fix(builder): main ref removal

table/metadata.go

@@ -623,7 +623,8 @@ func (b *MetadataBuilder) RemoveSnapshotRef(name string) (*MetadataBuilder, erro
 	}
 
 	if name == MainBranch {
-		return nil, errors.New("cannot remove main branch's snapshot ref")
+		b.currentSnapshotID = nil
+		b.snapshotLog = b.snapshotLog[:0]
 	}
 
 	delete(b.refs, name)
@@ -1037,6 +1038,10 @@ func (c *commonMetadata) preValidate() {
 		c.CurrentSnapshotID = nil
 	}
 
+	if c.SnapshotRefs == nil {
+		c.SnapshotRefs = map[string]SnapshotRef{}
+	}
+
 	if c.CurrentSnapshotID != nil {
 		if _, ok := c.SnapshotRefs[MainBranch]; !ok {
 			c.SnapshotRefs[MainBranch] = SnapshotRef{

table/metadata_builder_internal_test.go

@@ -194,3 +194,22 @@ func TestCannotAddDuplicateSnapshotID(t *testing.T) {
 	_, err = builder.AddSnapshot(&snapshot)
 	require.ErrorContains(t, err, "can't add snapshot with id 2, already exists")
 }
+
+func TestRemoveMainSnapshotRef(t *testing.T) {
+	meta, err := getTestTableMetadata("TableMetadataV2Valid.json")
+	require.NoError(t, err)
+	require.NotNil(t, meta)
+	require.NotNil(t, meta.CurrentSnapshot())
+	builder, err := MetadataBuilderFromBase(meta)
+	require.NoError(t, err)
+	require.NotNil(t, builder.currentSnapshotID)
+	if _, ok := builder.refs[MainBranch]; !ok {
+		t.Fatal("expected main branch to exist")
+	}
+	_, err = builder.RemoveSnapshotRef(MainBranch)
+	require.NoError(t, err)
+	require.Nil(t, builder.currentSnapshotID)
+	meta, err = builder.Build()
+	require.NoError(t, err)
+	require.NotNil(t, meta)
+}

table/metadata_internal_test.go

@@ -19,6 +19,8 @@ package table
 
 import (
 	"encoding/json"
+	"os"
+	"path"
 	"slices"
 	"testing"
 
@@ -949,3 +951,16 @@ func TestMetadataV2Validation(t *testing.T) {
 	// Test case 3: Verify LastColumnId maintains 0 when explicitly set
 	require.NoError(t, meta3.UnmarshalJSON([]byte(zeroColumnID)))
 }
+
+func getTestTableMetadata(fileName string) (Metadata, error) {
+	fCont, err := os.ReadFile(path.Join("testdata", fileName))
+	if err != nil {
+		return nil, err
+	}
+	meta, err := ParseMetadataBytes(fCont)
+	if err != nil {
+		return nil, err
+	}
+
+	return meta, nil
+}

table/testdata/TableMetadataV2Valid.json

@@ -0,0 +1,122 @@
+{
+  "format-version": 2,
+  "table-uuid": "9c12d441-03fe-4693-9a96-a0705ddf69c1",
+  "location": "s3://bucket/test/location",
+  "last-sequence-number": 34,
+  "last-updated-ms": 1602638573590,
+  "last-column-id": 3,
+  "current-schema-id": 1,
+  "schemas": [
+    {
+      "type": "struct",
+      "schema-id": 0,
+      "fields": [
+        {
+          "id": 1,
+          "name": "x",
+          "required": true,
+          "type": "long"
+        }
+      ]
+    },
+    {
+      "type": "struct",
+      "schema-id": 1,
+      "identifier-field-ids": [
+        1,
+        2
+      ],
+      "fields": [
+        {
+          "id": 1,
+          "name": "x",
+          "required": true,
+          "type": "long"
+        },
+        {
+          "id": 2,
+          "name": "y",
+          "required": true,
+          "type": "long",
+          "doc": "comment"
+        },
+        {
+          "id": 3,
+          "name": "z",
+          "required": true,
+          "type": "long"
+        }
+      ]
+    }
+  ],
+  "default-spec-id": 0,
+  "partition-specs": [
+    {
+      "spec-id": 0,
+      "fields": [
+        {
+          "name": "x",
+          "transform": "identity",
+          "source-id": 1,
+          "field-id": 1000
+        }
+      ]
+    }
+  ],
+  "last-partition-id": 1000,
+  "default-sort-order-id": 3,
+  "sort-orders": [
+    {
+      "order-id": 3,
+      "fields": [
+        {
+          "transform": "identity",
+          "source-id": 2,
+          "direction": "asc",
+          "null-order": "nulls-first"
+        },
+        {
+          "transform": "bucket[4]",
+          "source-id": 3,
+          "direction": "desc",
+          "null-order": "nulls-last"
+        }
+      ]
+    }
+  ],
+  "properties": {},
+  "current-snapshot-id": 3055729675574597004,
+  "snapshots": [
+    {
+      "snapshot-id": 3051729675574597004,
+      "timestamp-ms": 1515100955770,
+      "sequence-number": 0,
+      "summary": {
+        "operation": "append"
+      },
+      "manifest-list": "s3://a/b/1.avro"
+    },
+    {
+      "snapshot-id": 3055729675574597004,
+      "parent-snapshot-id": 3051729675574597004,
+      "timestamp-ms": 1555100955770,
+      "sequence-number": 1,
+      "summary": {
+        "operation": "append"
+      },
+      "manifest-list": "s3://a/b/2.avro",
+      "schema-id": 1
+    }
+  ],
+  "snapshot-log": [
+    {
+      "snapshot-id": 3051729675574597004,
+      "timestamp-ms": 1515100955770
+    },
+    {
+      "snapshot-id": 3055729675574597004,
+      "timestamp-ms": 1555100955770
+    }
+  ],
+  "metadata-log": []
+}