BridgeJS: Support generic functions at the Swift and JavaScript boundary

Author: krodak

Plugins/BridgeJS/README.md

@@ -98,7 +98,7 @@ graph LR
 | `Dictionary<K, V>` | `Record<K, V>` | - | [#495](https://github.com/swiftwasm/JavaScriptKit/issues/495) |
 | `Set<T>` | `Set<T>` | - | [#397](https://github.com/swiftwasm/JavaScriptKit/issues/397) |
 | `Foundation.URL` | `string` | - | [#496](https://github.com/swiftwasm/JavaScriptKit/issues/496) |
-| Generics | - | - | [#398](https://github.com/swiftwasm/JavaScriptKit/issues/398) |
+| Generic top-level function (`T`, `[T]`, `T?`, `[String: T]`) | `<T>(value: T, type: BridgeType<T>)` | Depends on `T` | ✅ |
 
 ### Import-specific (TypeScript -> Swift)
 

Plugins/BridgeJS/Sources/BridgeJSCore/ExportSwift.swift

@@ -143,6 +143,11 @@ public struct ImportTS {
         }
 
         func lowerParameter(param: Parameter) throws {
+            if let genericPush = param.type.genericStackPushStatement(value: param.name) {
+                stackLoweringStmts.insert(genericPush, at: 0)
+                return
+            }
+
             let loweringInfo = try param.type.loweringParameterInfo(context: context)
 
             switch param.type {
@@ -241,6 +246,12 @@ public struct ImportTS {
             abiParameterForwardings.insert(contentsOf: ["resolveRef", "rejectRef"], at: 0)
         }
 
+        func appendTypeIDParameter(index: Int, genericParameterName: String) {
+            let abiParamName = "_generic\(index)TypeId"
+            abiParameterSignatures.append((abiParamName, .i32))
+            abiParameterForwardings.append("\(genericParameterName).bridgeJSTypeID")
+        }
+
         func call() throws {
             for stmt in stackLoweringStmts {
                 body.write(stmt.description)
@@ -297,14 +308,18 @@ public struct ImportTS {
                 body.write("return \(returnType.swiftType).bridgeJSLiftReturnFromSideChannel()")
             } else {
                 let liftExpr: String
-                switch returnType {
-                case .closure(let signature, _):
-                    liftExpr = "_BJS_Closure_\(signature.mangleName).bridgeJSLift(ret)"
-                default:
-                    if liftingInfo.valueToLift != nil {
-                        liftExpr = "\(returnType.swiftType).bridgeJSLiftReturn(ret)"
-                    } else {
-                        liftExpr = "\(returnType.swiftType).bridgeJSLiftReturn()"
+                if let genericPop = returnType.genericStackPopExpression {
+                    liftExpr = genericPop
+                } else {
+                    switch returnType {
+                    case .closure(let signature, _):
+                        liftExpr = "_BJS_Closure_\(signature.mangleName).bridgeJSLift(ret)"
+                    default:
+                        if liftingInfo.valueToLift != nil {
+                            liftExpr = "\(returnType.swiftType).bridgeJSLiftReturn(ret)"
+                        } else {
+                            liftExpr = "\(returnType.swiftType).bridgeJSLiftReturn()"
+                        }
                     }
                 }
                 body.write("return \(liftExpr)")
@@ -363,7 +378,8 @@ public struct ImportTS {
             name: String,
             parameters: [Parameter],
             returnType: BridgeType,
-            effects: Effects
+            effects: Effects,
+            genericParameters: [String] = []
         ) -> DeclSyntax {
             let printer = CodeFragmentPrinter()
             let signature = SwiftSignatureBuilder.buildFunctionSignature(
@@ -372,7 +388,12 @@ public struct ImportTS {
                 effects: effects,
                 useWildcardLabels: true
             )
-            printer.write("func \(name.backtickIfNeeded())\(signature) {")
+            let genericClause =
+                genericParameters.isEmpty
+                ? ""
+                : "<" + genericParameters.map { "\($0): _BridgedSwiftGenericBridgeable" }.joined(separator: ", ")
+                    + ">"
+            printer.write("func \(name.backtickIfNeeded())\(genericClause)\(signature) {")
             printer.indent {
                 printer.write(lines: body.lines)
             }
@@ -432,6 +453,9 @@ public struct ImportTS {
         for param in function.parameters {
             try builder.lowerParameter(param: param)
         }
+        for (index, genericParam) in (function.genericParameters ?? []).enumerated() {
+            builder.appendTypeIDParameter(index: index, genericParameterName: genericParam)
+        }
         try builder.call()
         try builder.liftReturnValue()
         topLevelDecls.append(builder.renderImportDecl())
@@ -440,7 +464,8 @@ public struct ImportTS {
                 name: Self.thunkName(function: function),
                 parameters: function.parameters,
                 returnType: function.returnType,
-                effects: function.effects
+                effects: function.effects,
+                genericParameters: function.genericParameters ?? []
             )
             .with(\.leadingTrivia, Self.renderDocumentation(documentation: function.documentation))
         ]
@@ -959,6 +984,8 @@ extension BridgeType {
             return LoweringParameterInfo(loweredParameters: [])
         case .alias:
             preconditionFailure("`.alias` must be resolved by `.unaliased` before reaching loweringParameterInfo")
+        case .generic:
+            return LoweringParameterInfo(loweredParameters: [])
         }
     }
 
@@ -1033,6 +1060,8 @@ extension BridgeType {
             return LiftingReturnInfo(valueToLift: nil)
         case .alias:
             preconditionFailure("`.alias` must be resolved by `.unaliased` before reaching liftingReturnInfo")
+        case .generic:
+            return LiftingReturnInfo(valueToLift: nil)
         }
     }
 }