Preserve user-supplied grouping parentheses in boolean expressions

[coderabbitai]

Summary

When formatting SQL, libpgfmt currently drops user-supplied grouping parentheses in WHERE clauses and other boolean expressions. For example, an expression like:

WHERE (sp.cancelled_at IS NULL OR sp.cancelled_at > CURRENT_TIMESTAMP) AND f.feature_name = 'notifications'

is formatted as:

WHERE sp.cancelled_at IS NULL OR sp.cancelled_at > CURRENT_TIMESTAMP AND f.feature_name = 'notifications'

This matches the reference behavior of the Python pgfmt project (which uses pgparse/libpg_query and normalizes away such parentheses at the AST level). However, since libpgfmt uses tree-sitter-postgres (a concrete syntax tree), it is technically feasible to detect and preserve these user-supplied grouping parentheses.

Background

Discussed in PR #1 (#1) at comment #1 (comment).

Raised by @gmr — dropping parentheses is current intentional behavior to match Python pgfmt, with preservation as a planned future improvement.

Goal

Update the expression formatter so that when an OR node (or any lower-precedence boolean operator) is nested inside a higher-precedence boolean context (e.g., AND), the parentheses originally present in the source are emitted in the formatted output to preserve the intended evaluation order and semantics.

Notes

• The tree-sitter-postgres CST retains the parenthesized grouping nodes, making this feasible without external heuristics.
• Care should be taken to only restore parentheses that were present in the original source, not to add new ones based on operator precedence alone.
• Requested by @gmr in PR Add SQL and PL/pgSQL formatting library #1.