sql/schemachanger: detect secondary and pk index name collisions

Previously, the declarative schema changer did not properly check if
secondary index names and primary index names collided. This meant that
instead of getting a query at statement time, one could be hit at
runtime instead. To address this, this patch checks if either secondary
or primary indexes with the same name exist when creating a new
secondary index.

Fixes: #153702

Release note (bug fix): Addressed a runtime error that could be hit
if a new secondary index had a name collision with a primary index.

Author: fqazi

pkg/sql/logictest/testdata/logic_test/create_index

@@ -693,3 +693,14 @@ tbl_with_collate  CREATE TABLE public.tbl_with_collate (
                   ) WITH (schema_locked = true);
 
 subtest end
+
+
+subtest index_name_conflicts_with_primary_key
+
+statement ok
+CREATE TABLE t_index_name_conflicts_with_primary_key (a INT PRIMARY KEY, b INT);
+
+statement error pgcode 42P07 index with name \"t_index_name_conflicts_with_primary_key_pkey\" already exists
+CREATE INDEX t_index_name_conflicts_with_primary_key_pkey ON t_index_name_conflicts_with_primary_key (a);
+
+subtest end

pkg/sql/schemachanger/scbuild/internal/scbuildstmt/create_index.go

@@ -125,20 +125,34 @@ func CreateIndex(b BuildCtx, n *tree.CreateIndex) {
 			"%q is not a table or materialized view", n.Table.ObjectName))
 	}
 	// Resolve the index name and make sure it doesn't exist yet.
-	{
+	if len(n.Name) > 0 {
 		indexElements := b.ResolveIndex(idxSpec.secondary.TableID, n.Name, ResolveParams{
 			IsExistenceOptional: true,
 			RequiredPrivilege:   privilege.CREATE,
 		})
-		if _, target, sec := scpb.FindSecondaryIndex(indexElements); sec != nil {
+		skipCreation := false
+		indexElements.ForEach(func(_ scpb.Status, target scpb.TargetStatus, e scpb.Element) {
+			switch e.(type) {
+			// Names can conflict on either primary or secondary indexes.
+			case *scpb.PrimaryIndex:
+			case *scpb.SecondaryIndex:
+			default:
+				// No index element that we care about.
+				return
+			}
 			if n.IfNotExists {
+				skipCreation = true
 				return
 			}
 			if target == scpb.ToAbsent {
 				panic(pgerror.Newf(pgcode.ObjectNotInPrerequisiteState,
 					"index %q being dropped, try again later", n.Name.String()))
 			}
 			panic(pgerror.Newf(pgcode.DuplicateRelation, "index with name %q already exists", n.Name))
+		})
+		if skipCreation {
+			return
+
 		}
 	}
 	if _, _, tbl := scpb.FindTable(relationElements); tbl != nil {