Update macro template to support Swift Testing tests #8890

[MaelRB]

Add support for macro project using Swift Testing in InitPackage.

Motivation:

Since the introduction of SwiftSyntaxMacrosGenericTestSupport, Swift Testing should be supported to test macro

Modifications:

• Update writeMacroTestsFile to support Swift Testing
• Use MacroSpec for both XCTest and Swift Testing
• Remove swift-testing dependency from the Package manifest when building macro template for Swift Testing
• Remove unsupportedTestingLibraryForPackageType error as it's unused
• Add unit tests for macro template generation

Result:

Generated test file when using Swift Testing:

import SwiftSyntax
import SwiftSyntaxBuilder
import SwiftSyntaxMacros
import SwiftSyntaxMacroExpansion
import Testing
import SwiftSyntaxMacrosGenericTestSupport

// Macro implementations build for the host, so the corresponding module is not available when cross-compiling. Cross-compiled tests may still make use of the macro itself in end-to-end tests.
#if canImport(fooMacros)
import fooMacros

let testMacros: [String: MacroSpec] = [
    "stringify": MacroSpec(type: StringifyMacro.self),
]
#endif

struct fooTests {
    
    @Test
    func macro() {
#if canImport(fooMacros)
        assertMacroExpansion(
            """
            #stringify(a + b)
            """,
            expandedSource: """
            (a + b, "a + b")
            """,
            macroSpecs: testMacros
        ) {
            Issue.record(
                "\($0.message)",
                sourceLocation:
                    SourceLocation(
                        fileID: $0.location.fileID,
                        filePath: $0.location.filePath,
                        line: $0.location.line,
                        column: $0.location.column
                    )
            )
        }
#else
        Issue.record("macros are only supported when running tests for the host platform")
#endif
    }
    
    @Test
    func macroWithStringLiteral() {
#if canImport(fooMacros)
        assertMacroExpansion(
            #"""
            #stringify("Hello, \(name)")
            """#,
            expandedSource: #"""
            ("Hello, \(name)", #""Hello, \(name)""#)
            """#,
            macroSpecs: testMacros
        ) {
            Issue.record(
                "\($0.message)",
                sourceLocation:
                    SourceLocation(
                        fileID: $0.location.fileID,
                        filePath: $0.location.filePath,
                        line: $0.location.line,
                        column: $0.location.column
                    )
            )
        }
#else
        Issue.record("macros are only supported when running tests for the host platform")
#endif
    }
}

Fixes: #8890

[bkhouri]

This resolves #8890

[vanvoorden]

Ahh… just found this one! I hope we can ship a solution to this soon.

FWIW it might be worth highlighting something to engineers reminding them this support would require swift-syntax 600:

#if canImport(SwiftSyntax600)
...
#else
// error? or warning?
#endif

It might be confusing to engineers if they create a macro target with this template and then try to back support swift-syntax 510.

[vanvoorden]

Maybe we should also import SwiftSyntaxMacrosGenericTestSupport?

Ahh… nevermind… I see it below!

[vanvoorden]

Style nit: Could this be refactored to an extension on Issue? Then we can put this work in one place instead of duplicated it across N different tests?

[vanvoorden]

extension Issue {
  @discardableResult static func record(_ failure: TestFailureSpec) -> Self {
    Self.record(
      Comment(rawValue: failure.message),
      sourceLocation: SourceLocation(
        fileID: failure.location.fileID,
        filePath: failure.location.filePath,
        line: failure.location.line,
        column: failure.location.column
      )
    )
  }
}

cc @grynspan Was there anything blocking us from shipping that extension directly in swift-testing? Or is there another canonical way to bridge between SwiftSyntaxMacrosGenericTestSupport.TestFailureSpec and Testing.Issue?

[vanvoorden]

We could also choose to factor this to a free function:

func failureHander(_ failure: TestFailureSpec) {
  Issue.record(
    Comment(rawValue: failure.message),
    sourceLocation:
      SourceLocation(
        fileID: failure.location.fileID,
        filePath: failure.location.filePath,
        line: failure.location.line,
        column: failure.location.column
      )
  )
}

And then pass that failureHander to every test similar to how we pass testMacros.

[grynspan]

Swift Testing cannot directly link to swift-syntax since it doesn't exist in the toolchain at runtime. That means we cannot export any symbols that reference types from swift-syntax (except in our macro target which is only loaded/run at compile time.)

[bkhouri]

we should work the the swift-syntax owners and the Testing Workgroup to ensure this aligns with the overall vision.