red-knot[salsa part 2]: Setup semantic DB and Jar (#11837)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/ruff_db/src/source.rs

@@ -0,0 +1,128 @@
+use std::ops::Deref;
+use std::sync::Arc;
+
+use ruff_source_file::LineIndex;
+
+use crate::vfs::VfsFile;
+use crate::Db;
+
+/// Reads the content of file.
+#[salsa::tracked]
+pub fn source_text(db: &dyn Db, file: VfsFile) -> SourceText {
+    let content = file.read(db);
+
+    SourceText {
+        inner: Arc::from(content),
+    }
+}
+
+/// Computes the [`LineIndex`] for `file`.
+#[salsa::tracked]
+pub fn line_index(db: &dyn Db, file: VfsFile) -> LineIndex {
+    let source = source_text(db, file);
+
+    LineIndex::from_source_text(&source)
+}
+
+/// The source text of a [`VfsFile`].
+///
+/// Cheap cloneable in `O(1)`.
+#[derive(Clone, Eq, PartialEq)]
+pub struct SourceText {
+    inner: Arc<str>,
+}
+
+impl SourceText {
+    pub fn as_str(&self) -> &str {
+        &self.inner
+    }
+}
+
+impl Deref for SourceText {
+    type Target = str;
+
+    fn deref(&self) -> &str {
+        self.as_str()
+    }
+}
+
+impl std::fmt::Debug for SourceText {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_tuple("SourceText").field(&self.inner).finish()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use filetime::FileTime;
+    use salsa::EventKind;
+
+    use ruff_source_file::OneIndexed;
+    use ruff_text_size::TextSize;
+
+    use crate::file_system::FileSystemPath;
+    use crate::source::{line_index, source_text};
+    use crate::tests::TestDb;
+    use crate::Db;
+
+    #[test]
+    fn re_runs_query_when_file_revision_changes() {
+        let mut db = TestDb::new();
+        let path = FileSystemPath::new("test.py");
+
+        db.file_system_mut().write_file(path, "x = 10".to_string());
+
+        let file = db.file(path);
+
+        assert_eq!(&*source_text(&db, file), "x = 10");
+
+        db.file_system_mut().write_file(path, "x = 20".to_string());
+        file.set_revision(&mut db).to(FileTime::now().into());
+
+        assert_eq!(&*source_text(&db, file), "x = 20");
+    }
+
+    #[test]
+    fn text_is_cached_if_revision_is_unchanged() {
+        let mut db = TestDb::new();
+        let path = FileSystemPath::new("test.py");
+
+        db.file_system_mut().write_file(path, "x = 10".to_string());
+
+        let file = db.file(path);
+
+        assert_eq!(&*source_text(&db, file), "x = 10");
+
+        // Change the file permission only
+        file.set_permissions(&mut db).to(Some(0o777));
+
+        db.events().lock().unwrap().clear();
+        assert_eq!(&*source_text(&db, file), "x = 10");
+
+        let events = db.events();
+        let events = events.lock().unwrap();
+
+        assert!(!events
+            .iter()
+            .any(|event| matches!(event.kind, EventKind::WillExecute { .. })));
+    }
+
+    #[test]
+    fn line_index_for_source() {
+        let mut db = TestDb::new();
+        let path = FileSystemPath::new("test.py");
+
+        db.file_system_mut()
+            .write_file(path, "x = 10\ny = 20".to_string());
+
+        let file = db.file(path);
+        let index = line_index(&db, file);
+        let text = source_text(&db, file);
+
+        assert_eq!(index.line_count(), 2);
+        assert_eq!(
+            index.line_start(OneIndexed::from_zero_indexed(0), &text),
+            TextSize::new(0)
+        );
+    }
+}