## Fix Swift overloads producing uncompilable Java wrappers by Clemo97 · Pull Request #544 · swiftlang/swift-java

Clemo97 · 2026-01-29T15:38:43Z

Fixes #526

Problem

Swift allows method overloading using parameter labels (argument labels), where methods can have the same base name but different parameter labels:

public func takeValue(a: String) {}
public func takeValue(b: String) {}

In Swift, these are distinct methods because parameter labels are part of the function signature. However, when translated to Java, both were being generated with the same signature, causing compilation failures:

public void takeValue(String) //   Compilation error: duplicate method

Error:

error: method takeValue(String) is already defined in class OverloadSample

Solution

Modified the Java method name generation in FFMSwift2JavaGenerator+JavaTranslation.swift to append parameter labels as suffixes, creating unique method names that preserve Swift semantics while ensuring valid Java code.

Implementation:

Parameter labels are joined with underscores (e.g., _a, _b)
Applied consistently to all methods (functions, initializers)
Getters and setters are excluded to maintain property access patterns

Example transformation:

// Swift
public func takeValue(a: String) {}
public func takeValue(b: String) {}

// Generated Java (Before)
public void takeValue(String a) //   Duplicate!
public void takeValue(String b) //   Compilation error

// Generated Java (After)
public void takeValue_a(String a) //   Unique
public void takeValue_b(String b) //   Compiles successfully

Changes

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+JavaTranslation.swift: Added logic to append parameter labels to method names for disambiguation
Samples/SwiftJavaExtractFFMSampleApp/src/main/java/com/example/swift/HelloJava2Swift.java: Updated sample code to use new method naming convention (e.g., globalTakeInt_i(), init_len_cap())
Samples/SwiftJavaExtractFFMSampleApp/Sources/MySwiftLibrary/OverloadSample.swift: Added test cases with overloaded methods.

ktoso · 2026-01-29T16:40:58Z

Thanks for the request.what’s a reasonable direction however we should only be doing this if we detect a method has conflicts, otherwise it could be pretty annoying. Many members don’t have overloads and we can still call them with her normal names after all.

ktoso

Yeap still missing the required logic.

ktoso

marking as requesting changes

Clemo97 · 2026-02-03T08:18:04Z

Thanks for the request.what’s a reasonable direction however we should only be doing this if we detect a method has conflicts, otherwise it could be pretty annoying. Many members don’t have overloads and we can still call them with her normal names after all.

Yeah, my thought is to add a conflict detection logic one of the FFM directories that will collect all methods that will be generated from a class, compute each methods java signtature without suffixes then use that to detect duplicates from overloading and add parameter label suffixes to conflicting ones. @copilot

ktoso · 2026-02-03T09:29:15Z

I appreciate the will to help out but please don’t just at a coding assistant and expect it to figure out the implementation.

when you’re contributing you are ultimately responsible for the quality of the code. Feel free to use coding assistants but please verify and adjust their results such that they are passing our standards for quality and achieve the goals set out.

Back on the topic of implementation: yeah basically we’ll need such “conflicting names” mapping and then do another pass over them applying the renaming

Clemo97 · 2026-02-03T09:43:40Z

I appreciate the will to help out but please don’t just at a coding assistant and expect it to figure out the implementation.

when you’re contributing you are ultimately responsible for the quality of the code. Feel free to use coding assistants but please verify and adjust their results such that they are passing our standards for quality and achieve the goals set out.

Back on the topic of implementation: yeah basically we’ll need such “conflicting names” mapping and then do another pass over them applying the renaming

Thanks for the feedback.

ktoso · 2026-02-11T13:38:17Z

@Clemo97 are you working on this actively? I'm a bit confused with the periodic merges here but no action taken on the requested change?

ktoso · 2026-02-16T01:34:49Z

Samples/SwiftJavaExtractFFMSampleApp/src/main/java/com/example/swift/HelloJava2Swift.java

-            MySwiftLibrary.globalReceiveOptional_o1_o2(OptionalLong.of(12), Optional.of(dat));
+            var dat = Data.init(bytes, bytes.byteSize(), arena);
+            MySwiftLibrary.globalReceiveSomeDataProtocol(dat);
+            MySwiftLibrary.globalReceiveOptional(OptionalLong.of(12), Optional.of(dat));


cool, now we need actual tests for the conflicting behavior please :)

ktoso · 2026-02-16T01:35:44Z

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+JavaTranslation.swift

+  /// Detects method name conflicts within a nominal type and marks methods that need parameter label suffixes.
+  /// This implements a two-pass approach: first detect conflicts, then apply suffixes only where needed.
+  /// Only marks methods as conflicting if they would have identical Java signatures (same parameter types).
+  func detectMethodNameConflicts(for decl: ImportedNominalType) {


Can this be "detectJavaMethodNameDupes"? And can it please return a value instead of mutating self directly?

ktoso · 2026-02-16T01:36:49Z

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+JavaTranslation.swift

+      // Only mark methods as conflicting if they share the same Java signature
+      for group in signatureGroups where group.count > 1 {
+        for method in group {
+          methodsNeedingSuffixes.insert(ObjectIdentifier(method))


I don't love the ObjectIdentifier because it will be hard to debug and print those; can you please use some readable representation for the storage? Can be string names I guess

Maybe all this needs to become a class which is "DuplicateNames" and inside there do the storage, detection and everything -- that'll be much cleaner

ktoso · 2026-02-16T01:38:11Z

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+JavaTranslation.swift

  struct JavaTranslation {
    let config: Configuration
    var knownTypes: SwiftKnownTypes
+    let shouldAppendParameterLabels: Bool


Do we need this explicitly or should we pass the DuplicateNames call then during translate(), that might be cleaner than adding bools

ktoso · 2026-02-16T01:38:40Z

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+JavaTranslation.swift

+          // Conflict detected: append parameter labels for disambiguation
+          suffix = decl.functionSignature.parameters
+            .map { "_" + ($0.argumentLabel ?? "_") }
+            .joined()


Make this into a private method makeMethodNameWithParamsSuffix()

The whole "javaName = makeJavaMethodName(decl)" and put the logic there

Append parameter labels to Java method names for overload disambiguation

433ae80

Clemo97 requested a review from ktoso as a code owner January 29, 2026 15:38

Merge branch 'swiftlang:main' into main

b815641

ktoso reviewed Jan 30, 2026

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ktoso requested changes Jan 30, 2026

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Merge branch 'swiftlang:main' into main

77bac33

Clemo97 added 2 commits February 9, 2026 18:11

Merge branch 'swiftlang:main' into main

98e2c80

Merge branch 'swiftlang:main' into main

ddd27eb

Only add parameter label suffixes on Java signature conflicts

f5a9f78

ktoso reviewed Feb 16, 2026

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Clemo97 commented Jan 29, 2026 •

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ktoso commented Feb 3, 2026 •

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