Factor out the mdtest crate (#24616)

Summary
--

This is a first step toward adding mdtests for Ruff. I actually wrote
the code
in the opposite order, first copy-pasting `ty_test` to a `ruff_test`
crate, and then
factoring out the shared code, but I figured it would be easier to
review in
this order. I also opened a stacked PR with the `ruff_test` changes
(#24617)
to show that the API works well for that too.

The main change here is moving several of the modules from `ty_test` to
a new
`mdtest` crate:
- `assertion`
- `diagnostic`
- `matcher`
- `parser`

Beyond moving these files to the new crate, I made `Matcher` functions
take a
`&dyn Db` to support passing a different concrete type from `ruff_test`,
and I
also made the parser generic over an `MdtestConfig` trait to allow Ruff
to use a
separate config struct. I also introduced new `TestConfig` and `TestDb`
types to allow
testing the `matcher` and `parser` within the `mdtest` crate without
depending
on either the real ty `Db` or `ty_test` config type.

The lib.rs file from `ty_test` was essentially split in half, with the
shared
code moved to the `mdtest` crate and the ty-specific parts kept in
`ty_test`.

Test Plan
--

All existing mdtests and the unit tests from `ty_test` should still
pass, and
the stacked branch with the `ruff_test` crate tests the split API

Author: ntBre

Cargo.lock

@@ -57,6 +57,8 @@ ty_static = { path = "crates/ty_static" }
 ty_test = { path = "crates/ty_test" }
 ty_vendored = { path = "crates/ty_vendored" }
 
+mdtest = { path = "crates/mdtest" }
+
 aho-corasick = { version = "1.1.3" }
 anstream = { version = "1.0.0" }
 anstyle = { version = "1.0.10" }

Cargo.toml

@@ -0,0 +1,44 @@
+[package]
+name = "mdtest"
+version = "0.0.0"
+publish = false
+edition.workspace = true
+rust-version.workspace = true
+homepage.workspace = true
+documentation.workspace = true
+repository.workspace = true
+authors.workspace = true
+license.workspace = true
+
+[lib]
+doctest = false
+
+[dependencies]
+ruff_db = { workspace = true }
+ruff_diagnostics = { workspace = true }
+ruff_index = { workspace = true }
+ruff_python_ast = { workspace = true }
+ruff_python_trivia = { workspace = true }
+ruff_source_file = { workspace = true }
+ruff_text_size = { workspace = true }
+
+anyhow = { workspace = true }
+camino = { workspace = true }
+colored = { workspace = true }
+indexmap = { workspace = true }
+insta = { workspace = true }
+memchr = { workspace = true }
+path-slash = { workspace = true }
+regex = { workspace = true }
+rustc-hash = { workspace = true }
+rustc-stable-hash = { workspace = true }
+salsa = { workspace = true }
+serde = { workspace = true }
+similar = { workspace = true }
+smallvec = { workspace = true }
+thiserror = { workspace = true }
+toml = { workspace = true }
+tracing = { workspace = true }
+
+[lints]
+workspace = true

crates/mdtest/Cargo.toml

@@ -497,30 +497,16 @@ pub(crate) enum ErrorAssertionParseError<'a> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::Db;
+    use crate::tests::TestDb;
+    use ruff_db::files::system_path_to_file;
     use ruff_db::parsed::parsed_module;
     use ruff_db::source::line_index;
     use ruff_db::system::DbWithWritableSystem as _;
-    use ruff_db::{Db as _, files::system_path_to_file};
     use ruff_python_trivia::textwrap::dedent;
     use ruff_source_file::OneIndexed;
-    use ty_module_resolver::SearchPathSettings;
-    use ty_python_core::platform::PythonPlatform;
-    use ty_python_core::program::{FallibleStrategy, Program, ProgramSettings};
-    use ty_python_semantic::PythonVersionWithSource;
 
     fn get_assertions(source: &str) -> InlineFileAssertions<'_> {
-        let mut db = Db::setup();
-
-        let settings = ProgramSettings {
-            python_version: PythonVersionWithSource::default(),
-            python_platform: PythonPlatform::default(),
-            search_paths: SearchPathSettings::new(Vec::new())
-                .to_search_paths(db.system(), db.vendored(), &FallibleStrategy)
-                .unwrap(),
-        };
-        Program::init_or_update(&mut db, settings);
-
+        let mut db = TestDb::setup();
         db.write_file("/src/test.py", source).unwrap();
         let file = system_path_to_file(&db, "/src/test.py").unwrap();
         let parsed = parsed_module(&db, file).load(&db);

crates/ty_test/src/assertion.rs crates/mdtest/src/assertion.rscrates/ty_test/src/assertion.rs renamed to crates/mdtest/src/assertion.rs

@@ -140,17 +140,18 @@ struct DiagnosticWithLine<'a> {
 
 #[cfg(test)]
 mod tests {
-    use crate::db::Db;
     use ruff_db::diagnostic::{Annotation, Diagnostic, DiagnosticId, LintName, Severity, Span};
     use ruff_db::files::system_path_to_file;
     use ruff_db::source::line_index;
     use ruff_db::system::DbWithWritableSystem as _;
     use ruff_source_file::OneIndexed;
     use ruff_text_size::{TextRange, TextSize};
 
+    use crate::tests::TestDb;
+
     #[test]
     fn sort_and_group() {
-        let mut db = Db::setup();
+        let mut db = TestDb::setup();
         db.write_file("/src/test.py", "one\ntwo\n").unwrap();
         let file = system_path_to_file(&db, "/src/test.py").unwrap();
         let lines = line_index(&db, file);