fix(bad-rebase): fixed typos and added test

I had to re-add FromSubstraitFunctionData, so in the process I forgot to
return unique_ptr<FunctionData> instead.

Also re-added missing closing brace.

This also adds a test, but I haven't been able to actually test it.
Additionally, it seems that calling explain is truncating the result, so
I need to figure out how to prevent that from happening in order to
create a proper expected output (and to make the function itself
useful).

src/substrait_extension.cpp

@@ -275,6 +275,7 @@ static unique_ptr<TableRef> FromSubstraitBind(ClientContext &context, TableFunct
 
 static unique_ptr<TableRef> FromSubstraitBindJSON(ClientContext &context, TableFunctionBindInput &input) {
 	return SubstraitBind(context, input, true);
+}
 
 //! Container for TableFnExplainSubstrait to get data from BindFnExplainSubstrait
 struct FromSubstraitFunctionData : public TableFunctionData {
@@ -284,8 +285,8 @@ struct FromSubstraitFunctionData : public TableFunctionData {
 	unique_ptr<Connection> conn;
 };
 
-static unique_ptr<TableRef> BindFnExplainSubstrait(ClientContext &context, TableFunctionBindInput &input
-	                                                 vector<LogicalType> &return_types, vector<string> &names) {
+static unique_ptr<FunctionData> BindFnExplainSubstrait(ClientContext &context, TableFunctionBindInput &input,
+	                                                     vector<LogicalType> &return_types, vector<string> &names) {
 	if (input.inputs[0].IsNull()) {
 		throw BinderException("explain_substrait cannot be called with a NULL parameter");
 	}

test/python/test_substrait_explain.py

@@ -0,0 +1,26 @@
+import pandas as pd
+import duckdb
+
+EXPECTED_RESULT = '''
+┌───────────────┬──────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│  explain_key  │                                            explain_value                                             │
+│    varchar    │                                               varchar                                                │
+├───────────────┼──────────────────────────────────────────────────────────────────────────────────────────────────────┤
+│ physical_plan │ ┌───────────────────────────┐\n│      STREAMING_LIMIT      │\n└─────────────┬─────────────┘\n┌────…  │
+└───────────────┴──────────────────────────────────────────────────────────────────────────────────────────────────────┘
+
+'''
+
+def test_roundtrip_substrait(require):
+    connection = require('substrait')
+    connection.execute('CREATE TABLE integers (i integer)')
+    connection.execute('INSERT INTO integers VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9),(NULL)')
+
+    translate_result = connection.get_substrait('SELECT * FROM integers LIMIT 5')
+    proto_bytes      = translate_result.fetchone()[0]
+
+    expected = pd.Series([EXPECTED_RESULT], name='Explain Plan', dtype='str')
+    actual   = connection.table_function('explain_substrait', proto_bytes).execute()
+
+    pd.testing.assert_series_equal(actual.df()['Explain Plan'], expected)
+