storage-cassandra: the migration runner splits a file at a ; inside a comment or a string literal #675

The Cassandra migration runner splits each migration file at every ; and runs each fragment as a statement: sql.split(';') in crates/storage-cassandra/src/migrations.rs, in execute_migration on main and in migration_statements in #638. It doesn't skip comments or string literals, so a ; inside one ends the statement there. @jcshepherd raised this in review on #638, for comments and for string literals.

Running migration_statements from #638's head (370a6b71) with keyspace ks:

• A ; in a comment that follows a statement ends the statement, and the rest of the comment becomes the next statement. For this line:

  CREATE TABLE IF NOT EXISTS b (k int PRIMARY KEY) -- was: ; INSERT INTO settings (key, value) VALUES ('catalog_version', '9.9.9') ;
  

  migration_statements returns CREATE TABLE IF NOT EXISTS ks.b (k int PRIMARY KEY) -- was: and INSERT INTO ks.settings (key, value) VALUES ('catalog_version', '9.9.9'), and the runner runs both. main splits the line the same way and runs both statements too.

• A ; in a string literal cuts the literal in two. INSERT INTO settings (key, value) VALUES ('note', 'a;b'); fails with has a statement that names no table the runner can qualify with a keyspace: b').

• fix(storage-cassandra): qualify migration statements with their keyspace instead of USE #638 skips -- and // comments at the start of a statement before it looks for the table name, but not /* */ comments, so /* header */ CREATE TABLE a (k int PRIMARY KEY); fails with the same error. This one is new in fix(storage-cassandra): qualify migration statements with their keyspace instead of USE #638: main sends the comment through to Cassandra, and CQL allows /* */ comments.

#638 also rejects a fragment that holds only a comment. That catches a ; in a comment between two statements, but not one in a comment that follows a statement.

None of the seven files under crates/storage-cassandra/migrations has a ; in a comment or a string literal, or a /* */ comment, so this affects only migrations added later.

Fix

Split with a scanner that reads the file once and tracks whether it's inside:

• a string literal, in single quotes with '' for a quote inside, or between two $$
• a quoted identifier, in double quotes with "" for a quote inside
• a -- or // comment, which runs to the end of the line
• a /* */ comment, which CQL doesn't nest

The scanner drops comments and splits only at a ; outside all four. A file that ends inside a literal, a quoted identifier or a /* */ comment fails with an error naming the file. Since the scanner drops comments, #638's error for a fragment that holds only a comment is no longer needed. The scanner only tracks quotes and comments, so it doesn't need CQL's grammar.

Tests: the three inputs above, 'x -- y' and 'it''s' in a literal (both stay in the statement), and a $$a;b$$ literal. every_migration_statement_names_the_keyspace (from #638) builds the statements it expects with split(';'), so it has to build them with the scanner instead, and a_fragment_of_only_a_comment_fails_naming_the_file is removed along with the error it tests.