[SR-13899] Missing conditional cast fix-it

[dan-zheng]

Previous ID	SR-13899
Radar	None
Original Reporter	@dan-zheng
Type	Bug
Status	Closed
Resolution	Done

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug, DiagnosticsQol, StarterBug, TypeChecker
Assignee	luciano (JIRA)
Priority	Medium

md5: 79f973c3624b69402e948da2cfdd28c7

Issue Description:

let any: Any = 1
if let int = any as Int {
  // ...
}

$ swiftc missing-checked-cast-fixit.swift
missing-conditional-cast-fixit.swift:2:18: error: 'Any' is not convertible to 'Int'; did you mean to use 'as!' to force downcast?
if let int = any as Int {
             ~~~~^~~~~~
                 as!

---

There's only a fix-it for force downcasting (as!). It could also make sense to have one for conditional downcasting (as?), I ran into such a case in practice. Example:

missing-checked-cast-fixit.swift:2:18: error: 'Any' is not convertible to 'Int'; did you mean to use 'as?' to conditionally downcast?
if let int = any as Int {
             ~~~~^~~~~~
                 as?

[dan-zheng]

Done in #34883