Diagnostics nil check is suppressed by the field value matching the parameter type

[TIMONz1535]

How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

Which OS are you using?

Windows

What is the issue affecting?

Diagnostics/Syntax Checking

Expected Behaviour

Diagnostics nil check does not depend on the field parameter value

---@class A
---@field b string

---@type A?
local a

if a.b == "string1" then end  -- Need check nil
if a.b == "string" then end  -- Need check nil

Actual Behaviour

The string value "string" suppresses the triggering of diagnostics, because of type string of field b.

Reproduction steps

1. Copy the sample code
2. Check the diagnostics a.b == "string" when a should trigger "Need check nil"

Additional Notes

No response

Log File

No response

[idbrii]

Did this break recently? I'm on luals 3.9.3 and I get nil check warnings:

file.lua variable 'a' is never set
file.lua Empty block.
file.lua Need check nil.
file.lua empty if branch
file.lua Empty block.
file.lua Need check nil.
file.lua empty if branch

[tomlau10]

a git bisect yields the following:

5c3086acd08765f9122ed5b7f806e2b2bf3737e3 is the first bad commit
commit 5c3086acd08765f9122ed5b7f806e2b2bf3737e3 (HEAD)
Author: Lewis Russell <[email protected]>
Date:   Sun Sep 22 17:19:12 2024 +0100

    feat: type narrow types with literal fields

 changelog.md                   |  1 +
 script/vm/tracer.lua           | 59 ++++++++++++++++++++++++++++++++++++++++++
 test/type_inference/common.lua | 50 +++++++++++++++++++++++++++++++++++
 3 files changed, 110 insertions(+)

which is #2864 by @lewis6991

---

There seems to be quite a number of regression issues related to that PR now 🤔