Swift 6.3-dev compiler crashes - workarounds applied

[doozMen]

Summary

Swift 6.3-dev (swift-DEVELOPMENT-SNAPSHOT-2025-12-11-a) crashes when compiling certain code patterns. This issue tracks the workarounds applied to enable building with Swift 6.3.

Compiler Bug

Assertion failed: (Start.isValid() == End.isValid() && "Start and end should either both be valid or both be invalid!"), function SourceRange, file SourceLoc.h, line 161.

Workarounds Applied

1. PrimaryKeyMigration.swift

• SyncEngine.migratePrimaryKeys() - guarded with #if !compiler(>=6.3)
• PrimaryKeyedTable.migratePrimaryKeyToUUID() - guarded with #if !compiler(>=6.3)
• Reason: #sql macro + $backfillUUID macro-generated function crashes compiler

2. Statement+GRDB.swift

• SelectStatement.find(_:key:) - guarded with #if !compiler(>=6.3)
• Reason: Depends on Select.find() which is guarded in swift-structured-queries

Impact

• Swift < 6.3: Full functionality available
• Swift >= 6.3: CloudKit primary key migration and find(key:) methods unavailable

Related Changes in swift-structured-queries

• PrimaryKeyed.swift - closures with opaque type sequences
• Select.swift - variadic generics pack expansion

TODO

• Report minimal reproducer to https://github.com/apple/swift/issues
• Re-enable when Swift 6.3 stabilizes
• Test with newer Swift snapshots periodically