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Throw an error if types conforming to MemberMacro implement no expansion method #2319

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Merged
ahoppen merged 1 commit into from
Nov 1, 2023
Merged

Throw an error if types conforming to MemberMacro implement no expansion method #2319

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16 changes: 14 additions & 2 deletions Sources/SwiftSyntaxMacros/MacroProtocols/MemberMacro.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,9 @@ public protocol MemberMacro: AttachedMacro {
///
/// - Returns: the set of member declarations introduced by this macro, which
/// are nested inside the `attachedTo` declaration.
@available(*, deprecated, message: "Use expansion(of:providingMembersOf:conformingTo:in:")
///
/// - Warning: This is the legacy `expansion` function of `MemberMacro` that is provided for backwards-compatiblity.
/// Use ``expansion(of:providingMembersOf:conformingTo:in:)-1sxoe`` instead.
static func expansion(
of node: AttributeSyntax,
providingMembersOf declaration: some DeclGroupSyntax,
Expand Down Expand Up @@ -54,14 +56,24 @@ public protocol MemberMacro: AttachedMacro {
) throws -> [DeclSyntax]
}

private struct UnimplementedExpansionMethodError: Error, CustomStringConvertible {
var description: String {
"""
Types conforming to `MemberMacro` must implement either \
expansion(of:providingMembersOf:in:) or \
expansion(of:providingMembersOf:conformingTo:in:)
"""
}
}

public extension MemberMacro {
/// Default implementation supplies no conformances.
static func expansion(
of node: AttributeSyntax,
providingMembersOf declaration: some DeclGroupSyntax,
in context: some MacroExpansionContext
) throws -> [DeclSyntax] {
return try expansion(of: node, providingMembersOf: declaration, conformingTo: [], in: context)
throw UnimplementedExpansionMethodError()
}

/// Default implementation that ignores the unhandled conformances.
Expand Down