lightning: evaluate all generated columns even if they are virtual

[kennytm]

What problem does this PR solve?

Fix #1404

What is changed and how it works?

Expression indices rely on a virtual generated column, which is not calculated by Lightning (unless depended by a stored generated column). This caused the virtual generated column to contain invalid value and thus invalidate the index.

This PR just calculates all generated columns no matter they are virtual or stored.

Check List

Tests

• Integration test

Code changes

Side effects

• Possible performance regression
  • Tables with only virtual generated columns will experience longer encoding time.

Related changes

• Need to cherry-pick to the release branch
  • release-4.0, 5.0, 5.1 (everywhere that creating an index on virtual generated column is allowed)

Release note

• Expression index and index depending on virtual generated columns are now valid. Previously these indices are broken when importing through Lightning local or importer backend.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• YuJuncen
• glorv

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[glorv]

Why do this PR need to be cherry-picked into 4.0 and 5.0?

[kennytm]

@glorv the following schema works on 4.0 and I believe Lightning before this PR won't populate the b unique index correctly.

create table a(a int primary key, b int as (a + 1) virtual unique);

also, this flag exists on 4.0: https://docs.pingcap.com/zh/tidb/v4.0/tidb-configuration-file#allow-expression-index-%E4%BB%8E-v400-%E7%89%88%E6%9C%AC%E5%BC%80%E5%A7%8B%E5%BC%95%E5%85%A5

[wjhuang2016]

It's removed.

[kennytm]

still needed when cherry-picking.

[glorv]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 031fab4

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #1417.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #1418.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #1419.