Fix Bootstrap: diffing

etcwilde · etcwilde · commit 0a409130d3f0 · 2025-09-19T16:51:06.000-07:00
The pass that tracks which control-flow positions are unreachable after infinite loops was migrated to pure Swift in PR #79186. As a result, the C++-only compiler used to bootstrap is unable to determine that the code-location after loops is unreachable. Placing a fatalError after the infinite while loop. Fixes: rdar://160956325
diff --git a/stdlib/public/core/Diffing.swift b/stdlib/public/core/Diffing.swift
@@ -388,6 +388,7 @@ fileprivate struct LinearMyers: ~Copyable {
       // Save the right side of the snake for later
       stack.append(tailBox)
     }
+    fatalError("Unreachable")
   }
   
   fileprivate mutating func middleSnake<T>(

Original file line number	Diff line number	Diff line change
`@@ -388,6 +388,7 @@ fileprivate struct LinearMyers: ~Copyable {`
`388`	`388`	`// Save the right side of the snake for later`
`389`	`389`	`stack.append(tailBox)`
`390`	`390`	`}`
	`391`	`+ fatalError("Unreachable")`
`391`	`392`	`}`
`392`	`393`
`393`	`394`	`fileprivate mutating func middleSnake<T>(`