[BUG] Wrong statement when using `generated always as`

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
52/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
go, postgres
Domain
databases

Research direction

Start by reproducing the issue with pg-schema-diff apply using the generated column definition and the provided Postgres versions. Trace how the schema diff represents generated expressions and verify that the migration plan preserves GENERATED ALWAYS AS and applies successfully without producing a DEFAULT expression.

Written by the indexing model from the issue text.

Description

bug
Describe the bug

When I pg-schema-diff apply after adding this column:

search_vector tsvector generated always as (
  to_tsvector('simple', title || ' ' || coalesce(artist, ''))
) stored

I get the following error:

Error: generating plan: validating migration plan: running migration plan: executing migration statement: {ALTER TABLE "public"."tabs" ADD COLUMN "search_vector" tsvector DEFAULT to_tsvector('simple'::regconfig, ((title || ' '::text) || COALESCE(artist, ''::text))) 3s 3s []}: ERROR: cannot use column reference in DEFAULT expression (SQLSTATE 0A000) 
diff.Plan{
    Statements: {
        {
            DDL:         "ALTER TABLE \"public\".\"tabs\" ADD COLUMN \"search_vector\" tsvector DEFAULT to_tsvector('simple'::regconfig, ((title || ' '::text) || COALESCE(artist, ''::text)))",
            Timeout:     3000000000,
            LockTimeout: 3000000000,
            Hazards:     nil,
        },
    },
    CurrentSchemaHash: "22b8e78772d29e38",
}

It seems that pg-schema-diff is changing the ...generated always as ... to ...default...

Expected behavior

Use generated always as.

Context

pg-schema-diff version: Version=v0.9.0
Postgres version: 17
pg-schema-diff apply --dsn url --schema-dir db/

Dominant language
Go
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