From 28e27ffaf105f765b64a763962158b8216fbea6c Mon Sep 17 00:00:00 2001
From: "Bowen S. Zhu" <bowenzhu@mit.edu>
Date: Tue, 5 Nov 2024 11:00:56 -0500
Subject: [PATCH] Add `isequal2` function for checking metadata comparison

---
 src/types.jl   | 20 ++++++++++++++++++++
 test/basics.jl |  9 ++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/types.jl b/src/types.jl
index 2aca744b..64cd9667 100644
--- a/src/types.jl
+++ b/src/types.jl
@@ -267,6 +267,26 @@ function _isequal(a, b, E)
     end
 end
 
+"""
+$(TYPEDSIGNATURES)
+
+Checks for equality between two `BasicSymbolic` objects, considering both their
+values and metadata.
+
+The default `Base.isequal` function for `BasicSymbolic` only compares their expressions
+and ignores metadata. This can lead to hash collisions when metadata is relevant
+for distinguishing expressions, particularly in hashing contexts. This function
+provides a stricter equality check that includes metadata comparison, preventing
+such collisions.
+
+Modifying `Base.isequal` directly breaks numerous tests in `SymbolicUtils.jl` and
+downstream packages like `ModelingToolkit.jl`, hence the need for this separate
+function.
+"""
+function isequal2(a::BasicSymbolic, b::BasicSymbolic)::Bool
+    isequal(a, b) && isequal(metadata(a), metadata(b))
+end
+
 Base.one( s::Symbolic) = one( symtype(s))
 Base.zero(s::Symbolic) = zero(symtype(s))
 
diff --git a/test/basics.jl b/test/basics.jl
index 1402f9ac..93dfbd42 100644
--- a/test/basics.jl
+++ b/test/basics.jl
@@ -1,4 +1,4 @@
-using SymbolicUtils: Symbolic, Sym, FnType, Term, Add, Mul, Pow, symtype, operation, arguments, issym, isterm, BasicSymbolic, term
+using SymbolicUtils: Symbolic, Sym, FnType, Term, Add, Mul, Pow, symtype, operation, arguments, issym, isterm, BasicSymbolic, term, isequal2
 using SymbolicUtils
 using IfElse: ifelse
 using Setfield
@@ -336,6 +336,13 @@ end
 
     @test !isequal(a, missing)
     @test !isequal(missing, b)
+
+    a1 = setmetadata(a, Ctx1, "meta_1")
+    a2 = setmetadata(a, Ctx1, "meta_1")
+    a3 = setmetadata(a, Ctx2, "meta_2")
+    @test !isequal2(a, a1)
+    @test isequal2(a1, a2)
+    @test !isequal2(a1, a3)
 end
 
 @testset "subtyping" begin