fix(me): make @db.Float migrations idempotent on MSSQL

We weren't properly handling the implicit precision: we sent FLOAT, got
back FLOAT(53), and interpreted that as different types, but they're the
same.

closes prisma/prisma#14052

migration-engine/connectors/sql-migration-connector/src/sql_schema_differ/sql_schema_differ_flavour/mssql.rs

@@ -1138,9 +1138,13 @@ fn native_type_change_riskyness(previous: MsSqlType, next: MsSqlType) -> Option<
         },
     };
 
-    if previous == next {
-        None
-    } else {
-        Some(cast())
+    match (previous, next) {
+        (p, n) if p == n => None,
+        // https://docs.microsoft.com/en-us/sql/t-sql/data-types/float-and-real-transact-sql?view=sql-server-ver16#syntax
+        (MsSqlType::Float(Some(53)), MsSqlType::Float(None))
+        | (MsSqlType::Float(None), MsSqlType::Float(Some(53)))
+        | (MsSqlType::Float(Some(24)), MsSqlType::Real)
+        | (MsSqlType::Real, MsSqlType::Float(Some(24))) => None,
+        _ => Some(cast()),
     }
 }

migration-engine/migration-engine-tests/tests/migrations/mssql.rs

@@ -302,3 +302,51 @@ fn bigint_defaults_work(api: TestApi) {
     api.schema_push(schema).send().assert_green();
     api.schema_push(schema).send().assert_green().assert_no_steps();
 }
+
+#[test_connector(tags(Mssql))]
+fn float_columns(api: TestApi) {
+    let schema = r#"
+        datasource mypg {
+            provider = "sqlserver"
+            url = env("TEST_DATABASE_URL")
+        }
+
+        model foo {
+          id  String @id
+          bar Float @mypg.Float @default(0.90001)
+          baz Float? @mypg.Float
+          qux Float? @mypg.Real
+        }
+    "#;
+    let sql = expect![[r#"
+        BEGIN TRY
+
+        BEGIN TRAN;
+
+        -- CreateTable
+        CREATE TABLE [float_columns].[foo] (
+            [id] NVARCHAR(1000) NOT NULL,
+            [bar] FLOAT NOT NULL CONSTRAINT [foo_bar_df] DEFAULT 0.90001,
+            [baz] FLOAT,
+            [qux] REAL,
+            CONSTRAINT [foo_pkey] PRIMARY KEY CLUSTERED ([id])
+        );
+
+        COMMIT TRAN;
+
+        END TRY
+        BEGIN CATCH
+
+        IF @@TRANCOUNT > 0
+        BEGIN
+            ROLLBACK TRAN;
+        END;
+        THROW
+
+        END CATCH
+    "#]];
+    api.expect_sql_for_schema(schema, &sql);
+
+    api.schema_push(schema).send().assert_green();
+    api.schema_push(schema).send().assert_green().assert_no_steps();
+}