feat: Add information_schema (#115)

* feat: Add information_schema

Fixes #98

Cloud will be making requests directly to the database to get info about the
contents of the database, including schemas, tables, and columns.

crates/sqlexec/src/catalog.rs

@@ -1,4 +1,5 @@
 use crate::errors::{internal, Result};
+use crate::information_schema::{InformationSchemaProvider, INFORMATION_SCHEMA};
 use datafusion::catalog::catalog::{CatalogList, CatalogProvider};
 use datafusion::catalog::schema::SchemaProvider;
 use datafusion::datasource::TableProvider;
@@ -30,6 +31,16 @@ impl DatabaseCatalog {
         &self.name
     }
 
+    /// Insert an information schema into this catalog.
+    ///
+    /// Note that this takes an arc as the information schema view needs a
+    /// reference to the catalog since everything is built during query time.
+    pub fn insert_information_schema(self: Arc<Self>) -> Result<()> {
+        let schema = InformationSchemaProvider::new(self.clone());
+        self.insert_schema(INFORMATION_SCHEMA, Arc::new(schema))?;
+        Ok(())
+    }
+
     /// Insert the default "public" schema.
     pub fn insert_default_schema(&self) -> Result<()> {
         let schema = Arc::new(SchemaCatalog::new());

crates/sqlexec/src/engine.rs

@@ -16,8 +16,11 @@ impl Engine {
         let catalog = DatabaseCatalog::new(db_name);
         catalog.insert_default_schema()?;
 
+        let catalog = Arc::new(catalog);
+        DatabaseCatalog::insert_information_schema(catalog.clone())?;
+
         Ok(Engine {
-            catalog: Arc::new(catalog),
+            catalog,
             runtime: Arc::new(runtime),
         })
     }