From 17b5e71707326a25601bd58b3ad91a745b8a3e10 Mon Sep 17 00:00:00 2001
From: Andrew Lamb <andrew@nerdnetworks.org>
Date: Mon, 3 Feb 2025 12:22:15 -0500
Subject: [PATCH] Fix regression list Type Coercion List with inner type struct
 which has large/view types (#14385)

* Test for coercing inner structs

* Fix but, update tests

* Update tests
---
 .../expr-common/src/type_coercion/binary.rs   | 15 +++---
 datafusion/sqllogictest/test_files/case.slt   | 53 +++++++++++++++++++
 datafusion/sqllogictest/test_files/struct.slt |  8 +--
 3 files changed, 65 insertions(+), 11 deletions(-)

diff --git a/datafusion/expr-common/src/type_coercion/binary.rs b/datafusion/expr-common/src/type_coercion/binary.rs
index ba87a53e5fe8..3be35490a4d0 100644
--- a/datafusion/expr-common/src/type_coercion/binary.rs
+++ b/datafusion/expr-common/src/type_coercion/binary.rs
@@ -566,18 +566,19 @@ fn type_union_resolution_coercion(
                 None
             }
 
-            let types = lhs
+            let coerced_types = lhs
                 .iter()
                 .map(|lhs_field| search_corresponding_coerced_type(lhs_field, rhs))
                 .collect::<Option<Vec<_>>>()?;
 
-            let fields = types
+            // preserve the field name and nullability
+            let orig_fields = std::iter::zip(lhs.iter(), rhs.iter());
+
+            let fields: Vec<FieldRef> = coerced_types
                 .into_iter()
-                .enumerate()
-                .map(|(i, datatype)| {
-                    Arc::new(Field::new(format!("c{i}"), datatype, true))
-                })
-                .collect::<Vec<FieldRef>>();
+                .zip(orig_fields)
+                .map(|(datatype, (lhs, rhs))| coerce_fields(datatype, lhs, rhs))
+                .collect();
             Some(DataType::Struct(fields.into()))
         }
         _ => {
diff --git a/datafusion/sqllogictest/test_files/case.slt b/datafusion/sqllogictest/test_files/case.slt
index 46e9c86c7591..8e470fe988d3 100644
--- a/datafusion/sqllogictest/test_files/case.slt
+++ b/datafusion/sqllogictest/test_files/case.slt
@@ -416,5 +416,58 @@ SELECT
   end
 FROM t;
 
+statement ok
+drop table t
+
+# Fix coercion of lists of structs
+# https://github.com/apache/datafusion/issues/14154
+
+statement ok
+create or replace table t as values
+(
+ 100,                                         -- column1 int (so the case isn't constant folded)
+ [{ 'foo': arrow_cast('baz', 'Utf8View') }],  -- column2 has List of Struct w/ Utf8View
+ [{ 'foo': 'bar' }],                          -- column3 has List of Struct w/ Utf8
+ [{ 'foo': 'blarg' }]                         -- column4 has List of Struct w/ Utf8
+);
+
+# This case forces all branches to be coerced to the same type
+query ?
+SELECT
+  case
+    when column1 > 0 then column2
+    when column1 < 0 then column3
+    else column4
+  end
+FROM t;
+----
+[{foo: baz}]
+
+# different orders of the branches
+query ?
+SELECT
+  case
+    when column1 > 0 then column3 -- NB different order
+    when column1 < 0 then column4
+    else column2
+  end
+FROM t;
+----
+[{foo: bar}]
+
+# different orders of the branches
+query ?
+SELECT
+  case
+    when column1 > 0 then column4 -- NB different order
+    when column1 < 0 then column2
+    else column3
+  end
+FROM t;
+----
+[{foo: blarg}]
+
+
+
 statement ok
 drop table t
diff --git a/datafusion/sqllogictest/test_files/struct.slt b/datafusion/sqllogictest/test_files/struct.slt
index d671798b7d0f..0afe39de1795 100644
--- a/datafusion/sqllogictest/test_files/struct.slt
+++ b/datafusion/sqllogictest/test_files/struct.slt
@@ -459,14 +459,14 @@ create table t as values({r: 'a', c: 1}), ({r: 'b', c: 2.3});
 query ?
 select * from t;
 ----
-{c0: a, c1: 1.0}
-{c0: b, c1: 2.3}
+{r: a, c: 1.0}
+{r: b, c: 2.3}
 
 query T
 select arrow_typeof(column1) from t;
 ----
-Struct([Field { name: "c0", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }, Field { name: "c1", data_type: Float64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }])
-Struct([Field { name: "c0", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }, Field { name: "c1", data_type: Float64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }])
+Struct([Field { name: "r", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }, Field { name: "c", data_type: Float64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }])
+Struct([Field { name: "r", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }, Field { name: "c", data_type: Float64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }])
 
 statement ok
 drop table t;