memory database with JSON column cannot be updated

[firelizzard18]

func TestJsonUpdate(t *testing.T) {
	table := memory.NewTable(t.Name(), sql.Schema{
		{Name: "json", Type: sql.JSON, Nullable: false, Source: t.Name()},
	})

	old := sql.NewRow(sql.JSONDocument{Val: []string{"foo", "bar"}})
	new := sql.NewRow(sql.JSONDocument{Val: []string{"foo"}})

	ctx := sql.NewEmptyContext()
	table.Insert(ctx, old)

	up := table.Updater(ctx)
	up.Update(ctx, old, new)
}

results in

--- FAIL: TestJsonUpdate (0.00s)
panic: runtime error: comparing uncomparable type []string [recovered]
        panic: runtime error: comparing uncomparable type []string

goroutine 22 [running]:
testing.tRunner.func1.2(0x16996e0, 0xc000289e70)
        GOPATH/src/testing/testing.go:1144 +0x332
testing.tRunner.func1(0xc000102a80)
        GOPATH/src/testing/testing.go:1147 +0x4b6
panic(0x16996e0, 0xc000289e70)
        GOPATH/src/runtime/panic.go:965 +0x1b9
github.com/dolthub/go-mysql-server/memory.(*tableEditor).Update(0xc000133f18, 0xc000204ab0, 0xc000289d90, 0x1, 0x1, 0xc000289dc0, 0x1, 0x1, 0x105a2a5, 0x10740c0)
        CODE/go-mysql-server/memory/table.go:621 +0x275
github.com/dolthub/go-mysql-server/memory_test.TestJsonUpdate(0xc000102a80)
        CODE/go-mysql-server/memory/regression_test.go:36 +0x405
testing.tRunner(0xc000102a80, 0x178a6a0)
        GOPATH/src/testing/testing.go:1194 +0xef
created by testing.(*T).Run
        GOPATH/src/testing/testing.go:1239 +0x2b3
FAIL    github.com/dolthub/go-mysql-server/memory       0.019s
FAIL

[firelizzard18]

Also true for delete

[andy-wm-arthur]

@firelizzard18 thanks for the bug! I'll take a look.

At first glance, it might be cause by []string{ "foo", "bar"} vs []interface{"foo", "bar"}.

[firelizzard18]

@andrew-wm-arthur The issue is that arrays are not comparable:

A comparison of two interface values with identical dynamic types causes a run-time panic if values of that type are not comparable. This behavior applies not only to direct interface value comparisons but also when comparing arrays of interface values or structs with interface-valued fields.

Slice, map, and function values are not comparable. However, as a special case, a slice, map, or function value may be compared to the predeclared identifier nil. Comparison of pointer, channel, and interface values to nil is also allowed and follows from the general rules above.

(*memory.Table).Insert is a bit weird, in that it circumvents the processing/normalization of values done by the sql package when an INSERT is executed. _example/main.go inserts values directly, without being wrapped in a sql.JSONDocument. However, even if the insert is done via SQL, or if you wrap the value with a JSONDocument, it still breaks, because then you're comparing two JSONDocuments that point to arrays, and types that contain an incomparable are themselves incomparable.

The solution is to modify (*memory.tableEditor).Update and .Delete: when comparing two rows, if a given column is sqltypes.TypeJSON, use sql.Type.Compare(a, b) == 0 instead of ==. I submitted a fix as part of #356, since the bug was breaking my tests.