[SR-7445] Call Expressions Need Better Assignment Diagnostics

[CodaFi]

Previous ID	SR-7445
Radar	None
Original Reporter	@CodaFi
Type	Improvement
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Improvement, DiagnosticsQoI, StarterBug
Assignee	@AnthonyLatsis
Priority	Medium

md5: d9d262db67912b2400f15a80852abcb8

Issue Description:

Call expressions are not handled in the walker at ConstraintSystem::diagnoseAssignmentFailure in CSDiag.cpp. A new diagnostic needs to be added to DiagnosticsSema.def and it needs to be invoked by that function. It would also be great to clean up the existing diagnostics by giving them better messages.

print(1) = () // error: cannot assign to value: function call returns immutable value 

[AnthonyLatsis]

@CodaFi Would you like a different diag for function calls? This one seems alright, or rather, I can't really think of a more appropriate message.

Maybe expression not assignable: ... . Any ideas?

[AnthonyLatsis]

PR(merged) – #16179

Also added highlighting for assignments to literals in complex expressions and updated the diagnosing paths to display cannot assign to value for methods (was cannot assign to property)