Unable to compile with Swift 6.2

[aputinski]

Description

I'm trying to upgrade my project that uses sqlite-data to Swift 6.2, but I was receiving errors from swift-structured-queries. I wanted to make sure I could just build the project, but I when I run swift build, here's what I get:

Apple Swift version 6.2 (swift-6.2-RELEASE)
2.	Compiling with the current language version
3.	While evaluating request TypeCheckPrimaryFileRequest(source_file "/_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift")
4.	While evaluating request TypeCheckFunctionBodyRequest(StructuredQueriesCore.(file).TableDraft extension._@/_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift:30:29)
5.	While type-checking statement at [/_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift:30:29 - line:32:3] RangeText="{
    SQLQueryExpression("\(PrimaryTable.self[keyPath: keyPath])")
  "
6.	While type-checking statement at [/_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift:31:5 - line:31:64] RangeText="SQLQueryExpression("\(PrimaryTable.self[keyPath: keyPath])""
7.	While type-checking-target starting at /_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift:31:5

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

The project builds

Actual behavior

Apple Swift version 6.2 (swift-6.2-RELEASE)
2.	Compiling with the current language version
3.	While evaluating request TypeCheckPrimaryFileRequest(source_file "/_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift")
4.	While evaluating request TypeCheckFunctionBodyRequest(StructuredQueriesCore.(file).TableDraft extension._@/_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift:30:29)
5.	While type-checking statement at [/_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift:30:29 - line:32:3] RangeText="{
    SQLQueryExpression("\(PrimaryTable.self[keyPath: keyPath])")
  "
6.	While type-checking statement at [/_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift:31:5 - line:31:64] RangeText="SQLQueryExpression("\(PrimaryTable.self[keyPath: keyPath])""
7.	While type-checking-target starting at /_playground/swift-structured-queries/Sources/StructuredQueriesCore/PrimaryKeyed.swift:31:5

Reproducing project

Check out main and run swift build using Swift 6.2

Structured Queries version information

0.23.1 (740c49c)

Destination operating system

macOS 15.7.1

Xcode version information

N/A

Swift Compiler version information

Apple Swift version 6.2 (swift-6.2-RELEASE)
Target: arm64-apple-macosx15.0
Build config: +assertions

[stephencelis]

Hi @aputinski, you appear to be using a build with +assertions, which triggers code paths in the compiler for potential compiler-related bugs. Official releases of Swift, including Xcode's toolchains and toolchains on Swift.org, disable these assertions. How are you going about installing Swift?

StructuredQueries employs a lot of advanced parameter pack functionality that Swift's compiler doesn't properly diagnose yet (and instead issues assertion failures). We'd love for this code to not crash the Swift compiler in these +assertions toolchains, and we've reported many, many bugs to the Swift project, but for now this project can only work in toolchains with assertions disabled.

There was a little discussion about making this behavior consistent recently on the forums: https://forums.swift.org/t/can-we-get-consistent-assertion-behavior-in-the-latest-release-swift-compiler-across-host-platforms/80545

While I empathize with folks maintaining with Windows and Android builds of Swift, enabling assertions makes advanced uses of parameter packs impossible, and thus projects like StructuredQueries.

Because this is not a bug with the project, and instead related to bugs in Swift, I'm going to convert to a discussion.

[stephencelis]

Just a follow-up, but SPI shows 6.2 compatibility for most platforms here: https://swiftpackageindex.com/pointfreeco/swift-structured-queries

Only Wasm and Android are not compiling, and we will gladly take any fixes for issues preventing those platforms from building.

[aputinski]

Thanks for the quick reply. I've installed Swift using swiftly (because I was trying to cross compile a Linux build of my app). Looks like I might need to abandon that idea all together?

[aputinski]

I apologize — I'm new to running Swift outside of Xcode.
Running swift build -c release gives me the exact same error.
Do I need to so something else?

[stephencelis]

@aputinski I believe you must use an Xcode installation, or an official point release toolchain downloaded off swift.org. Notably you should not see +assertions when inquiring swiftc -v.

I think maybe you can cross-compile to Linux using the latest Xcode 26+? You might also want to start a discussion on the Swift forums. There are folks there with more experience with this kind of thing.

[aputinski]

Thanks!

[coenttb]

I also ran into this issue.

In particular Swift 6.2.0 (stable release) crashes during command line swift build and swift test.

I observe that Swift 6.2.1 (Xcode 26.1 beta) fixes the build crash, but swift test fails with swift-syntax 602.0.0 (stable release).
Two different errors that I came accross:

Error 1 - Linker error:

error: link command failed with exit code 1 (use -v to see invocation)
Undefined symbols for architecture arm64:
  "SwiftSyntax.SyntaxRewriter.(visitationFunc in _F0C5D882E9301122F145EADC4573BFC8)(for: SwiftSyntax.Syntax) -> (SwiftSyntax.Syntax) -> SwiftSyntax.Syntax", referenced from:
      full type metadata for StructuredQueriesMacros.SelfRewriter in SelfRewriter.swift.o
ld: symbol(s) not found for architecture arm64

Error 2 - Missing module:

Tests/StructuredQueriesMacrosTests/BindMacroTests.swift:2:8: error: missing required module 'SwiftCompilerPlugin'
 1 | import MacroTesting
 2 | import StructuredQueriesMacros
   |        `- error: missing required module 'SwiftCompilerPlugin'

Workaround: swift test works using beta Xcode+toolchain (6.2.1) and swift-syntax development snapshot (e.g.: branch: "swift-6.2-DEVELOPMENT-SNAPSHOT-2025-10-09-a").
xcbuild also works in all tested configurations.

Swift Version	swift-syntax Version	swift build	swift test	Status
6.2.0 (stable)	602.0.0 (stable)	❌ Crash	N/A	Unusable1
6.2.1 (beta)	602.0.0 (stable)	✅ Pass	❌ Fail	Can't test2
6.2.1 (beta)	swift-6.2-DEVELOPMENT-SNAPSHOT (dev)	✅ Pass	✅ Pass	Works (all beta)

Footnotes

1. Swift 6.2.0 crashes during compilation at CSSimplify.cpp:16157 in addKeyPathApplicationRootConstraint when processing opaque optional types like (some QueryExpression<Bool>)?. Occurs while compiling Sources/StructuredQueriesCore/Statements/Where.swift:76. ↩

2. Two different failures with swift-syntax 602.0.0: (1) Linker error: Missing SwiftSyntax internal symbols. SelfRewriter references SwiftSyntax.SyntaxRewriter.visitationFunc which isn't exposed. (2). Module error: Test targets can't import macro targets because SwiftCompilerPlugin is bundled in the macro but not exposed in its module interface. ↩

[mbrandonw]

@coenttb Are you using swiftly as mentioned above in this discussion?

[coenttb]

I was using swiftly in the failing cases.

[mbrandonw]

Ok, as mentioned above, swiftly is built with assertions turned on and what seems to be perfectly valid Swift code can cause the Swift compiler to crash. It's hard to prioritize fixing these errors because they are hard to track down, they don't affect the Xcode toolchains or even Linux toolchains, and it's not clear why assertions are turned on for swiftly but not other toolchains. If anyone who uses swiftly regularly wants to help us tackle these crashes we would happily take the help.

[jshier]

Assertions are turned on for all macOS Swift builds except Xcode's, and swiftly only installs those types of builds. Frankly, unless you're testing specific things about specific toolchains, swiftly isn't very useful on macOS, as it interferes with the ability to use Xcode's toolchains, and you can't use any of its toolchains to ship software to Apple's stores. The 6.2 release build it installs is NOT the same as the 6.2 release builds in Xcode.