fix timestamp with default values comparison

[reedom]

If both sides have identical columns of timestamp with a default value,

CREATE TABLE  (
  column TIMESTAMP NOT NULL DEFAULT(TIMESTAMP '2000-01-01 00:00:00.000000+00:00'),
  …

it panics:

panic: cannot handle unexported field at {spansql.ColumnDef}.Default.(spansql.TimestampLiteral).wall:
	"cloud.google.com/go/spanner/spansql".TimestampLiteral
consider using a custom Comparer; if you control the implementation of type, you can also consider using an Exporter, AllowUnexported, or cmpopts.IgnoreUnexported [recovered]
	panic: cannot handle unexported field at {spansql.ColumnDef}.Default.(spansql.TimestampLiteral).wall:
	"cloud.google.com/go/spanner/spansql".TimestampLiteral
consider using a custom Comparer; if you control the implementation of type, you can also consider using an Exporter, AllowUnexported, or cmpopts.IgnoreUnexported

test that reproduces:

https://github.com/murasaki-bv/hammer/blob/f8af0e9e7cd4b06716aee0fdffe46c21db6aa690/internal/hammer/diff_test.go#L1364-L1381

[daichirata]

@reedom Thank you sincerely for the bug report! I have left some comments, please check them out.

[daichirata]

If I ignore changes here, won't changes to the default value be ignored?

I thought the code would be much better if it could be changed to pass the following test cases.

			from: `
CREATE TABLE Nonces (
  nonce INT64 NOT NULL,
  expires TIMESTAMP NOT NULL DEFAULT(TIMESTAMP '2000-01-01 00:00:00.000000+00:00'),
) PRIMARY KEY(nonce);
`,
			to: `
CREATE TABLE Nonces (
  nonce INT64 NOT NULL,
  expires TIMESTAMP NOT NULL DEFAULT(TIMESTAMP '2000-01-01 12:00:00.000000+00:00'),
) PRIMARY KEY(nonce);
`,
			ignoreAlterDatabase: true,
			expected: []string{
				`ALTER TABLE Nonces ALTER COLUMN expires TIMESTAMP NOT NULL DEFAULT (TIMESTAMP '2000-01-01 12:00:00.000000+00:00')`,
			},

This is an example of an approach, but you might want to make the following comparison here and modify it so that subsequent code will issue an alter statement for changes in the default value.

cmp.Comparer(func(x, y spansql.TimestampLiteral) bool {
	return time.Time(x).Equal(time.Time(y))
}))

[reedom]

My bad…

Ok, I've improved the code.
Could you check it again?

[reedom]

Sorry, it seems I had rerun only a failed test at that time. 🙇
Now the test runs in success locally.

[daichirata]

Thank you for fixing the problem! I appreciate your contribution.