readyset-data: Inferring padding for char columns

We were previously inferring the wrong default value for char columns.
Char columns are padded with spaces to the column length. Instead of
returning an empty string, we now return a string of spaces.

Closes: REA-5699
Closes: #1503

Release-Note-Core: Fixed issue where char columns were not padded with
  spaces when using MRBR and being omitted from the insert.
Change-Id: Icc0842269fa6d9644783888bbc708b3e7776f666
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/9289
Tested-by: Buildkite CI
Reviewed-by: Michael Zink <michael.z@readyset.io>

Author: altmannmarcelo

readyset-data/src/lib.rs

@@ -954,7 +954,13 @@ impl DfValue {
                     // TODO: Fix this to return ByteArray(Vec::new().into())
                     return DfValue::from_str_and_collation("", collation);
                 } else if dftype.is_any_text() {
-                    return DfValue::from_str_and_collation("", collation);
+                    return match dftype {
+                        // For char columns, we return a space repeated to the length of the column
+                        DfType::Char(len, _) => {
+                            DfValue::from_str_and_collation(&" ".repeat(len.into()), collation)
+                        }
+                        _ => DfValue::from_str_and_collation("", collation),
+                    };
                 } else if dftype.is_any_int() || dftype.is_bool() {
                     return DfValue::Int(0);
                 } else if dftype.is_any_float() {

replicators/tests/tests.rs

@@ -4140,3 +4140,62 @@ async fn mysql_minimal_row_based_collation_and_signedness() {
 
     shutdown_tx.shutdown().await;
 }
+
+#[tokio::test(flavor = "multi_thread")]
+#[serial(mysql)]
+#[slow]
+async fn mysql_minimal_row_based_char_padding() {
+    // REA-5699
+    // This test will create a table without PK. The insert will ommit column n, since we are using MRBR it will be deferred to Readyset to fill in the default value.
+    // Then we will update the column and ensure that the update is replicated correctly. Because the table has no PK, this will be a full row delete followed by an insert.
+    // If we did not chose the right default value, the delete will fail.
+    readyset_tracing::init_test_logging();
+    let url = mysql_url();
+    let mut client = DbConnection::connect(&url).await.unwrap();
+
+    client
+        .query("SET binlog_row_image = minimal;")
+        .await
+        .unwrap();
+    client.query("SET sql_mode = '';").await.unwrap();
+    client
+        .query("DROP TABLE IF EXISTS mrbr_char_padding;")
+        .await
+        .unwrap();
+    client
+        .query("CREATE TABLE `mrbr_char_padding` (ID INT, n CHAR(10) NOT NULL);")
+        .await
+        .unwrap();
+
+    let (mut ctx, shutdown_tx) = TestHandle::start_noria(url.to_string(), None)
+        .await
+        .unwrap();
+
+    ctx.controller_rx
+        .as_mut()
+        .unwrap()
+        .snapshot_completed()
+        .await
+        .unwrap();
+
+    client
+        .query("INSERT INTO `mrbr_char_padding` (ID) VALUES (0);")
+        .await
+        .unwrap();
+    client
+        .query("UPDATE `mrbr_char_padding` SET n = 'a' WHERE ID = 0;")
+        .await
+        .unwrap();
+
+    check_results!(
+        ctx,
+        "mrbr_char_padding",
+        "mrbr_char_padding_insert",
+        &[&[
+            DfValue::Int(0),
+            DfValue::from_str_and_collation("a         ", Collation::Citext),
+        ]]
+    );
+
+    shutdown_tx.shutdown().await;
+}