[ty] Make check_file a salsa query (#19255)

## Summary
We noticed that all files get reparsed when workspace diagnostics are
enabled.

I realised that this is because `check_file_impl` access the parsed
module but itself isn't a salsa query.
This pr makes `check_file_impl` a salsa query, so that we only access
the `parsed_module` when the file actually changed. I decided to remove
the salsa query from `check_types` because most functions it calls are
salsa queries itself and having both `check_types` and `check_file` as
salsa querise has the downside that we double cache the diagnostics.

## Test Plan

**Before**

```
2025-07-10 12:54:16.620766000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c0c))}: File `/Users/micha/astral/test/yaml/yaml-stubs/__init__.pyi` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.621942000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c13))}: File `/Users/micha/astral/test/ignore2 2/nested-repository/main.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.622107000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c09))}: File `/Users/micha/astral/test/notebook.ipynb` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.622357000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c04))}: File `/Users/micha/astral/test/no-trailing.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.622634000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c02))}: File `/Users/micha/astral/test/simple.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.623056000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c07))}: File `/Users/micha/astral/test/open/more.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.623254000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c11))}: File `/Users/micha/astral/test/ignore-bug/backend/src/subdir/log/some_logging_lib.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.623450000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c0f))}: File `/Users/micha/astral/test/yaml/tomllib/__init__.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.624599000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c05))}: File `/Users/micha/astral/test/create.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.624784000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c00))}: File `/Users/micha/astral/test/lib.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.624911000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c0a))}: File `/Users/micha/astral/test/sub/test.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.625032000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c12))}: File `/Users/micha/astral/test/ignore2/nested-repository/main.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.625101000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c08))}: File `/Users/micha/astral/test/open/test.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.625227000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c03))}: File `/Users/micha/astral/test/pseudocode_with_bom.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.625353000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c0b))}: File `/Users/micha/astral/test/yaml/yaml-stubs/loader.pyi` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.625543000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c01))}: File `/Users/micha/astral/test/test_trailing.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.625616000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c0d))}: File `/Users/micha/astral/test/yaml/tomllib/_re.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.625667000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c06))}: File `/Users/micha/astral/test/yaml/main.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.625779000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c10))}: File `/Users/micha/astral/test/yaml/tomllib/_types.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.627526000  WARN request{id=19 method="workspace/diagnostic"}:Project::check:check_file{file=file(Id(c0e))}: File `/Users/micha/astral/test/yaml/tomllib/_parser.py` was reparsed after being collected in the current Salsa revision
2025-07-10 12:54:16.627959000 DEBUG request{id=19 method="workspace/diagnostic"}:Project::check: Checking all files took 0.007s
```

Now, no more logs regarding reparsing

crates/ty_project/src/lib.rs

@@ -257,8 +257,11 @@ impl Project {
                             tracing::debug_span!(parent: project_span, "check_file", ?file);
                         let _entered = check_file_span.entered();
 
-                        let result = self.check_file_impl(&db, file);
-                        file_diagnostics.lock().unwrap().extend(result);
+                        let result = check_file_impl(&db, file);
+                        file_diagnostics
+                            .lock()
+                            .unwrap()
+                            .extend(result.iter().map(Clone::clone));
 
                         reporter.report_file(&file);
                     });
@@ -285,7 +288,7 @@ impl Project {
             return Vec::new();
         }
 
-        self.check_file_impl(db, file)
+        check_file_impl(db, file).iter().map(Clone::clone).collect()
     }
 
     /// Opens a file in the project.
@@ -466,71 +469,73 @@ impl Project {
             self.set_file_set(db).to(IndexedFiles::lazy());
         }
     }
+}
 
-    fn check_file_impl(self, db: &dyn Db, file: File) -> Vec<Diagnostic> {
-        let mut diagnostics: Vec<Diagnostic> = Vec::new();
+#[salsa::tracked(returns(deref), heap_size=get_size2::GetSize::get_heap_size)]
+pub(crate) fn check_file_impl(db: &dyn Db, file: File) -> Box<[Diagnostic]> {
+    let mut diagnostics: Vec<Diagnostic> = Vec::new();
 
-        // Abort checking if there are IO errors.
-        let source = source_text(db, file);
+    // Abort checking if there are IO errors.
+    let source = source_text(db, file);
 
