[SR-15736] compiler crashes if a generic result-builder contains a for-loop

[kelvin13]

Previous ID	SR-15736
Radar	None
Original Reporter	@kelvin13
Type	Bug

Environment

$ swiftenv version
DEVELOPMENT-SNAPSHOT-2022-01-09-a
$ swift --version
Swift version 5.6-dev (LLVM 7b20e61dd04138a, Swift 9438cf6)
Target: x86_64-unknown-linux-gnu

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: a43ed93d3615c72ad24c46a859ca0f4e

Issue Description:

as of DEVELOPMENT-SNAPSHOT-2022-01-09-a, using any result-builder in a generic context will crash the compiler, if the result-builder contains a for-loop.

Minimal reproduction:

func foo<T>(repeating value:T) -> [T]
{
    return Builder<T>.array
    {
        for _:Int in [1, 2, 3] as [Int]
        {
            value
        }
    }
}

@resultBuilder 
enum Builder<Element> 
{
    static 
    func array(@Builder<Element> _ elements:() -> [Element]) -> [Element]
    {
        elements()
    }
    
    static 
    func buildExpression(_ element:Element) -> [Element]
    {
        [element]
    }
    static 
    func buildExpression(_ elements:[Element]) -> [Element]
    {
        elements
    }
    static 
    func buildBlock(_ elements:[Element]...) -> [Element]
    {
        elements.flatMap{ $0 }
    }
    static 
    func buildArray(_ elements:[[Element]]) -> [Element]
    {
        elements.flatMap{ $0 }
    }
}

crashes with:

$ swiftc result-builder-crash.swift 
error: compile command failed due to signal 6 (use -v to see invocation)
swift-frontend: /home/build-user/swift/lib/AST/TypeCheckRequests.cpp:981: void swift::InterfaceTypeRequest::cacheResult(swift::Type) const: Assertion `!type->hasArchetype() && "Archetype in interface type"' failed.
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the project and the crash backtrace.
Stack dump:
0.  Program arguments: .swiftenv/versions/DEVELOPMENT-SNAPSHOT-2022-01-09-a/usr/bin/swift-frontend -frontend -c -primary-file result-builder-crash.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -color-diagnostics -new-driver-path /home/klossy/.swiftenv/versions/DEVELOPMENT-SNAPSHOT-2022-01-09-a/usr/bin/swift-driver -resource-dir .swiftenv/versions/DEVELOPMENT-SNAPSHOT-2022-01-09-a/usr/lib/swift -module-name main -o /tmp/TemporaryDirectory.YHE35r/result-builder-crash-1.o
1.  Swift version 5.6-dev (LLVM 7b20e61dd04138a, Swift 9438cf6b2e83c5f)
2.  Compiling with the current language version
3.  While evaluating request TypeCheckSourceFileRequest(source_file "result-builder-crash.swift")
4.  While evaluating request TypeCheckFunctionBodyRequest(main.(file).foo(repeating:)@result-builder-crash.swift:1:6)
5.  While type-checking statement at [result-builder-crash.swift:2:1 - line:10:1] RangeText="{
    return Builder<T>.array
    {
        for _:Int in [1, 2, 3] as [Int]
        {
            value
        }
    }
"
6.  While type-checking statement at [result-builder-crash.swift:3:5 - line:9:5] RangeText="return Builder<T>.array
    {
        for _:Int in [1, 2, 3] as [Int]
        {
            value
        }
    "
7.  While type-checking expression at [result-builder-crash.swift:3:12 - line:9:5] RangeText="Builder<T>.array
    {
        for _:Int in [1, 2, 3] as [Int]
        {
            value
        }
    "

Replacing the parameter `T` with a concrete type such as `Int` will compile normally.