Fix panic caused by unknown cursor columns when executing NullRow command. Fixes launchbadge#1249

Author: tyrelr

sqlx-core/src/sqlite/connection/explain.rs

@@ -112,6 +112,50 @@ pub(super) fn explain(
     // Nullable columns
     let mut n = HashMap::<i64, bool>::with_capacity(6);
 
+    let table_block_columns: Vec<(i64, i64, String)> = execute::iter(
+        conn,
+        "SELECT s.rootpage, col.cid as colnum, col.type
+         FROM sqlite_schema s
+         JOIN pragma_table_info(s.name) AS col
+         WHERE s.type = 'table'",
+        None,
+        false,
+    )?
+    .filter_map(|res| res.map(|either| either.right()).transpose())
+    .map(|row| FromRow::from_row(&row?))
+    .collect::<Result<Vec<_>, Error>>()?;
+
+    let index_block_columns: Vec<(i64, i64, String)> = execute::iter(
+        conn,
+        "SELECT s.rootpage, idx.seqno as colnum, col.type
+         FROM sqlite_schema s
+         JOIN pragma_index_info(s.name) AS idx
+         LEFT JOIN pragma_table_info(s.tbl_name) as col
+           ON col.cid = idx.cid
+           WHERE s.type = 'index'",
+        None,
+        false,
+    )?
+    .filter_map(|res| res.map(|either| either.right()).transpose())
+    .map(|row| FromRow::from_row(&row?))
+    .collect::<Result<Vec<_>, Error>>()?;
+
+    let mut cursor_row_info: HashMap<i64, HashMap<i64, DataType>> = HashMap::new();
+    for (block, colnum, datatype) in table_block_columns {
+        let row_info = cursor_row_info.entry(block).or_default();
+        row_info.insert(
+            colnum,
+            datatype.parse().unwrap_or(DataType::Null),
+        );
+    }
+    for (block, colnum, datatype) in index_block_columns {
+        let row_info = cursor_row_info.entry(block).or_default();
+        row_info.insert(
+            colnum,
+            datatype.parse().unwrap_or(DataType::Null),
+        );
+    }
+
     let program: Vec<(i64, String, i64, i64, i64, Vec<u8>)> =
         execute::iter(conn, &format!("EXPLAIN {}", query), None, false)?
             .filter_map(|res| res.map(|either| either.right()).transpose())
@@ -190,7 +234,23 @@ pub(super) fn explain(
 
             OP_OPEN_READ | OP_OPEN_WRITE | OP_OPEN_EPHEMERAL | OP_OPEN_AUTOINDEX => {
                 //Create a new pointer which is referenced by p1
-                p.insert(p1, HashMap::with_capacity(6));
+
+                //Create a new pointer which is referenced by p1, take column metadata from db schema if found
+                if p3 == 0 {
+                    if let Some(table_columns) = cursor_row_info.get(&p2) {
+                        p.insert(
+                            p1,
+                            table_columns
+                                .iter()
+                                .map(|(&colnum, &datatype)| (colnum, datatype))
+                                .collect(),
+                        );
+                    } else {
+                        p.insert(p1, HashMap::with_capacity(6));
+                    }
+                } else {
+                    p.insert(p1, HashMap::with_capacity(6));
+                }
             }
 
             OP_VARIABLE => {