sql/schemachanger: copy ALTER TABLE .. SET TYPE pre-checks from legac…

…y to DSC

This duplicates various pre-checks we have in the legacy schema
changer's ALTER TABLE .. SET TYPE command to the declarative schema
changer, which uses states from various schema changer elements.

Additionally, it introduces more tests for validation-only type
conversions. These conversions don't require data to be rewritten;
instead, they validate existing rows against the new type. For example,
changing from CHAR(20) to CHAR(10) requires ensuring each row is 10
characters or fewer.

The actual implementation of validation-only type conversions in the DSC
will be handled in a subsequent PR.

Epic: CRDB-25314
Informs: #126516
Release note: None

pkg/sql/alter_column_type.go

@@ -26,23 +26,12 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/cast"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/volatility"
+	"github.com/cockroachdb/cockroach/pkg/sql/sqlerrors"
 	"github.com/cockroachdb/cockroach/pkg/sql/types"
 	"github.com/cockroachdb/cockroach/pkg/util/errorutil/unimplemented"
 	"github.com/cockroachdb/errors"
 )
 
-var colInIndexNotSupportedErr = unimplemented.NewWithIssuef(
-	47636, "ALTER COLUMN TYPE requiring rewrite of on-disk "+
-		"data is currently not supported for columns that are part of an index")
-
-var colOwnsSequenceNotSupportedErr = unimplemented.NewWithIssuef(
-	48244, "ALTER COLUMN TYPE for a column that owns a sequence "+
-		"is currently not supported")
-
-var colWithConstraintNotSupportedErr = unimplemented.NewWithIssuef(
-	48288, "ALTER COLUMN TYPE for a column that has a constraint "+
-		"is currently not supported")
-
 // AlterColTypeInTxnNotSupportedErr is returned when an ALTER COLUMN TYPE
 // is tried in an explicit transaction.
 var AlterColTypeInTxnNotSupportedErr = unimplemented.NewWithIssuef(
@@ -177,34 +166,36 @@ func alterColumnTypeGeneral(
 
 	// Disallow ALTER COLUMN TYPE general for columns that own sequences.
 	if col.NumOwnsSequences() != 0 {
-		return colOwnsSequenceNotSupportedErr
+		return sqlerrors.NewAlterColumnTypeColOwnsSequenceNotSupportedErr()
 	}
 
 	// Disallow ALTER COLUMN TYPE general for columns that have a check
 	// constraint.
 	for _, ck := range tableDesc.EnforcedCheckConstraints() {
 		if ck.CollectReferencedColumnIDs().Contains(col.GetID()) {
-			return colWithConstraintNotSupportedErr
+			return sqlerrors.NewAlterColumnTypeColWithConstraintNotSupportedErr()
 		}
 	}
 
 	// Disallow ALTER COLUMN TYPE general for columns that have a
 	// UNIQUE WITHOUT INDEX constraint.
 	for _, uc := range tableDesc.UniqueConstraintsWithoutIndex() {
 		if uc.CollectKeyColumnIDs().Contains(col.GetID()) {
-			return colWithConstraintNotSupportedErr
+			return sqlerrors.NewAlterColumnTypeColWithConstraintNotSupportedErr()
 		}
 	}
 
 	// Disallow ALTER COLUMN TYPE general for columns that have a foreign key
 	// constraint.
 	for _, fk := range tableDesc.OutboundForeignKeys() {
 		if fk.CollectOriginColumnIDs().Contains(col.GetID()) {
-			return colWithConstraintNotSupportedErr
+			return sqlerrors.NewAlterColumnTypeColWithConstraintNotSupportedErr()
 		}
+	}
+	for _, fk := range tableDesc.InboundForeignKeys() {
 		if fk.GetReferencedTableID() == tableDesc.GetID() &&
 			fk.CollectReferencedColumnIDs().Contains(col.GetID()) {
-			return colWithConstraintNotSupportedErr
+			return sqlerrors.NewAlterColumnTypeColWithConstraintNotSupportedErr()
 		}
 	}
 
@@ -214,7 +205,7 @@ func alterColumnTypeGeneral(
 		if idx.CollectKeyColumnIDs().Contains(col.GetID()) ||
 			idx.CollectKeySuffixColumnIDs().Contains(col.GetID()) ||
 			idx.CollectSecondaryStoredColumnIDs().Contains(col.GetID()) {
-			return colInIndexNotSupportedErr
+			return sqlerrors.NewAlterColumnTypeColInIndexNotSupportedErr()
 		}
 	}