don't append " ∘ (@o _)" in show_optic

show_optic is not a public API, but convenient to use sometimes
before, it appended  " ∘ (@o _)" unnecessarily for objects that don't have explicit show_optic handling

Author: aplavin

src/sugar.jl

@@ -521,19 +521,23 @@ function show_optic(io, optic)
     outer = Iterators.dropwhile(x -> applicable(_shortstring, "", x), opts)
     if !isempty(outer)
         show(io, opcompose(outer...))
+    end
+    if !isempty(inner) && !isempty(outer)
         print(io, " ∘ ")
     end
-    shortstr = reduce(inner; init=("_", false)) do (prev, need_parens_prev), o
-        # if _need_parens is true for this o and the one before, wrap the previous one in parentheses
-        if need_parens_prev && _need_parens(o)
-            prev = "($prev)"
+    if !isempty(inner)
+        shortstr = reduce(inner; init=("_", false)) do (prev, need_parens_prev), o
+            # if _need_parens is true for this o and the one before, wrap the previous one in parentheses
+            if need_parens_prev && _need_parens(o)
+                prev = "($prev)"
+            end
+            _shortstring(prev, o), _need_parens(o)
+        end |> first
+        if get(io, :compact, false)
+            print(io, shortstr)
+        else
+            print(io, "(@o ", shortstr, ")")
         end
-        _shortstring(prev, o), _need_parens(o)
-    end |> first
-    if get(io, :compact, false)
-        print(io, shortstr)
-    else
-        print(io, "(@o ", shortstr, ")")
     end
 end
 

test/test_core.jl

@@ -470,6 +470,11 @@ end
     @test sprint(show, (@optic log(_.a[2])); context=:compact => true) == "log(_.a[2])"
     @test sprint(show, (@optic Base.tail(_.a[2])); context=:compact => true) == "tail(_.a[2])"  # non-exported function
     @test sprint(show, (@optic Base.Fix2(_.a[2])); context=:compact => true) == "Fix2(_.a[2])"  # non-exported type
+
+    # show_optic is reasonable even for types without special show_optic handling:
+    o = Recursive(x->true, Properties())
+    @test sprint(Accessors.show_optic, o) == "$o"
+    @test sprint(Accessors.show_optic, (@o _.a) ∘ o) == "(@o _.a) ∘ $o"
 end
 
 @testset "text/plain show" begin