spansql: AlterColumn produces invalid SQL when there is an AllowCommitTimestamp OPTION

[oceanful]

Code

package main

import (
  "fmt"

  "cloud.google.com/go/spanner/spansql"
)

func main() {
  allow := true
  stmt := spansql.AlterTable{
    Name: "Tasks",
    Alteration: spansql.AlterColumn{
      Def: spansql.ColumnDef{
        Name: "LastUpdate",
        Type: spansql.Type{Base: spansql.Timestamp},
        AllowCommitTimestamp: &allow,
      },
    },
  }
  fmt.Println(stmt.SQL())
}

Expected behavior

AlterColumn should only alter the column type:

ALTER TABLE Tasks ALTER COLUMN LatestUpdate TIMESTAMP

To support setting options, there should probably be a separate type (maybe something like AlterOptions) that produces:

ALTER TABLE Tasks ALTER COLUMN LatestUpdate SET OPTIONS (allow_commit_timestamp = true)

Actual behavior

The resulting statement is invalid and rejected by spanner:

ALTER TABLE Tasks ALTER COLUMN LatestUpdate TIMESTAMP OPTIONS (allow_commit_timestamp = true);

Error: rpc error: code = InvalidArgument desc = Error parsing Spanner DDL statement: 
ALTER TABLE Tasks ALTER COLUMN LatestUpdateTime TIMESTAMP OPTIONS (allow_commit_timestamp = true) : 
Syntax error on line 1, column ##: Expecting 'EOF' but found 'OPTIONS'

[dsymonds]

The relevant part of https://cloud.google.com/spanner/docs/data-definition-language#ddl_syntax is:

    ALTER [ COLUMN ] column_name { { data_type } [ NOT NULL ] | SET [ options_def ] }

so when we are altering a column, either the data type (or its null-ness) may be changed, or options may be set. Looks like spansql.AlterColumn is too simplistic.

[oceanful]

Thank you!!