fix: check t[k] should not warn unnecessary-if

[EfveZombie]

No description provided.

[gemini-code-assist]

Summary of Changes

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This pull request resolves an issue where the "unnecessary-if" diagnostic incorrectly flagged conditional checks on values retrieved from generic table index access. The underlying problem was that the type inference system did not account for "nil" as a possible return type when accessing a table with a generic key. By explicitly adding "LuaType::Nil" to the inferred type for such operations, the linter now correctly recognizes these "if" checks as necessary, preventing false positive warnings and improving code analysis accuracy.

Highlights

• Diagnostic Fix: Corrected the "unnecessary-if" diagnostic to no longer warn on conditional checks for values obtained from generic table index access, as these values can legitimately be "nil".
• Type Inference: Enhanced type inference for generic table member access (t[k]) to explicitly include "LuaType::Nil" as a possible return type, reflecting Lua's behavior where non-existent keys return "nil".
• Test Coverage: Introduced a new test case (test_table_generic_index_not_unnecessary) to validate that the "unnecessary-if" diagnostic correctly handles generic table index access without false positives.

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Changelog

• crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_if_test.rs
  • Added a new test case "test_table_generic_index_not_unnecessary" to ensure the "unnecessary-if" diagnostic does not trigger for generic table index access.
• crates/emmylua_code_analysis/src/semantic/infer/infer_index/mod.rs
  • Modified "infer_member_by_index_table_generic" to union the inferred type with "LuaType::Nil", allowing for "nil" returns on generic table index access.
• crates/emmylua_code_analysis/src/semantic/member/infer_raw_member.rs
  • Updated "infer_table_generic_raw_member_type" to include "LuaType::Nil" in the returned type for generic table raw member access.

Activity

• The pull request was opened by EfveZombie.
• No further activity has been recorded yet.

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[gemini-code-assist]

Code Review

This pull request correctly fixes an issue where an if check on a value retrieved from a generic table was incorrectly flagged as unnecessary. The changes ensure that the inferred type for a generic table access includes nil, which is the correct behavior in Lua when a key might not exist. The logic in infer_index and infer_raw_member is sound. I've found a small issue in the new test case's assertion which I've commented on.

[gemini-code-assist]

The test name test_table_generic_index_not_unnecessary suggests that this test should pass if the UnnecessaryIf diagnostic is not found. Based on other tests in this file, check_code_for seems to return true when a diagnostic is found. If that's the case, this assertion should be inverted to assert!(!ws.check_code_for(...)) to correctly verify the fix.

Suggested change

	assert!(ws.check_code_for(
	assert!(!ws.check_code_for(

[xuhuanzy]

This change needs a trade-off. I don’t think we need to handle nil here; adding it would introduce a lot of unnecessary annotations.

[lewis6991]

I'd argue this is unnecessary. If you want it not to be then the type of t should be table<string,number?>

[EfveZombie]

Thats what I did, quite counterintuitive to me, but u r right

[EfveZombie]

Current behaviors are same to TypeScript default mode (without noUncheckedIndexedAccess), so I was convinced

Thanks for reviewing /Or2