BridgeJS: Support protocol refinement and constrained imports

A @js protocol may now refine other @js protocols declared in the same
module, and an imported generic function may be constrained to a @js
protocol:

    @js protocol NamedEntity: Identified, Named {}
    @js func describe(_ value: NamedEntity) -> String { ... }

    @js protocol Node: Identified, Named, BridgedSwiftGenericBridgeable {}
    @JSFunction func roundTrip<T: Node>(_ value: T) throws(JSException) -> T

Refinement is resolved by Swift, not by the generator. The JS-backed
implementations are emitted on the protocol itself, constrained to
wrapper types, and the Any<P> wrapper becomes a trivial struct:

    extension Identified where Self: _BridgedSwiftProtocolWrapper { var id: String { ... } }
    struct AnyIdentified: Identified, _BridgedSwiftProtocolWrapper { let jsObject: JSObject; ... }

AnyNamedEntity then satisfies Identified's and Named's requirements
through their extensions. Every extern stays owned by the protocol that
declares the member and is registered exactly once on the JS side, a
member the refining protocol re-declares resolves to the more specific
extension, and user conformers never see these defaults because they
do not conform to _BridgedSwiftProtocolWrapper. The d.ts mirrors this
with 'interface NamedEntity extends Identified, Named'. The skeleton
records only each protocol's own members plus the refinement edge
(inheritedJSProtocols). Refining a protocol from another module is
diagnosed on the inheritance clause.

Protocol wrapper extern thunks are now named by ABI name rather than
'_extern_<method>', so two protocols declaring the same member no
longer emit duplicate fileprivate declarations.

Generic imports accept @js protocols in the constraint, either composed
with BridgedSwiftGenericBridgeable or inheriting it through the
protocol; qualified names such as GraphKit.Node are preserved in the
generated Swift. A protocol that inherits BridgedSwiftGenericBridgeable
gets a synthesized Any<P>: BridgedSwiftGenericBridgeable conformance
and a registered type handle, so Any<P> can be used as a generic
argument. The generated TypeScript signature carries 'T extends Node'.

Skeletons written by earlier plugins still decode: a bare "T" generic
parameter is read as an unconstrained GenericParameter.

Runtime coverage drives a two-parent refinement with a re-declared
member, an inherited settable property, and a member-less refiner from
a single JS object, alongside the constrained-import round trips.

Author: krodak

Plugins/BridgeJS/Sources/BridgeJSCore/ExportSwift.swift

@@ -1425,7 +1425,7 @@ struct ProtocolCodegen {
         for method in proto.methods {
             let builder = try ImportTS.CallJSEmission(
                 moduleName: moduleName,
-                abiName: "_extern_\(method.name)",
+                abiName: method.abiName,
                 effects: method.effects,
                 returnType: method.returnType,
                 context: .exportSwift
@@ -1450,7 +1450,7 @@ struct ProtocolCodegen {
                 printer: externDeclPrinter,
                 moduleName: moduleName,
                 abiName: method.abiName,
-                functionName: "_extern_\(method.name)",
+                functionName: method.abiName,
                 abiParameters: builder.abiParameterSignatures,
                 returnType: builder.abiReturnType
             )
@@ -1478,32 +1478,42 @@ struct ProtocolCodegen {
             externDecls.append(contentsOf: propertyExternDecls)
         }
 
-        let structDeclPrinter = CodeFragmentPrinter()
-        structDeclPrinter.write("struct \(wrapperName): \(protocolName), _BridgedSwiftProtocolWrapper {")
-        structDeclPrinter.indent {
-            structDeclPrinter.write("let jsObject: JSObject")
-            structDeclPrinter.nextLine()
-
-            for methodDecl in methodDecls {
-                structDeclPrinter.write(lines: methodDecl.lines)
-                structDeclPrinter.nextLine()
-            }
-
-            for decl in propertyDecls {
-                structDeclPrinter.write(lines: decl.lines)
-                structDeclPrinter.nextLine()
+        // The JS-backed implementations live on the protocol itself, constrained
+        // to wrapper types. A refining protocol's wrapper (`AnyC` for
+        // `C: A, B`) then satisfies A's and B's requirements through their
+        // extensions: Swift's conformance resolution does the "flattening",
+        // every extern stays owned by the protocol that declares the member,
+        // and a member the refining protocol re-declares resolves to the more
+        // specific extension. User conformers never see these defaults - they
+        // do not conform to `_BridgedSwiftProtocolWrapper`.
+        var decls: [DeclSyntax] = []
+        if !methodDecls.isEmpty || !propertyDecls.isEmpty {
+            let extensionPrinter = CodeFragmentPrinter()
+            extensionPrinter.write("extension \(protocolName) where Self: _BridgedSwiftProtocolWrapper {")
+            extensionPrinter.indent {
+                var first = true
+                for decl in methodDecls + propertyDecls {
+                    if !first { extensionPrinter.nextLine() }
+                    first = false
+                    extensionPrinter.write(lines: decl.lines)
+                }
             }
-            structDeclPrinter.write(
-                multilineString: """
-                    static func bridgeJSLiftParameter(_ value: Int32) -> Self {
-                        return \(wrapperName)(jsObject: JSObject(id: UInt32(bitPattern: value)))
-                    }
-                    """
-            )
+            extensionPrinter.write("}")
+            decls.append("\(raw: extensionPrinter.lines.joined(separator: "\n"))")
         }
-        structDeclPrinter.write("}")
 
