(arrow) branch main updated: GH-44714: [C++] Keep field metadata for keys and values when importing a map type via the C data interface (#44715)

[apitrou]

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The following commit(s) were added to refs/heads/main by this push:
     new 152e878a2e GH-44714: [C++] Keep field metadata for keys and values 
when importing a map type via the C data interface (#44715)
152e878a2e is described below

commit 152e878a2e79877ec461f96cefc97663f0bc581f
Author: Dewey Dunnington <de...@voltrondata.com>
AuthorDate: Mon Nov 18 14:03:48 2024 +0000

    GH-44714: [C++] Keep field metadata for keys and values when importing a 
map type via the C data interface (#44715)
    
    ### Rationale for this change
    
    Import of a map type from the C data interface drops field metadata 
(including extension type information) which does not happen when importing a 
map type from IPC or a list of structs. This affects the ability to roundtrip 
data through pyarrow/Arrow C++ if extension types are not registered.
    
    ### What changes are included in this PR?
    
    The mechanism to import the map type was changed to align with the method 
used for IPC import.
    
    ### Are these changes tested?
    
    Yes.
    
    ### Are there any user-facing changes?
    
    The current behaviour was surprising/inconsistent, so I think this PR 
brings it in more line with the current expectation/documentation.
    * GitHub Issue: #44714
    
    Authored-by: Dewey Dunnington <de...@voltrondata.com>
    Signed-off-by: Antoine Pitrou <anto...@python.org>
---
 cpp/src/arrow/c/bridge.cc      | 8 ++++----
 cpp/src/arrow/c/bridge_test.cc | 4 ++++
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/cpp/src/arrow/c/bridge.cc b/cpp/src/arrow/c/bridge.cc
index f848b34115..6b30802c78 100644
--- a/cpp/src/arrow/c/bridge.cc
+++ b/cpp/src/arrow/c/bridge.cc
@@ -1310,13 +1310,13 @@ struct SchemaImporter {
     }
 
     bool keys_sorted = (c_struct_->flags & ARROW_FLAG_MAP_KEYS_SORTED);
-    bool values_nullable = value_type->field(1)->nullable();
+
     // Some implementations of Arrow (such as Rust) use a non-standard field 
name
     // for key ("keys") and value ("values") fields. For simplicity, we 
override
     // them on import.
-    auto values_field =
-        ::arrow::field("value", value_type->field(1)->type(), values_nullable);
-    type_ = map(value_type->field(0)->type(), values_field, keys_sorted);
+    type_ =
+        std::make_shared<MapType>(value_type->field(0)->WithName("key"),
+                                  value_type->field(1)->WithName("value"), 
keys_sorted);
     return Status::OK();
   }
 
diff --git a/cpp/src/arrow/c/bridge_test.cc b/cpp/src/arrow/c/bridge_test.cc
index bc60b587cf..75fadc7c02 100644
--- a/cpp/src/arrow/c/bridge_test.cc
+++ b/cpp/src/arrow/c/bridge_test.cc
@@ -3769,6 +3769,10 @@ TEST_F(TestSchemaRoundtrip, RegisteredExtension) {
 TEST_F(TestSchemaRoundtrip, Map) {
   TestWithTypeFactory([&]() { return map(utf8(), int32()); });
   TestWithTypeFactory([&]() { return map(utf8(), field("value", int32(), 
false)); });
+  TestWithTypeFactory([&]() {
+    return map(utf8(), field("value", int32(), false,
+                             KeyValueMetadata::Make({"meta key"}, {"meta 
value"})));
+  });
   // Field names are brought in line with the spec on import.
   TestWithTypeFactory(
       [&]() {