4 files changed, 53 insertions, 18 deletions
diff --git a/cpp/src/Slice/JavaUtil.cpp b/cpp/src/Slice/JavaUtil.cpp
index ad20211a1c7..9ad435fbae7 100644
--- a/cpp/src/Slice/JavaUtil.cpp
+++ b/cpp/src/Slice/JavaUtil.cpp
@@ -669,6 +669,28 @@ Slice::computeSerialVersionUUID(const ExceptionPtr& p)
     return hashCode;
 }
 
+bool
+Slice::isValidMethodParameterList(const DataMemberList& members, int additionalUnits)
+{
+    // The maximum length of a method parameter list is 255 units, including the implicit 'this' parameter.
+    // Each parameter is 1 unit, except for long and double parameters, which are 2 units.
+    // Start the length at 1 to account for the implicit 'this' parameter (plus any additional units).
+    int length = 1 + additionalUnits;
+    for(DataMemberList::const_iterator p = members.begin(); p != members.end(); ++p)
+    {
+        BuiltinPtr builtin = BuiltinPtr::dynamicCast((*p)->type());
+        if(builtin && (builtin->kind() == Builtin::KindLong || builtin->kind() == Builtin::KindDouble))
+        {
+            length += 2;
+        }
+        else
+        {
+            length++;
+        }
+    }
+    return length <= 255;
+}
+
 Slice::JavaOutput::JavaOutput()
 {
 }
diff --git a/cpp/src/Slice/JavaUtil.h b/cpp/src/Slice/JavaUtil.h
index 326d7adfa1a..d9c6e440d0c 100644
--- a/cpp/src/Slice/JavaUtil.h
+++ b/cpp/src/Slice/JavaUtil.h
@@ -29,6 +29,15 @@ computeSerialVersionUUID(const ExceptionPtr&);
 long
 computeSerialVersionUUID(const StructPtr&);
 
+//
+// Returns true if we can generate a method from the given data member list. A Java method
+// can have a maximum of 255 parameters (including the implicit 'this') where each parameter
+// is counted as 1 unit, except for long and double which are counted as 2 units.
+// See https://docs.oracle.com/javase/specs/jvms/se20/html/jvms-4.html#jvms-4.3.3
+//
+bool
+isValidMethodParameterList(const DataMemberList&, int additionalUnits = 0);
+
 class JavaOutput : public ::IceUtilInternal::Output
 {
 public:
diff --git a/cpp/src/slice2java/Gen.cpp b/cpp/src/slice2java/Gen.cpp
index dbd2ddfd280..7cd4c75f268 100644
--- a/cpp/src/slice2java/Gen.cpp
+++ b/cpp/src/slice2java/Gen.cpp
@@ -2552,9 +2552,9 @@ Slice::Gen::TypesVisitor::visitClassDefStart(const ClassDefPtr& p)
         out << eb;
 
         //
-        // A method cannot have more than 255 parameters (including the implicit "this" argument).
+        // Generate constructor if the parameter list is not too large.
         //
-        if(allDataMembers.size() < 255)
+        if(isValidMethodParameterList(allDataMembers))
         {
             DataMemberList baseDataMembers;
             if(baseClass)
@@ -2945,9 +2945,9 @@ Slice::Gen::TypesVisitor::visitExceptionStart(const ExceptionPtr& p)
         }
 
         //
-        // A method cannot have more than 255 parameters (including the implicit "this" argument).
+        // Generate constructor if the parameter list is not too large.
         //
-        if(allDataMembers.size() < 255)
+        if(isValidMethodParameterList(allDataMembers))
         {
             if(hasRequiredMembers && hasOptionalMembers)
             {
@@ -3010,8 +3010,9 @@ Slice::Gen::TypesVisitor::visitExceptionStart(const ExceptionPtr& p)
 
                 //
                 // Create constructor that takes all data members plus a Throwable.
+                // Do this only when the parameter list is not too large.
                 //
-                if(allDataMembers.size() < 254)
+                if(isValidMethodParameterList(allDataMembers, 1))
                 {
                     const string causeParamName = getEscapedParamName(allDataMembers, "cause");
 
