fix: bind an empty JSON array as the quoted '{}' literal (#86)

[aesslinger]

Summary

• json_array_to_pg_literal had no empty-array special case, so an empty JSON array [] produced ARRAY[] (an ARRAY constructor with no elements), which PostgreSQL rejects in many contexts — a syntax error, or "cannot determine type of empty array" — since the server can't infer an element type from zero elements.
• The builtin driver special-cases this to '{}', the canonical PostgreSQL empty-array literal the server always accepts regardless of context.

Note on the fix value: the issue's suggested code snippet used a bare, unquoted {}, but that's itself a syntax error on its own (confirmed live: syntax error at or near "{"). I checked the builtin's actual current source (src-tauri/src/drivers/postgres/helpers.rs::json_array_to_pg_literal) and its git history — it has always quoted this as '{}', going back to when the function was first introduced. Matched that exactly (and verified the quoted form works live) rather than the issue's snippet.

Both call sites that reach json_array_to_pg_literal — bind_pg_value's native Value::Array arm, and bind_pg_string's inline "[...]"-embedded-in-a-string parse — share this one function, so the fix covers both without duplication.

Fixes #86.

Test plan

• TDD: added 3 new unit tests to binding_tests.rs (native empty array, empty array embedded in a string, nested empty array). Confirmed the first two fail against the pre-fix code (ARRAY[] vs expected '{}') before the fix, pass after.
• cargo test --lib — 312 passed
• cargo clippy --all-targets -- -D warnings — clean
• cargo fmt --all -- --check — clean
• Live end-to-end verification against a real PostgreSQL instance:
  • The issue's exact repro (INSERT of {"ids": []} into an int[] column) now succeeds and round-trips as an empty array instead of erroring
  • A non-empty array still binds unchanged (no regression)
  • The string-embedded "[]" path binds identically to the native array path
  • Confirmed a pre-existing, shared limitation carries over unchanged from the builtin: a uniform nested empty array like [[],[]] still hits PostgreSQL's own type-inference gap for ARRAY['{}', '{}'] (each '{}' looks like text to the parser) — reproduced the same error against bare psql using the builtin's exact algorithm, confirming this is inherited behavior, not introduced by this fix, and out of scope for Empty JSON array binds as ARRAY[] instead of '{}' (server errors in many array-column contexts) #86

[github-actions]

Version suggestion

Based on this PR's title (fix) and the prerelease:rc label:

Current	1.0.0-rc.3
Suggested next tag	v1.0.0-rc.4

This is informational only — no tag or release is created automatically yet.

[github-actions]

Version suggestion

Based on this PR's title (fix) and the prerelease:rc label:

Current	1.0.0-rc.3
Suggested next tag	v1.0.0-rc.4

This is informational only — no tag or release is created automatically yet.