`sqlite-utils transform` breaks DEFAULT string values and STRFTIME()

[kennysong]

Very nice library! Our team found sqlite-utils through @simonw's comment on the "Simple declarative schema migration for SQLite" article, and we were excited to use it, but unfortunately sqlite-utils transform seems to break our DB.

Running sqlite-utils transform to modify a column mangles their DEFAULT values:

• Default string values are wrapped in extra single quotes
• Function expressions such as STRFTIME() are turned into strings!

---

Here are steps to reproduce:

Original database

$ sqlite3 test.db << EOF
CREATE TABLE mytable (
    col1 TEXT DEFAULT 'foo',
    col2 TEXT DEFAULT (STRFTIME('%Y-%m-%d %H:%M:%f', 'NOW'))
)
EOF

$ sqlite3 test.db "SELECT sql FROM sqlite_master WHERE name = 'mytable';"
CREATE TABLE mytable (
    col1 TEXT DEFAULT 'foo',
    col2 TEXT DEFAULT (STRFTIME('%Y-%m-%d %H:%M:%f', 'NOW'))
)

Modified database after sqlite-utils

$ sqlite3 test.db "INSERT INTO mytable DEFAULT VALUES; SELECT * FROM mytable;"
foo|2022-11-02 02:26:58.038

$ sqlite-utils transform test.db mytable --rename col1 renamedcol1

$ sqlite3 test.db "SELECT sql FROM sqlite_master WHERE name = 'mytable';"
CREATE TABLE "mytable" (
   [renamedcol1] TEXT DEFAULT '''foo''',
   [col2] TEXT DEFAULT 'STRFTIME(''%Y-%m-%d %H:%M:%f'', ''NOW'')'
)

$ sqlite3 test.db "INSERT INTO mytable DEFAULT VALUES; SELECT * FROM mytable;"
foo|2022-11-02 02:26:58.038
'foo'|STRFTIME('%Y-%m-%d %H:%M:%f', 'NOW')

(Related: #336)