path| {
+            let text = read_text(&path);
+            (path, text)
+        })
+        .collect()
+}
+
+fn test_from_dir(dir: &Path) -> Vec<PathBuf> {
+    let mut acc = Vec::new();
+    for file in fs::read_dir(&dir).unwrap() {
+        let file = file.unwrap();
+        let path = file.path();
+        if path.extension().unwrap_or_default() == "rs" {
+            acc.push(path);
+        }
+    }
+    acc.sort();
+    acc
+}
+
+pub fn project_dir() -> PathBuf {
+    let dir = env!("CARGO_MANIFEST_DIR");
+    PathBuf::from(dir)
+        .parent()
+        .unwrap()
+        .parent()
+        .unwrap()
+        .to_owned()
+}
+
+/// Read file and normalize newlines.
+///
+/// `rustc` seems to always normalize `\r\n` newlines to `\n`:
+///
+/// ```
+/// let s = "
+/// ";
+/// assert_eq!(s.as_bytes(), &[10]);
+/// ```
+///
+/// so this should always be correct.
+pub fn read_text(path: &Path) -> String {
+    fs::read_to_string(path)
+        .expect(&format!("File at {:?} should be valid", path))
+        .replace("\r\n", "\n")
+}
+
+const REWRITE: bool = false;
+
+fn assert_equal_text(expected: &str, actual: &str, path: &Path) {
+    if expected == actual {
+        return;
+    }
+    let dir = project_dir();
+    let pretty_path = path.strip_prefix(&dir).unwrap_or_else(|_| path);
+    if expected.trim() == actual.trim() {
+        println!("whitespace difference, rewriting");
+        println!("file: {}\n", pretty_path.display());
+        fs::write(path, actual).unwrap();
+        return;
+    }
+    if REWRITE {
+        println!("rewriting {}", pretty_path.display());
+        fs::write(path, actual).unwrap();
+        return;
+    }
+    assert_eq_text!(expected, actual, "file: {}", pretty_path.display());
+}