feat: support Symbolics@7

Project.toml

@@ -27,6 +27,6 @@ MacroTools = "0.5"
 NNlib = "0.9"
 SpecialFunctions = "2"
 SymbolicUtils = "3, 4"
-Symbolics = "6"
+Symbolics = "6, 7"
 Zygote = "0.6, 0.7"
 julia = "1.10"

src/utils.jl

@@ -4,6 +4,7 @@
 using ChainRules
 using ChainRulesCore
 using Symbolics: Symbolics, @variables, @rule, unwrap, isdiv
+import SymbolicUtils
 using SymbolicUtils.Code: toexpr
 using MacroTools
 using MacroTools: prewalk, postwalk
@@ -13,19 +14,58 @@ Pick a strategy for raising the derivative of a function.
 If the derivative is like 1 over something, raise with the division rule;
 otherwise, raise with the multiplication rule.
 """
-function get_term_raiser(func)
-    @variables z
-    r1 = @rule -1 * (1 / ~x) => (-1) / ~x
-    der = frule((NoTangent(), true), func, z)[2]
-    term = unwrap(der)
-    maybe_rewrite = r1(term)
-    if maybe_rewrite !== nothing
-        term = maybe_rewrite
+function get_term_raiser end
+
+@static if pkgversion(Symbolics) < v"7"
+  function get_term_raiser(func)
+      @variables z
+      r1 = @rule -1 * (1 / ~x) => (-1) / ~x
+      der = frule((NoTangent(), true), func, z)[2]
+      term = unwrap(der)
+      maybe_rewrite = r1(term)
+      if maybe_rewrite !== nothing
+          term = maybe_rewrite
+      end
+      if isdiv(term) && (term.num == 1 || term.num == -1)
+          term.den * term.num, raiseinv
+      else
+          term, raise
+      end
+  end
+else
+    const COMMON_Z = only(@variables z)
+    const FALLBACK_RULE = (@rule -1 * (1 / ~x) => (-1) / ~x)
+
+    function is_plusminus_one(@nospecialize(x))
+        if x isa Int
+            return x == 1 || x == -1
+        elseif x isa Int32
+            return x == 1 || x == -1
+        elseif x isa Float64
+            return x == 1 || x == -1
+        elseif x isa Float32
+            return x == 1 || x == -1
+        elseif x isa Number
+            return (x == 1)::Bool || (x == -1)::Bool
+        else
+            return false
+        end
     end
-    if isdiv(term) && (term.num == 1 || term.num == -1)
-        term.den * term.num, raiseinv
-    else
-        term, raise
+
+    function get_term_raiser(func)
+        der = frule((NoTangent(), true), func, COMMON_Z)[2]
+        term = unwrap(der)
+        maybe_rewrite = FALLBACK_RULE(term)
+        if maybe_rewrite !== nothing
+            term = maybe_rewrite
+        end
+        if isdiv(term)
+            num, den = SymbolicUtils.arguments(term)
+            if SymbolicUtils.isconst(num) && is_plusminus_one(SymbolicUtils.unwrap_const(num))
+                return num * den, raiseinv
+            end
+        end
+        return term, raise
     end
 end