Online DDL shadow table: rename referenced table name in self referencing FK

[shlomi-noach]

Description

Fixes #16204.

In a vitess migration, we programmatically create a shadow table that is a duplicate of the original table, but with a another name. We take care of renaming any constraints as those must be unique across the schema and otherwise copy any foreign key definitions as-is.

However, in the case of a self-referencing foreign key, we must rename the referenced table name to match the shadow table. To illustrate, if we duplicate table t as _vt_vrp_6ace8bcef73211ea87e9f875a4d24e90_20200915120410_, then this statement:

create table t (id int primary key, i int, constraint f foreign key (i) references t (id))

Will now turn into:

create table _vt_vrp_6ace8bcef73211ea87e9f875a4d24e90_20200915120410_ (id int primary key, i int, constraint f foreign key (i) references _vt_vrp_6ace8bcef73211ea87e9f875a4d24e90_20200915120410_ (id))

Backport

Although foreign key support in Online DDL is still considered unsafe, I consider this a bug that is worth backporting, certainly to v20 which we are releasing imminently, but also to previous versions. To clarigy, there' no urgency in backporting this to earlier versions (v20 is the only one that has time constraints as RC2 is scheduled for 3 days from now).

Related Issue(s)

#16204

Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 68.57%. Comparing base (72149e2) to head (d2ad68a).
Report is 3 commits behind head on main.

Files	Patch %	Lines
go/vt/vttablet/onlineddl/executor.go	90.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16205   +/-   ##
=======================================
  Coverage   68.57%   68.57%           
=======================================
  Files        1544     1544           
  Lines      197863   197873   +10     
=======================================
+ Hits       135677   135686    +9     
- Misses      62186    62187    +1     

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[harshit-gangal]

good find.