New unexpected compile behavior in Xcode 16.3

Programming Languages Swift
samkudr OP
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I have a macro that converts expression into a string literal, e.g.:

#toString(variable) -> "variable"
#toString(TypeName) -> "TypeName"
#toString(\TypeName.property) -> "property"

In Xcode 16.3 #toString(TypeName) stopped to work, compilation throws 'Expected member name or initializer call after type name' error. Everything works fine in Xcode 16.2. I tried to compare build settings between 16.2 and 16.3 but haven't noticed differences that may cause this new error.

The following works in both Xcode versions:

#toString(variable) -> "variable"
#toString(\TypeName.property) -> "property"

Seems like Xcode tries to compile code that shouldn't be compiled because of macro expansion.

Does anybody know what new has appeared in 16.3 and, perhaps, how to fix the problem?

Answered by samkudr in 833965022

Turned out that this is Xcode 16.3 which does it correctly.

According to the Expression Macros design, macro parameters should be type-checked, so the macro implementation doesn't receive incorrect code as input.

Thus Xcode <=16.2 erroneously allowed the wrong expression to be passed into my macro implementation, and this is fixed in Xcode 16.3.

Replies  5
Boosts 1
Views  381
Participants  3
YuantongL OP

Same found in my project, we have

@attached(member, names: arbitrary)
public macro MacroName<each U: ProtocolName>(_ name: repeat (each U).Type) =
  #externalMacro(module: "MacroModule", type: "MacroType")

and calling it

@MacroName(ImplementationOfProtocol)
struct Something { ...... }

class ImplementationOfProtocol: ProtocolName {}

Seeing error "Expected member name or initializer call after type name"
samkudr OP

Bug report: FB17081839.

DTS Engineer OP
Apple

I think you might get more traction on this issue oven on Swift Forums, and specifically the Development > Macros topic area there.

Share and Enjoy
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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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samkudr OP
Accepted Answer

Turned out that this is Xcode 16.3 which does it correctly.

According to the Expression Macros design, macro parameters should be type-checked, so the macro implementation doesn't receive incorrect code as input.

Thus Xcode <=16.2 erroneously allowed the wrong expression to be passed into my macro implementation, and this is fixed in Xcode 16.3.

DTS Engineer OP
Apple

Glad you got it sorted.

For those following along at home, samkudr’s thread on Swift Forums is here.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"