From 1c6e2413957007475e5145a1d837b05d88df06c2 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Tue, 10 Sep 2024 08:13:52 -0700
Subject: Disambiguate subscript decls by preferring the one with more
 accessors. (#5046)

---
 source/slang/slang-check-overload.cpp | 41 +++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

(limited to 'source')

diff --git a/source/slang/slang-check-overload.cpp b/source/slang/slang-check-overload.cpp
index 9b3d6baff..3b36b270b 100644
--- a/source/slang/slang-check-overload.cpp
+++ b/source/slang/slang-check-overload.cpp
@@ -1199,6 +1199,8 @@ namespace Slang
         return parent;
     }
 
+    // Returns -1 if left is preferred, 1 if right is preferred, and 0 if they are equal.
+    //
     int SemanticsVisitor::CompareLookupResultItems(
         LookupResultItem const& left,
         LookupResultItem const& right)
@@ -1283,6 +1285,45 @@ namespace Slang
                     return -1;
         }
 
+        // If both are subscript decls, prefer the one that provides more
+        // accessors.
+        if (auto leftSubscriptDecl = left.declRef.as<SubscriptDecl>())
+        {
+            if (auto rightSubscriptDecl = right.declRef.as<SubscriptDecl>())
+            {
+                auto leftAccessorCount = leftSubscriptDecl.getDecl()->getMembersOfType<AccessorDecl>().getCount();
+                auto rightAccessorCount = rightSubscriptDecl.getDecl()->getMembersOfType<AccessorDecl>().getCount();
+                auto decl1IsSubsetOfDecl2 = [=](SubscriptDecl* decl1, SubscriptDecl* decl2)
+                    {
+                        for (auto accessorDecl1 : decl1->getMembersOfType<AccessorDecl>())
+                        {
+                            bool found = false;
+                            for (auto accessorDecl2 : decl2->getMembersOfType<AccessorDecl>())
+                            {
+                                if (accessorDecl1->astNodeType == accessorDecl2->astNodeType)
+                                {
+                                    found = true;
+                                    break;
+                                }
+                            }
+                            if (!found)
+                                return false;
+                        }
+                        return true;
+                    };
+                if (leftAccessorCount > rightAccessorCount
+                    && decl1IsSubsetOfDecl2(rightSubscriptDecl.getDecl(), leftSubscriptDecl.getDecl()))
+                {
+                    return -1;
+                }
+                else if (rightAccessorCount > leftAccessorCount
+                    && decl1IsSubsetOfDecl2(leftSubscriptDecl.getDecl(), rightSubscriptDecl.getDecl()))
+                {
+                    return 1;
+                }
+            }
+        }
+
         // TODO: We should generalize above rules such that in a tie a declaration
         // A::m is better than B::m when all other factors are equal and
         // A inherits from B.
-- 
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