fix(se): Empty dbgenerated() breaking for Unsupported() types (#4841)

* se: support empty `dbgenerated()` in columns of unsupported types

Empty `dbgenerated()` was fixed for supported types in
#3153 but that PR lacked
the corresponding changes for the unsupported types which this commit
adds.

---------

Co-authored-by: Alexey Orlenko <alex@aqrln.net>

schema-engine/connectors/sql-schema-connector/src/sql_schema_calculator.rs

@@ -414,16 +414,10 @@ fn push_column_for_model_unsupported_scalar_field(
     table_id: sql::TableId,
     ctx: &mut Context<'_>,
 ) {
-    let default = field.default_value().and_then(|def| {
+    let default = field.default_value().map(|def| {
         // This is validated as @default(dbgenerated("...")), we can unwrap.
-        let dbgenerated_contents = unwrap_dbgenerated(def.value());
-        if let Some(value) = dbgenerated_contents {
-            let default =
-                sql::DefaultValue::db_generated(value).with_constraint_name(ctx.flavour.default_constraint_name(def));
-            Some(default)
-        } else {
-            None
-        }
+        sql::DefaultValue::db_generated::<String>(unwrap_dbgenerated(def.value()))
+            .with_constraint_name(ctx.flavour.default_constraint_name(def))
     });
 
     if let Some(default) = default {

schema-engine/sql-migration-tests/tests/migrations/postgres.rs

@@ -735,3 +735,35 @@ fn dbgenerated_on_generated_columns_is_idempotent(api: TestApi) {
 
     api.schema_push(schema).send().assert_green().assert_no_steps();
 }
+
+// https://github.com/prisma/prisma/issues/15654
+#[test_connector(tags(Postgres12), exclude(CockroachDb))]
+fn dbgenerated_on_generated_unsupported_columns_is_idempotent(api: TestApi) {
+    let sql = r#"
+        CREATE TABLE "table" (
+            "id" TEXT NOT NULL,
+            -- NOTE: Modified to make it a PG generated column
+            "hereBeDragons" tsvector GENERATED ALWAYS AS (
+                to_tsvector('english', id::text)
+            ) STORED,
+
+            CONSTRAINT "table_pkey" PRIMARY KEY ("id")
+        );
+    "#;
+
+    api.raw_cmd(sql);
+
+    let schema = r#"
+        datasource db {
+            provider = "postgresql"
+            url = env("TEST_DATABASE_URL")
+        }
+
+        model table {
+            id String @id
+            hereBeDragons Unsupported("tsvector")? @default(dbgenerated())
+        }
+    "#;
+
+    api.schema_push(schema).send().assert_green().assert_no_steps();
+}

schema-engine/sql-migration-tests/tests/single_migration_tests/postgres/empty_dbgenerated.prisma

@@ -3,13 +3,14 @@
 
 datasource testds {
     provider = "postgresql"
-    url = env("TEST_DATABASE_URL")
+    url      = env("TEST_DATABASE_URL")
 }
 
 model table {
-    id String @id
+    id            String @id
     hereBeDragons String @default(dbgenerated())
 }
+
 // Expected Migration:
 // -- CreateTable
 // CREATE TABLE "table" (

schema-engine/sql-migration-tests/tests/single_migration_tests/postgres/empty_unsupported_dbgenerated.prisma

@@ -0,0 +1,21 @@
+// tags=postgres
+// exclude=cockroachdb
+
+datasource testds {
+    provider = "postgresql"
+    url      = env("TEST_DATABASE_URL")
+}
+
+model table {
+    id            String                   @id
+    hereBeDragons Unsupported("tsvector")? @default(dbgenerated())
+}
+
+// Expected Migration:
+// -- CreateTable
+// CREATE TABLE "table" (
+//     "id" TEXT NOT NULL,
+//     "hereBeDragons" tsvector,
+// 
+//     CONSTRAINT "table_pkey" PRIMARY KEY ("id")
+// );

schema-engine/sql-schema-describer/src/lib.rs

@@ -825,8 +825,8 @@ pub enum DefaultKind {
 }
 
 impl DefaultValue {
-    pub fn db_generated(val: impl Into<String>) -> Self {
-        Self::new(DefaultKind::DbGenerated(Some(val.into())))
+    pub fn db_generated<S: Into<String>>(val: impl Into<Option<S>>) -> Self {
+        Self::new(DefaultKind::DbGenerated(val.into().map(Into::into)))
     }
 
     pub fn constraint_name(&self) -> Option<&str> {