From e0196cfdaf6f5a1a6cf8136345d013a5903df399 Mon Sep 17 00:00:00 2001
From: Aayush Sabharwal <aayush.sabharwal@gmail.com>
Date: Thu, 30 Jan 2025 20:44:44 +0530
Subject: [PATCH 1/2] fix: fix `fast_substitute` on subarrays of symbolic
 variables

---
 src/variable.jl | 2 ++
 test/utils.jl   | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/src/variable.jl b/src/variable.jl
index 37ba40271..9d9cc260a 100644
--- a/src/variable.jl
+++ b/src/variable.jl
@@ -606,6 +606,7 @@ function fast_substitute(expr, subs; operator = Nothing)
         canfold = Ref(!(op isa Symbolic))
         args = let canfold = canfold
             map(args) do x
+                symbolic_type(x) == NotSymbolic() && !is_array_of_symbolics(x) && return x
                 x′ = fast_substitute(x, subs; operator)
                 canfold[] = canfold[] && (symbolic_type(x′) == NotSymbolic() && !is_array_of_symbolics(x′))
                 x′
@@ -633,6 +634,7 @@ function fast_substitute(expr, pair::Pair; operator = Nothing)
         canfold = Ref(!(op isa Symbolic))
         args = let canfold = canfold
             map(args) do x
+                symbolic_type(x) == NotSymbolic() && !is_array_of_symbolics(x) && return x
                 x′ = fast_substitute(x, pair; operator)
                 canfold[] = canfold[] && (symbolic_type(x′) == NotSymbolic() && !is_array_of_symbolics(x′))
                 x′
diff --git a/test/utils.jl b/test/utils.jl
index 8203b41f6..a4f3db467 100644
--- a/test/utils.jl
+++ b/test/utils.jl
@@ -162,3 +162,11 @@ end
     ex2 = Symbolics.fixpoint_sub(ex, Dict(y => 1.0, z => 2.0))
     @test isequal(ex2, foo([x, 1.0], 2.0))
 end
+
+@testset "`fast_substitute` of subarray symbolics" begin
+    @variables p[1:4] q[1:5]
+    @test isequal(p[1:2], Symbolics.fast_substitute(p[1:2], Dict()))
+    @test isequal(p[1:2], Symbolics.fast_substitute(p[1:2], p => p))
+    @test isequal(q[1:2], Symbolics.fast_substitute(p[1:2], Dict(p => q)))
+    @test isequal(q[1:2], Symbolics.fast_substitute(p[1:2], p => q))
+end

From 16df6db70e586f5d2bee87dfc487a532c2216d15 Mon Sep 17 00:00:00 2001
From: Aayush Sabharwal <aayush.sabharwal@gmail.com>
Date: Fri, 31 Jan 2025 12:58:41 +0530
Subject: [PATCH 2/2] fix: fix `build_function` for array symbolics

---
 src/build_function.jl  | 15 ++++++++-------
 test/build_function.jl | 11 +++++++++++
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/src/build_function.jl b/src/build_function.jl
index 34d53481e..0a6c152dc 100644
--- a/src/build_function.jl
+++ b/src/build_function.jl
@@ -132,7 +132,7 @@ end
 
 SymbolicUtils.Code.get_rewrites(x::Arr) = SymbolicUtils.Code.get_rewrites(unwrap(x))
 
-function _build_function(target::JuliaTarget, op::Union{Arr, ArrayOp}, args...;
+function _build_function(target::JuliaTarget, op::Union{Arr, ArrayOp, SymbolicUtils.BasicSymbolic{<:AbstractArray}}, args...;
                          conv = toexpr,
                          expression = Val{true},
                          expression_module = @__MODULE__(),
@@ -141,6 +141,7 @@ function _build_function(target::JuliaTarget, op::Union{Arr, ArrayOp}, args...;
                          linenumbers = true,
                          cse = false,
                          nanmath = true,
+                         wrap_code = (identity, identity),
                          kwargs...)
 
     dargs = map((x) -> destructure_arg(x[2], !checkbounds,
@@ -155,7 +156,7 @@ function _build_function(target::JuliaTarget, op::Union{Arr, ArrayOp}, args...;
 
     outsym = Symbol("ˍ₋out")
     body = inplace_expr(unwrap(op), outsym)
-    oop_expr = conv(Func([outsym, dargs...], [], body), states)
+    iip_expr = conv(wrap_code[2](Func([outsym, dargs...], [], body)), states)
 
     N = length(shape(op))
     op = unwrap(op)
@@ -167,18 +168,18 @@ function _build_function(target::JuliaTarget, op::Union{Arr, ArrayOp}, args...;
               $outsym
           end) |> LiteralExpr
     end
-    ip_expr = conv(Func(dargs, [], op_body), states)
+    oop_expr = conv(wrap_code[1](Func(dargs, [], op_body)), states)
     if !checkbounds
         @assert Meta.isexpr(oop_expr, :function)
         oop_expr.args[2] = :(@inbounds begin; $(oop_expr.args[2]); end)
-        @assert Meta.isexpr(ip_expr, :function)
-        ip_expr.args[2] = :(@inbounds begin; $(ip_expr.args[2]); end)
+        @assert Meta.isexpr(iip_expr, :function)
+        iip_expr.args[2] = :(@inbounds begin; $(iip_expr.args[2]); end)
     end
     if expression == Val{true}
-        oop_expr, ip_expr
+        oop_expr, iip_expr
     else
         _build_and_inject_function(expression_module, oop_expr),
-        _build_and_inject_function(expression_module, ip_expr)
+        _build_and_inject_function(expression_module, iip_expr)
     end
 end
 
diff --git a/test/build_function.jl b/test/build_function.jl
index 0c09fdd6d..f7df7b763 100644
--- a/test/build_function.jl
+++ b/test/build_function.jl
@@ -290,3 +290,14 @@ end
     fn = build_function(T, collect(x); similarto = Array, expression = false)[1]
     @test fn((1.0, 2.0)) ≈ [1.0, 4.0]
 end
+
+@testset "`build_function` with array symbolics" begin
+    @variables x[1:4]
+    for var in [x[1:2], x[1:2] .+ 0.0, Symbolics.unwrap(x[1:2])]
+        foop, fiip = build_function(var[1:2], x; expression = false)
+        @test foop(ones(4)) ≈ ones(2)
+        buf = zeros(2)
+        fiip(buf, ones(4))
+        @test buf ≈ ones(2)
+    end
+end