Test synthetic key with a single unary keyless relation

Cover the case where a synthetic key feeds a single relation that has no
value columns — i.e. the relation holds just the (synthetic) key. Adds the
`relations_synthetic_key_unary` round-trip fixture and a matching parser unit
test asserting synthetic_key is set, keys is empty, and the sole target has no
value columns.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: hbarthels

sdks/python/tests/test_parser.py

@@ -127,6 +127,21 @@ def test_synthetic_key_marker():
     assert [c.name for c in relations.keys] == ["id"]
 
 
+def test_synthetic_key_with_unary_keyless_relation():
+    # A synthetic key with a single relation that has no value columns: the
+    # relation holds just the (synthetic) key.
+    fragment = (
+        '(fragment :f (csv_data (csv_locator (paths "x.csv")) (csv_config {}) '
+        "(relations (keys synthetic) (relation :keys)) "
+        '(asof "2025-01-01T00:00:00Z")))'
+    )
+    relations = _relations_of(fragment)
+    assert relations.synthetic_key is True
+    assert list(relations.keys) == []
+    assert len(relations.plain.targets) == 1
+    assert list(relations.plain.targets[0].values) == []
+
+
 def test_synthetic_key_rejects_unknown_marker():
     # Only the `synthetic` marker is accepted; anything else is a hard error.
     with pytest.raises(ParseError):

tests/bin/relations_synthetic_key_unary.bin

@@ -0,0 +1,13 @@
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tests/lqp/relations_synthetic_key_unary.lqp

@@ -0,0 +1,18 @@
+(transaction
+  (epoch
+    (writes
+      (define
+        (fragment :f1
+          ;; Generalized CSV loading with a synthetic (loader-generated) key and a single
+          ;; unary relation that carries no value columns — the relation holds just the key.
+          (csv_data
+            (csv_locator
+              (paths "s3://bucket/keys.csv"))
+            (csv_config {})
+            (relations
+              (keys synthetic)
+              (relation :keys))
+            (asof "2025-06-01T00:00:00Z")))))
+
+    (reads
+      (output :keys :keys))))

tests/pretty/relations_synthetic_key_unary.lqp

@@ -0,0 +1,22 @@
+(transaction
+  (configure { :ivm.maintenance_level "off" :semantics_version 0})
+  (epoch
+    (writes
+      (define
+        (fragment
+          :f1
+          (csv_data
+            (csv_locator (paths "s3://bucket/keys.csv"))
+            (csv_config
+              {
+               :csv_compression ""
+               :csv_decimal_separator "."
+               :csv_delimiter ","
+               :csv_encoding "utf-8"
+               :csv_escapechar "\""
+               :csv_header_row 1i32
+               :csv_quotechar "\""
+               :csv_skip 0})
+            (relations (keys synthetic) (relation :keys))
+            (asof "2025-06-01T00:00:00Z")))))
+    (reads (output :keys :keys))))

tests/pretty_debug/relations_synthetic_key_unary.lqp

@@ -0,0 +1,27 @@
+(transaction
+  (configure { :ivm.maintenance_level "off" :semantics_version 0})
+  (epoch
+    (writes
+      (define
+        (fragment
+          :f1
+          (csv_data
+            (csv_locator (paths "s3://bucket/keys.csv"))
+            (csv_config
+              {
+               :csv_compression ""
+               :csv_decimal_separator "."
+               :csv_delimiter ","
+               :csv_encoding "utf-8"
+               :csv_escapechar "\""
+               :csv_header_row 1i32
+               :csv_quotechar "\""
+               :csv_skip 0})
+            (relations (keys synthetic) (relation 0xd382b3db273cff4344b6d39d5379c923))
+            (asof "2025-06-01T00:00:00Z")))))
+    (reads (output :keys 0xd382b3db273cff4344b6d39d5379c923))))
+
+;; Debug information
+;; -----------------------
+;; Original names
+;; 	 ID `0xd382b3db273cff4344b6d39d5379c923` -> `keys`