From 6fbeffde547e948bad166798192f6b59805163c6 Mon Sep 17 00:00:00 2001
From: Xianda Sun <5433119+sunxd3@users.noreply.github.com>
Date: Fri, 12 Apr 2024 11:57:21 +0100
Subject: [PATCH] Ignore `identity` optic when composing (#96)

---
 Project.toml    | 2 +-
 src/varname.jl  | 9 ++++++++-
 test/varname.jl | 7 +++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index f4f73c8..e929d94 100644
--- a/Project.toml
+++ b/Project.toml
@@ -3,7 +3,7 @@ uuid = "7a57a42e-76ec-4ea3-a279-07e840d6d9cf"
 keywords = ["probablistic programming"]
 license = "MIT"
 desc = "Common interfaces for probabilistic programming"
-version = "0.8.2"
+version = "0.8.3"
 
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"
diff --git a/src/varname.jl b/src/varname.jl
index 0f470a1..05d20b6 100644
--- a/src/varname.jl
+++ b/src/varname.jl
@@ -150,7 +150,14 @@ end
 
 # Allow compositions with optic.
 function Base.:∘(optic::ALLOWED_OPTICS, vn::VarName{sym,<:ALLOWED_OPTICS}) where {sym}
-    return VarName{sym}(optic ∘ getoptic(vn))
+    vn_optic = getoptic(vn)
+    if vn_optic == identity
+        return VarName{sym}(optic)
+    elseif optic == identity
+        return vn
+    else
+        return VarName{sym}(optic ∘ vn_optic)
+    end
 end
 
 Base.hash(vn::VarName, h::UInt) = hash((getsym(vn), getoptic(vn)), h)
diff --git a/test/varname.jl b/test/varname.jl
index a26e346..d0e3de7 100644
--- a/test/varname.jl
+++ b/test/varname.jl
@@ -53,6 +53,13 @@ end
     @testset "compose and opcompose" begin
         @test IndexLens(1) ∘ @varname(x.a) == @varname(x.a[1])
         @test @varname(x.a) ⨟ IndexLens(1) == @varname(x.a[1])
+
+        @test @varname(x) ⨟ identity == @varname(x)
+        @test identity ∘ @varname(x) == @varname(x)
+        @test @varname(x.a) ⨟ identity == @varname(x.a)
+        @test identity ∘ @varname(x.a) == @varname(x.a)
+        @test @varname(x[1].b) ⨟ identity == @varname(x[1].b)
+        @test identity ∘ @varname(x[1].b) == @varname(x[1].b)
     end
 
     @testset "get & set" begin