Re-export modules individually to fix rustdocs (#6757)

* Re-export modules directly to fix rustdocs

* fix

* Add comments

Author: alamb

datafusion/core/src/lib.rs

@@ -430,19 +430,48 @@ pub mod prelude;
 pub mod scalar;
 pub mod variable;
 
-// re-export dependencies from arrow-rs to minimise version maintenance for crate users
+// re-export dependencies from arrow-rs to minimize version maintenance for crate users
 pub use arrow;
 pub use parquet;
 
-// re-export DataFusion crates
-pub use datafusion_common as common;
-pub use datafusion_common::config;
-pub use datafusion_execution;
-pub use datafusion_expr as logical_expr;
-pub use datafusion_optimizer as optimizer;
-pub use datafusion_physical_expr as physical_expr;
-pub use datafusion_row as row;
-pub use datafusion_sql as sql;
+// re-export DataFusion sub-crates at the top level. Use `pub use *`
+// so that the contents of the subcrates appears in rustdocs
+// for details, see https://github.com/apache/arrow-datafusion/issues/6648
+
+/// re-export of [`datafusion_common`] crate
+pub mod common {
+    pub use datafusion_common::*;
+}
+
+// Backwards compatibility
+pub use common::config;
+
+// NB datafusion execution is re-exported in the `execution` module
+
+/// re-export of [`datafusion_expr`] crate
+pub mod logical_expr {
+    pub use datafusion_expr::*;
+}
+
+/// re-export of [`datafusion_optimizer`] crate
+pub mod optimizer {
+    pub use datafusion_optimizer::*;
+}
+
+/// re-export of [`datafusion_physical_expr`] crate
+pub mod physical_expr {
+    pub use datafusion_physical_expr::*;
+}
+
+/// re-export of [`datafusion_row`] crate
+pub mod row {
+    pub use datafusion_row::*;
+}
+
+/// re-export of [`datafusion_sql`] crate
+pub mod sql {
+    pub use datafusion_sql::*;
+}
 
 #[cfg(test)]
 pub mod test;