Add OsSystem support to mdtests (#16518)

## Summary

This PR introduces a new mdtest option `system` that can either be
`in-memory` or `os`
where `in-memory` is the default.

The motivation for supporting `os` is so that we can write OS/system
specific tests
with mdtests. Specifically, I want to write mdtests for the module
resolver,
testing that module resolution is case sensitive. 

## Test Plan

I tested that the case-sensitive module resolver test start failing when
setting `system = "os"`

Author: MichaReiser

Cargo.lock

@@ -255,7 +255,7 @@ mod tests {
     use crate::files::Index;
     use crate::ProjectMetadata;
     use ruff_db::files::system_path_to_file;
-    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+    use ruff_db::system::{DbWithWritableSystem as _, SystemPathBuf};
     use ruff_python_ast::name::Name;
 
     #[test]

crates/red_knot_project/src/files.rs

@@ -528,7 +528,7 @@ mod tests {
     use ruff_db::diagnostic::OldDiagnosticTrait;
     use ruff_db::files::system_path_to_file;
     use ruff_db::source::source_text;
-    use ruff_db::system::{DbWithTestSystem, SystemPath, SystemPathBuf};
+    use ruff_db::system::{DbWithTestSystem, DbWithWritableSystem as _, SystemPath, SystemPathBuf};
     use ruff_db::testing::assert_function_query_was_not_run;
     use ruff_python_ast::name::Name;
 

crates/red_knot_project/src/lib.rs

@@ -321,7 +321,7 @@ mod tests {
 
         system
             .memory_file_system()
-            .write_files([(root.join("foo.py"), ""), (root.join("bar.py"), "")])
+            .write_files_all([(root.join("foo.py"), ""), (root.join("bar.py"), "")])
             .context("Failed to write files")?;
 
         let project =
@@ -349,7 +349,7 @@ mod tests {
 
         system
             .memory_file_system()
-            .write_files([
+            .write_files_all([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -393,7 +393,7 @@ mod tests {
 
         system
             .memory_file_system()
-            .write_files([
+            .write_files_all([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -432,7 +432,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files([
+            .write_files_all([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -482,7 +482,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files([
+            .write_files_all([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -532,7 +532,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files([
+            .write_files_all([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -572,7 +572,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files([
+            .write_files_all([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -623,7 +623,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files([
+            .write_files_all([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -673,7 +673,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -703,7 +703,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -735,7 +735,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -765,7 +765,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -795,7 +795,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -828,7 +828,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -861,7 +861,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -886,7 +886,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -911,7 +911,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file(
+            .write_file_all(
                 root.join("pyproject.toml"),
                 r#"
                 [project]

crates/red_knot_project/src/metadata.rs

@@ -117,7 +117,7 @@ fn run_corpus_tests(pattern: &str) -> anyhow::Result<()> {
         let code = std::fs::read_to_string(source)?;
 
         let mut check_with_file_name = |path: &SystemPath| {
-            memory_fs.write_file(path, &code).unwrap();
+            memory_fs.write_file_all(path, &code).unwrap();
             File::sync_path(&mut db, path);
 
             // this test is only asserting that we can pull every expression type without a panic

crates/red_knot_project/tests/check.rs

@@ -1,6 +1,11 @@
 # Case Sensitive Imports
 
-TODO: This test should use the real file system instead of the memory file system.
+```toml
+# TODO: This test should use the real file system instead of the memory file system.
+# but we can't change the file system yet because the tests would then start failing for 
+# case-insensitive file systems.
+#system = "os"
+```
 
 Python's import system is case-sensitive even on case-insensitive file system. This means, importing
 a module `a` should fail if the file in the search paths is named `A.py`. See

crates/red_knot_python_semantic/resources/mdtest/import/case_sensitive.md

@@ -25,7 +25,9 @@ pub(crate) mod tests {
     use crate::lint::{LintRegistry, RuleSelection};
     use anyhow::Context;
     use ruff_db::files::{File, Files};
-    use ruff_db::system::{DbWithTestSystem, System, SystemPathBuf, TestSystem};
+    use ruff_db::system::{
+        DbWithTestSystem, DbWithWritableSystem as _, System, SystemPathBuf, TestSystem,
+    };
     use ruff_db::vendored::VendoredFileSystem;
     use ruff_db::{Db as SourceDb, Upcast};
     use ruff_python_ast::PythonVersion;

crates/red_knot_python_semantic/src/db.rs

@@ -720,7 +720,7 @@ impl<'db> ResolverContext<'db> {
 #[cfg(test)]
 mod tests {
     use ruff_db::files::{system_path_to_file, File, FilePath};
-    use ruff_db::system::DbWithTestSystem;
+    use ruff_db::system::{DbWithTestSystem as _, DbWithWritableSystem as _};
     use ruff_db::testing::{
         assert_const_function_query_was_not_run, assert_function_query_was_not_run,
     };

crates/red_knot_python_semantic/src/module_resolver/resolver.rs

@@ -1,4 +1,6 @@
-use ruff_db::system::{DbWithTestSystem, SystemPath, SystemPathBuf};
+use ruff_db::system::{
+    DbWithTestSystem as _, DbWithWritableSystem as _, SystemPath, SystemPathBuf,
+};
 use ruff_db::vendored::VendoredPathBuf;
 use ruff_python_ast::PythonVersion;
 

crates/red_knot_python_semantic/src/module_resolver/testing.rs

@@ -409,7 +409,7 @@ impl FusedIterator for ChildrenIter<'_> {}
 mod tests {
     use ruff_db::files::{system_path_to_file, File};
     use ruff_db::parsed::parsed_module;
-    use ruff_db::system::DbWithTestSystem;
+    use ruff_db::system::DbWithWritableSystem as _;
     use ruff_python_ast as ast;
     use ruff_text_size::{Ranged, TextRange};
 
@@ -440,7 +440,7 @@ mod tests {
         file: File,
     }
 
-    fn test_case(content: impl ToString) -> TestCase {
+    fn test_case(content: impl AsRef<str>) -> TestCase {
         let mut db = TestDb::new();
         db.write_file("test.py", content).unwrap();