feat: TSQL IDENTITY, named UNIQUE/FOREIGN KEY constraints and trailing comma

[jtrv]

SQL Server CREATE TABLE scripts hit three gaps. Each one produces an ERROR node that swallows the rest of the table definition:

CREATE TABLE dbo.assembly (
  id int IDENTITY (1, 1) NOT NULL,                        -- IDENTITY column constraint
  customer_id int NOT NULL,
  CONSTRAINT pk_assembly PRIMARY KEY (id),
  CONSTRAINT fk_assembly_customer FOREIGN KEY (customer_id)
    REFERENCES dbo.customer(id),                          -- named FOREIGN KEY
  CONSTRAINT uq_assembly UNIQUE (customer_id),            -- named UNIQUE
);                                                        -- trailing comma

Changes:

• keyword_identity: a new column constraint, IDENTITY with an optional (seed, increment). The two values are exposed as seed and increment fields. Also added to highlights.scm next to keyword_auto_increment.
• _constraint_literal: after CONSTRAINT <name> it now accepts _key_constraint (UNIQUE / FOREIGN KEY … REFERENCES) as well as PRIMARY KEY and CHECK.
• column_definitions: accepts an optional trailing , before ). The comma after the last constraint left the parser unable to tell whether another constraint or the closing ) comes next, so [$.constraints] is added to conflicts to let it try both.

The new corpus test is in test/corpus/create.txt. All existing tests still pass. Unchanged:

• GENERATED ALWAYS AS IDENTITY produces the same tree as before.
• identity still works as a column name.

🤖 Generated with Claude Code