From f2728e230217da323baefec492106326c6fcdac6 Mon Sep 17 00:00:00 2001
From: Fantix King <fantix.king@gmail.com>
Date: Thu, 13 Feb 2025 11:46:10 -0500
Subject: [PATCH] add back compiler start transaction modifiers

---
 edb/server/compiler/compiler.py | 46 +++++++++++++++++++++++----------
 1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/edb/server/compiler/compiler.py b/edb/server/compiler/compiler.py
index 23ba0f59b9d3..ea9dd61eb4ba 100644
--- a/edb/server/compiler/compiler.py
+++ b/edb/server/compiler/compiler.py
@@ -66,6 +66,7 @@
 from edb.edgeql import qltypes
 
 from edb.ir import staeval as ireval
+from edb.ir import statypes
 from edb.ir import ast as irast
 
 from edb.schema import ddl as s_ddl
@@ -2152,22 +2153,39 @@ def _compile_ql_transaction(
 
         ctx.state.start_tx()
 
-        sqls = 'START TRANSACTION'
+        # Compute the effective isolation level
+        iso_config: statypes.TransactionIsolation = _get_config_val(
+            ctx, "default_transaction_isolation"
+        )
+        default_iso = iso_config.to_qltypes()
         iso = ql.isolation
-        if iso is not None:
-            if (
-                iso is not qltypes.TransactionIsolationLevel.SERIALIZABLE
-                and ql.access is not qltypes.TransactionAccessMode.READ_ONLY
-            ):
-                raise errors.TransactionError(
-                    f"{iso.value} transaction isolation level is only "
-                    "supported in read-only transactions",
-                    span=ql.span,
-                    hint=f"specify READ ONLY access mode",
+        if iso is None:
+            iso = default_iso
+
+        # Compute the effective access mode
+        access = ql.access
+        if access is None:
+            if default_iso is qltypes.TransactionIsolationLevel.SERIALIZABLE:
+                access_mode: statypes.TransactionAccessMode = _get_config_val(
+                    ctx, "default_transaction_access_mode"
                 )
-            sqls += f' ISOLATION LEVEL {iso.value}'
-        if ql.access is not None:
-            sqls += f' {ql.access.value}'
+                access = access_mode.to_qltypes()
+            else:
+                access = qltypes.TransactionAccessMode.READ_ONLY
+
+        # Guard against unsupported isolation + access combinations
+        if (
+            iso is not qltypes.TransactionIsolationLevel.SERIALIZABLE
+            and access is not qltypes.TransactionAccessMode.READ_ONLY
+        ):
+            raise errors.TransactionError(
+                f"{iso.value} transaction isolation level is only "
+                "supported in read-only transactions",
+                span=ql.span,
+                hint=f"specify READ ONLY access mode",
+            )
+
+        sqls = f'START TRANSACTION ISOLATION LEVEL {iso.value} {access.value}'
         if ql.deferrable is not None:
             sqls += f' {ql.deferrable.value}'
         sqls += ';'