-        if let Some(read_error) = source.read_error() {
-            diagnostics.push(
-                IOErrorDiagnostic {
-                    file: Some(file),
-                    error: read_error.clone().into(),
-                }
-                .to_diagnostic(),
-            );
-            return diagnostics;
-        }
-
-        let parsed = parsed_module(db, file);
-
-        let parsed_ref = parsed.load(db);
-        diagnostics.extend(
-            parsed_ref
-                .errors()
-                .iter()
-                .map(|error| Diagnostic::invalid_syntax(file, &error.error, error)),
-        );
-
-        diagnostics.extend(parsed_ref.unsupported_syntax_errors().iter().map(|error| {
-            let mut error = Diagnostic::invalid_syntax(file, error, error);
-            add_inferred_python_version_hint_to_diagnostic(db, &mut error, "parsing syntax");
-            error
-        }));
-
-        {
-            let db = AssertUnwindSafe(db);
-            match catch(&**db, file, || check_types(*db, file)) {
-                Ok(Some(type_check_diagnostics)) => {
-                    diagnostics.extend(type_check_diagnostics.into_iter().cloned());
-                }
-                Ok(None) => {}
-                Err(diagnostic) => diagnostics.push(diagnostic),
+    if let Some(read_error) = source.read_error() {
+        diagnostics.push(
+            IOErrorDiagnostic {
+                file: Some(file),
+                error: read_error.clone().into(),
             }
-        }
-
-        if self
-            .open_fileset(db)
-            .is_none_or(|files| !files.contains(&file))
-        {
-            // Drop the AST now that we are done checking this file. It is not currently open,
-            // so it is unlikely to be accessed again soon. If any queries need to access the AST
-            // from across files, it will be re-parsed.
-            parsed.clear();
-        }
-
-        diagnostics.sort_unstable_by_key(|diagnostic| {
-            diagnostic
-                .primary_span()
-                .and_then(|span| span.range())
-                .unwrap_or_default()
-                .start()
-        });
-
-        diagnostics
+            .to_diagnostic(),
+        );
+        return diagnostics.into_boxed_slice();
     }
+
+    let parsed = parsed_module(db, file);
+
+    let parsed_ref = parsed.load(db);
+    diagnostics.extend(
+        parsed_ref
+            .errors()
+            .iter()
+            .map(|error| Diagnostic::invalid_syntax(file, &error.error, error)),
+    );
+
+    diagnostics.extend(parsed_ref.unsupported_syntax_errors().iter().map(|error| {
+        let mut error = Diagnostic::invalid_syntax(file, error, error);
+        add_inferred_python_version_hint_to_diagnostic(db, &mut error, "parsing syntax");
+        error
+    }));
+
+    {
+        let db = AssertUnwindSafe(db);
+        match catch(&**db, file, || check_types(*db, file)) {
+            Ok(Some(type_check_diagnostics)) => {
+                diagnostics.extend(type_check_diagnostics);
+            }
+            Ok(None) => {}
+            Err(diagnostic) => diagnostics.push(diagnostic),
+        }
+    }
+
+    if db
+        .project()
+        .open_fileset(db)
+        .is_none_or(|files| !files.contains(&file))
+    {
+        // Drop the AST now that we are done checking this file. It is not currently open,
+        // so it is unlikely to be accessed again soon. If any queries need to access the AST
+        // from across files, it will be re-parsed.
+        parsed.clear();
+    }
+
+    diagnostics.sort_unstable_by_key(|diagnostic| {
+        diagnostic
+            .primary_span()
+            .and_then(|span| span.range())
+            .unwrap_or_default()
+            .start()
+    });
+
+    diagnostics.into_boxed_slice()
 }
 
 #[derive(Debug)]
@@ -701,8 +706,8 @@ where
 
 #[cfg(test)]
 mod tests {
-    use crate::Db;
     use crate::ProjectMetadata;
+    use crate::check_file_impl;
     use crate::db::tests::TestDb;
     use ruff_db::Db as _;
     use ruff_db::files::system_path_to_file;
@@ -741,9 +746,8 @@ mod tests {
 
         assert_eq!(source_text(&db, file).as_str(), "");
         assert_eq!(
-            db.project()
-                .check_file_impl(&db, file)
-                .into_iter()
+            check_file_impl(&db, file)
+                .iter()
                 .map(|diagnostic| diagnostic.primary_message().to_string())
                 .collect::<Vec<_>>(),
             vec!["Failed to read file: No such file or directory".to_string()]
@@ -758,9 +762,8 @@ mod tests {
 
         assert_eq!(source_text(&db, file).as_str(), "");
         assert_eq!(
-            db.project()
-                .check_file_impl(&db, file)
-                .into_iter()
+            check_file_impl(&db, file)
+                .iter()
                 .map(|diagnostic| diagnostic.primary_message().to_string())
                 .collect::<Vec<_>>(),
             vec![] as Vec<String>

crates/ty_python_semantic/src/types.rs

@@ -88,8 +88,7 @@ mod definition;
 #[cfg(test)]
 mod property_tests;
 
-#[salsa::tracked(returns(ref), heap_size=get_size2::GetSize::get_heap_size)]
-pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
+pub fn check_types(db: &dyn Db, file: File) -> Vec<Diagnostic> {
     let _span = tracing::trace_span!("check_types", ?file).entered();
 
     tracing::debug!("Checking file '{path}'", path = file.path(db));
@@ -111,7 +110,7 @@ pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
 
     check_suppressions(db, file, &mut diagnostics);
 
-    diagnostics
+    diagnostics.into_vec()
 }
 
 /// Infer the type of a binding.

crates/ty_python_semantic/src/types/diagnostic.rs

@@ -1598,6 +1598,10 @@ impl TypeCheckDiagnostics {
         self.diagnostics.shrink_to_fit();
     }
 
+    pub(crate) fn into_vec(self) -> Vec<Diagnostic> {
+        self.diagnostics
+    }
+
     pub fn iter(&self) -> std::slice::Iter<'_, Diagnostic> {
         self.diagnostics.iter()
     }

crates/ty_python_semantic/src/types/infer.rs

@@ -10035,7 +10035,7 @@ mod tests {
     }
 
     #[track_caller]
-    fn assert_diagnostic_messages(diagnostics: &TypeCheckDiagnostics, expected: &[&str]) {
+    fn assert_diagnostic_messages(diagnostics: &[Diagnostic], expected: &[&str]) {
         let messages: Vec<&str> = diagnostics
             .iter()
             .map(Diagnostic::primary_message)
@@ -10048,7 +10048,7 @@ mod tests {
         let file = system_path_to_file(db, filename).unwrap();
         let diagnostics = check_types(db, file);
 
-        assert_diagnostic_messages(diagnostics, expected);
+        assert_diagnostic_messages(&diagnostics, expected);
     }
 
     #[test]

crates/ty_test/src/lib.rs

@@ -340,7 +340,7 @@ fn run_test(
                 Err(failures) => return Some(failures),
             };
 
-            diagnostics.extend(type_diagnostics.into_iter().cloned());
+            diagnostics.extend(type_diagnostics);
             diagnostics.sort_by(|left, right| {
                 left.rendering_sort_key(db)
                     .cmp(&right.rendering_sort_key(db))