[SR-6945] Error in struct init, saying 'self' used before assignment for the assignment itself

[milseman]

Previous ID	SR-6945
Radar	None
Original Reporter	@milseman
Type	Bug

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: b3efc2af15234adf6e9b4959548a8d2d

is duplicated by:

• SR-15670 'let' property reinitialization checking is flow-insensitive

Issue Description:

When initializing a struct, having a conditional call to another init followed by an early return produces a compilation error about whether the struct was properly initialized.

Reproducer:
https://gist.github.com/milseman/d8360121856f4780bd5172cc94f96251

struct S1 {
  var stored: UInt?

  init(_ x: UInt) {
    if x > 42 {
      self.init(_big: x)
      return
    }
    self.stored = x // <--- error: 'self' used before 'self.init' call or assignment to 'self'
  }

  init(_big x: UInt) {
    self.stored = x
  }
}

struct S2 {
  var stored: UInt?

  init(_ x: UInt) {
    if x > 42 {
      self.init(_big: x)
      return
    }
    self.init(_small: x)
  }

  init(_big x: UInt) {
    self.stored = x
  }

  init(_small x: UInt) {
    self.stored = x
  }
}

S1 has the error, S2 does not.

[gottesmm]

@swift-ci sync

[belkadan]

Workaround: use self = S1(_big: x) instead.

We try to decide up front if a struct initializer is going to be per-field or delegating, but I guess I screwed that check up.

[belkadan]

Not a regression, at least.