[Diagnostics] A self argument implicitly passed as an inout parameter is diagnosed as used before initialized

[stzn]

Resolves #55825

When using the self argument that is implicitly passed as an inout parameter without initialization, the compiler generates a "passed by reference before being initialized" diagnostic message.

var test : [String: String]
test["1"] = "1" // variable 'test' passed by reference before being initialized

This error message may be confusing since the "passed by reference" is not explicitly visible in the code.

In this specific case, just "used before being initialized" would be a more understandable diagnostic message.

var test : [String: String]
test["1"] = "1" // variable 'test' used before being initialized

For other uses of inout parameters, the current diagnostic message should remain unchanged, as the additional information about "passed by reference" provides helpful context for developers.

func takes_inout(_ a: inout Int) {}
var a1 : Int
takes_inout(&a1)    //  variable 'a1' passed by reference before being initialized

[AnthonyLatsis]

@swift-ci please smoke test macOS

[omochi]

@swift-ci please smoke test Linux platform
@swift-ci please smoke test Windows platform

[omochi]

@swift-ci please smoke test Linux platform

Excuse me, it seems that only one CI command could be written at a time.

[omochi]

@swift-ci Please smoke test Linux platform

[eeckstein]

lgtm, thanks!