Parse @name as a parameter in the Trino dialect

[ravenac95]

What

In the Trino dialect, @name now tokenizes as DAt + name, so the parser builds Expression::Parameter { style: ParameterStyle::At, name: Some("name") }, with the name's case preserved. The generator writes it back as @name.

@name( (a sqlmesh macro function call such as @each(...)) is unchanged: it stays a Var identifier and still round-trips as @NAME(...).

Why

Today every dialect turns @word into a TSQL-style @variable identifier, so in Trino a sqlmesh macro variable like @start_dt parses as a column. Column extraction on multi-table queries then fails with an ambiguous column reference, and lineage reports the macro as unresolved. kuma's query rewriter is about to substitute these macros with a run's time range, which needs them as parameter nodes.

How

• New TokenizerConfig::at_sign_is_parameter (default false). Only TrinoDialect sets it, so every other dialect (TSQL variables, Snowflake @stage, …) tokenizes exactly as before. Note that DuneDialect reuses Trino's tokenizer config, so Dune gets the same behaviour.
• at_word_is_call looks ahead over the word, using the same character set the TSQL identifier scanner consumes, to keep @name( on the old path. Whitespace before ( is not treated as a call (marked ponytail:).
• Side effect: in Trino, FROM @name now goes through the existing stage-reference path instead of producing a table named @name.

Tests

• dialects::trino::tests: SELECT @start_dt FROM t parses to an At parameter named start_dt and round-trips. @some_macro_func('x') still round-trips.
• cargo test -p polyglot-sql --lib passes (1345 tests). cargo fmt --all --check is clean.
• In a full local cargo test, custom_clickhouse_parser failed (missing fixture directory) and so did tpch_transpile_stack (a debug-build stack/hang). Neither involves Trino or @, and CI provides those fixtures.

Consumed by opensource-observer/kuma (OSO-6400), which will re-pin polyglot-sql to this PR's merge commit.

🤖 Generated with Claude Code

https://claude.ai/code/session_019snAi4ViWsw4dALcjcASho

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[linear-code]

OSO-6400

[ravenac95]

Closing this without merging. sqlmesh macro parsing doesn't belong in the polyglot fork, so kuma's query rewriter will normalize Trino @name columns into Parameter { style: At } nodes itself, right after parsing (opensource-observer/kuma#10118). The fork stays at its current rev.

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