fix dif:vars_remove_goal/2 (#2175), untabify forms.rs to appease format check

src/forms.rs

@@ -744,11 +744,11 @@ impl Number {
             Number::Float(f) => Number::Float(OrderedFloat(f.signum())),
             _ => {
                 if self.is_positive() {
-		    if self.is_zero() {
-			Number::Fixnum(Fixnum::build_with(0))
-		    } else {
-			Number::Fixnum(Fixnum::build_with(1))
-		    }
+                    if self.is_zero() {
+                        Number::Fixnum(Fixnum::build_with(0))
+                    } else {
+                        Number::Fixnum(Fixnum::build_with(1))
+                    }
                 } else if self.is_negative() {
                     Number::Fixnum(Fixnum::build_with(-1))
                 } else {

src/lib/dif.pl

@@ -33,11 +33,13 @@ remove_goal([G0|G0s], Goal0, Goals) :-
 
 vars_remove_goal([], _).
 vars_remove_goal([Var|Vars], Goal0) :-
-    get_atts(Var, +dif(Goals0)),
-    remove_goal(Goals0, Goal0, Goals),
-    (   Goals = [] ->
-        put_atts(Var, -dif(_))
-    ;   put_atts(Var, +dif(Goals))
+    (  get_atts(Var, +dif(Goals0)) ->
+       remove_goal(Goals0, Goal0, Goals),
+       (   Goals = [] ->
+           put_atts(Var, -dif(_))
+       ;   put_atts(Var, +dif(Goals))
+       )
+    ;  true
     ),
     vars_remove_goal(Vars, Goal0).
 

src/tests/dif.pl

@@ -207,6 +207,13 @@ test("scryer-prolog#2056",(
     \+ E=[]
 )).
 
+% https://github.com/mthom/scryer-prolog/issues/2175
+test("scryer-prolog#2175",(
+    dif(A,B),
+    A=_C*[],
+    A=[]*D*B,D=[]
+)).
+
 main :-
     findall(test(Name, Goal), test(Name, Goal), Tests),
     run_tests(Tests, Failed),