@@ -3090,9 +3091,10 @@ Slice::Gen::TypesVisitor::visitExceptionStart(const ExceptionPtr& p)
             out << eb;
 
             //
-            // Create constructor that takes all data members plus a Throwable
+            // Create constructor that takes all data members plus a Throwable.
+            // Do this only when the parameter list is not too large.
             //
-            if(allDataMembers.size() < 254)
+            if(isValidMethodParameterList(allDataMembers, 1))
             {
                 const string causeParamName = getEscapedParamName(allDataMembers, "cause");
 
@@ -3382,9 +3384,9 @@ Slice::Gen::TypesVisitor::visitStructEnd(const StructPtr& p)
     out << eb;
 
     //
-    // A method cannot have more than 255 parameters (including the implicit "this" argument).
+    // Generate constructor if the parameter list is not too large.
     //
-    if(members.size() < 255)
+    if(isValidMethodParameterList(members))
     {
         vector<string> paramDecl;
         vector<string> paramNames;
diff --git a/cpp/src/slice2java/GenCompat.cpp b/cpp/src/slice2java/GenCompat.cpp
index b3f5504f741..eb76ecbe9cf 100644
--- a/cpp/src/slice2java/GenCompat.cpp
+++ b/cpp/src/slice2java/GenCompat.cpp
@@ -2945,9 +2945,9 @@ Slice::GenCompat::TypesVisitor::visitClassDefStart(const ClassDefPtr& p)
         out << eb;
 
         //
-        // A method cannot have more than 255 parameters (including the implicit "this" argument).
+        // Generate constructor if the parameter list is not too large.
         //
-        if(allDataMembers.size() < 255)
+        if(isValidMethodParameterList(members))
         {
             DataMemberList baseDataMembers;
             if(baseClass)
@@ -3255,9 +3255,9 @@ Slice::GenCompat::TypesVisitor::visitExceptionStart(const ExceptionPtr& p)
         }
 
         //
-        // A method cannot have more than 255 parameters (including the implicit "this" argument).
+        // Generate constructor if the parameter list is not too large.
         //
-        if(allDataMembers.size() < 255)
+        if(isValidMethodParameterList(members))
         {
             if(hasRequiredMembers && hasOptionalMembers)
             {
@@ -3319,8 +3319,9 @@ Slice::GenCompat::TypesVisitor::visitExceptionStart(const ExceptionPtr& p)
 
                 //
                 // Create constructor that takes all data members plus a Throwable.
+                // Do this only when the parameter list is not too large.
                 //
-                if(allDataMembers.size() < 254)
+                if(isValidMethodParameterList(allDataMembers, 1))
                 {
                     const string causeParamName = getEscapedParamName(allDataMembers, "cause");
                     paramDecl.push_back("Throwable " + causeParamName);
@@ -3397,9 +3398,10 @@ Slice::GenCompat::TypesVisitor::visitExceptionStart(const ExceptionPtr& p)
             out << eb;
 
             //
-            // Create constructor that takes all data members plus a Throwable
+            // Create constructor that takes all data members plus a Throwable.
+            // Do this only when the parameter list is not too large.
             //
-            if(allDataMembers.size() < 254)
+            if(isValidMethodParameterList(allDataMembers, 1))
             {
                 const string causeParamName = getEscapedParamName(allDataMembers, "cause");
                 paramDecl.push_back("Throwable " + causeParamName);
@@ -3670,9 +3672,9 @@ Slice::GenCompat::TypesVisitor::visitStructEnd(const StructPtr& p)
     out << eb;
 
     //
-    // A method cannot have more than 255 parameters (including the implicit "this" argument).
+    // Generate constructor if the parameter list is not too large.
     //
-    if(members.size() < 255)
+    if(isValidMethodParameterList(members))
     {
         vector<string> paramDecl;
         vector<string> paramNames;