More explicit message on online DDL parsing error

[shlomi-noach]

Description

When submitting an Online DDL request, and the query has a syntax error/typo, Vitess today returns a vague cannot parse statement message.

With this PR, Vitess returns the precise parsing error&position. e.g., right now Vitess does not support GENERATED (notice: fixed by #8117):

mysql> set @@ddl_strategy='online';
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE if not exists t (id bigint unsigned NOT NULL AUTO_INCREMENT, ts datetime(6) DEFAULT NULL, ts_generated int GENERATED ALWAYS AS (ts) VIRTUAL, PRIMARY KEY (id)) ENGINE=InnoDB;
ERROR 1149 (42000): syntax error at position 130 near 'GENERATED'

Related Issue(s)

Fixes #8109

Checklist

• Tests were added or are not required
• Documentation was added or is not required

cc @mavenraven @deepthi @piki @sougou

[shlomi-noach]

make codegen strangely crashes on this branch:

$ make codegen
2021/05/13 12:46:03 saved '/home/shlomi/dev/github/planetscale/vitess-dopple/go/vt/sqlparser/ast_equals.go'
2021/05/13 12:46:03 saved '/home/shlomi/dev/github/planetscale/vitess-dopple/go/vt/sqlparser/ast_clone.go'
2021/05/13 12:46:03 saved '/home/shlomi/dev/github/planetscale/vitess-dopple/go/vt/sqlparser/ast_visit.go'
2021/05/13 12:46:03 saved '/home/shlomi/dev/github/planetscale/vitess-dopple/go/vt/sqlparser/ast_rewrite.go'
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x614764]

goroutine 1 [running]:
go/types.(*Package).Path(...)
	/usr/local/go/src/go/types/package.go:31
main.(*sizegen).getKnownType(0xc00008dc90, 0xc000100b90, 0xc000100b90)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:115 +0x84
main.(*sizegen).sizeStmtForType(0xc00008dc90, 0xc018c43660, 0x6e6b80, 0xc000100b90, 0x0, 0xc0382811d0, 0x1, 0x3)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:385 +0x4b87
main.(*sizegen).sizeImplForStruct(0xc00008dc90, 0xc01de11270, 0xc01ec1e420, 0xc012c29d01, 0x0, 0x6ec401)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:243 +0x371
main.(*sizegen).generateType(0xc00008dc90, 0xc012c779f0, 0xc038247a70, 0xc01ec054a0)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:134 +0xb7
main.(*sizegen).generateType.func1(0x6e6b80, 0xc01ec054a0)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:144 +0xa5
main.findImplementations(0xc012c779a0, 0xc01e0573b0, 0xc00008d7a0)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:168 +0x102
main.(*sizegen).generateType(0xc00008dc90, 0xc012c779f0, 0xc038247a70, 0xc01e057360)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:142 +0x2c9
main.(*sizegen).generateKnownType(0xc00008dc90, 0xc01e057360)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:160 +0x99
main.(*sizegen).finalize(0xc00008dc90, 0xc010195bd0)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:182 +0x9b
main.GenerateSizeHelpers(0xc000104470, 0x1, 0x1, 0xc00012e340, 0x3, 0x4, 0x2b, 0x40dbd8, 0x30)
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:545 +0x45a
main.main()
	/home/shlomi/dev/github/planetscale/vitess-dopple/go/tools/sizegen/sizegen.go:455 +0x230
exit status 2
make: *** [Makefile:145: sizegen] Error 1

[shlomi-noach]

Undid changes to the AST, there is no need to modify AST. codegen is good.

[shlomi-noach]

This PR is good to go and high priority to merge.

[deepthi]

Suggested change

	return vterrors.Errorf(vtrpcpb.Code_ABORTED, "foreign key constraint are not supported in online DDL")
	return vterrors.Errorf(vtrpcpb.Code_ABORTED, "foreign key constraints are not supported in online DDL")

Also, it will be nice to link to the blog post explaining why.

[deepthi]

I have addressed my own review comment.
Now LGTM.