-        return ["\(raw: structDeclPrinter.lines.joined(separator: "\n"))"] + externDecls
+        decls.append(
+            """
+            struct \(raw: wrapperName): \(raw: protocolName), _BridgedSwiftProtocolWrapper {
+                let jsObject: JSObject
+
+                static func bridgeJSLiftParameter(_ value: Int32) -> Self {
+                    return \(raw: wrapperName)(jsObject: JSObject(id: UInt32(bitPattern: value)))
+                }
+            }
+            """
+        )
+        return decls + externDecls
     }
 
     private func renderProtocolProperty(

Plugins/BridgeJS/Sources/BridgeJSCore/ExternalModuleIndex.swift

@@ -7,6 +7,7 @@ public struct ExternalModuleIndex {
     public struct ExternalType: Equatable {
         public let moduleName: String
         public let bridgeType: BridgeType
+        public var isGenericBridgeableProtocol = false
     }
 
     public enum LookupResult: Equatable {
@@ -31,8 +32,12 @@ public struct ExternalModuleIndex {
             guard let exported = skeleton.exported else { continue }
             var moduleEntries = entriesByModule[moduleName] ?? [:]
 
-            func register(dotPath: String, bridgeType: BridgeType) {
-                let externalType = ExternalType(moduleName: moduleName, bridgeType: bridgeType)
+            func register(dotPath: String, bridgeType: BridgeType, isGenericBridgeableProtocol: Bool = false) {
+                let externalType = ExternalType(
+                    moduleName: moduleName,
+                    bridgeType: bridgeType,
+                    isGenericBridgeableProtocol: isGenericBridgeableProtocol
+                )
                 if moduleEntries[dotPath] == nil {
                     moduleEntries[dotPath] = externalType
                     entriesByDotPath[dotPath, default: []].append(externalType)
@@ -61,7 +66,11 @@ public struct ExternalModuleIndex {
                 register(dotPath: enumDef.swiftCallName, bridgeType: bridgeType)
             }
             for proto in exported.protocols {
-                register(dotPath: proto.name, bridgeType: .swiftProtocol(proto.name))
+                register(
+                    dotPath: proto.name,
+                    bridgeType: .swiftProtocol(proto.name),
+                    isGenericBridgeableProtocol: proto.isGenericBridgeable == true
+                )
             }
             for alias in exported.aliases {
                 register(

Plugins/BridgeJS/Sources/BridgeJSCore/ImportTS.swift

@@ -381,7 +381,7 @@ public struct ImportTS {
             parameters: [Parameter],
             returnType: BridgeType,
             effects: Effects,
-            genericParameters: [String] = []
+            genericParameters: [GenericParameter] = []
         ) -> DeclSyntax {
             let printer = CodeFragmentPrinter()
             let signature = SwiftSignatureBuilder.buildFunctionSignature(
@@ -393,7 +393,13 @@ public struct ImportTS {
             let genericClause =
                 genericParameters.isEmpty
                 ? ""
-                : "<" + genericParameters.map { "\($0): BridgedSwiftGenericBridgeable" }.joined(separator: ", ")
+                : "<"
+                    + genericParameters.map { genericParameter in
+                        let constraints =
+                            ["BridgedSwiftGenericBridgeable"]
+                            + (genericParameter.swiftConstraints ?? genericParameter.constraints)
+                        return "\(genericParameter.name): \(constraints.joined(separator: " & "))"
+                    }.joined(separator: ", ")
                     + ">"
             printer.write("func \(name.backtickIfNeeded())\(genericClause)\(signature) {")
             printer.indent {
@@ -465,7 +471,7 @@ public struct ImportTS {
                 parameters: function.parameters,
                 returnType: function.returnType,
                 effects: function.effects,
-                genericParameters: function.genericParameterNames
+                genericParameters: function.genericParameters ?? []
             )
             .with(\.leadingTrivia, Self.renderDocumentation(documentation: function.documentation))
         ]
@@ -496,7 +502,7 @@ public struct ImportTS {
                     parameters: [selfParameter] + method.parameters,
                     returnType: method.returnType,
                     effects: method.effects,
-                    genericParameters: method.genericParameterNames
+                    genericParameters: method.genericParameters ?? []
                 )
             ]
         }
@@ -522,7 +528,7 @@ public struct ImportTS {
                     parameters: method.parameters,
                     returnType: method.returnType,
                     effects: method.effects,
-                    genericParameters: method.genericParameterNames
+                    genericParameters: method.genericParameters ?? []
                 )
             ]
         }
@@ -548,7 +554,7 @@ public struct ImportTS {
                     parameters: constructor.parameters,
                     returnType: .jsObject(nil),
                     effects: effects,
-                    genericParameters: constructor.genericParameterNames
+                    genericParameters: constructor.genericParameters ?? []
                 )
             ]
         }