Merge pull request #1673 from wilzbach/deprecate-enum-comparison

Deprecation: Issue 6227 - Comparison of different enums
merged-on-behalf-of: Vladimir Panteleev <github@thecybershadow.net>

Author: dlang-bot

deprecate.dd

@@ -10,6 +10,7 @@ $(SPEC_S Deprecated Features,
 
     $(TABLE2 Deprecated Features,
         $(THEAD Feature,                                                          Spec,  Dep,    Error,  Gone)
+        $(TROW $(DEPLINK Implicit comparison of different enums),                 2.075,  2.075,  ,  )
         $(TROW $(DEPLINK Implicit string concatenation),                          2.072,  2.072,  ,  )
         $(TROW $(DEPLINK Using the result of a comma expression),                 2.072,  2.072,   ,  )
         $(TROW $(DEPLINK delete),                                                 future,  ,  ,  )
@@ -57,16 +58,51 @@ $(SPEC_S Deprecated Features,
         $(DD The feature is completely gone)
     )
 
+$(H3 $(DEPNAME Implicit comparison of different enums))
+    $(P Comparison of different enumerated type was allowed:
+        ---
+        enum Status
+        {
+            good,
+            bad
+        }
+        enum OtherStatus
+        {
+            ok
+            no,
+        }
+        static assert(Status.good == OtherStatus.ok);
+        ---
+    )
+$(H4 Corrective Action)
+    $(P Comparison between unrelated enumerated types should be done with $(REF asOriginalType, std, conv))
+        ---
+        import std.conv : asOriginalType;
+        assert(Foo.x.asOriginalType == Bar.y.asOriginalType);
+        ---
+$(H4 Rationale)
+    $(P Code correctness is improved by
+        disallowing comparison of unrelated enumerated types. Implicit comparison of
+        different `enum` types often resulted in hard to spot bugs.)
+
+        ---
+        enum { X }
+        enum { Y }
+        void main() {
+            auto b = X == Y;
+            assert(b);
+        }
+        ---
 
 $(H3 $(DEPNAME Implicit string concatenation))
-    $(P Currently, two adjacent strings are implicitly concatenated:
+    $(P Two adjacent strings were implicitly concatenated:
 
         ---
         string foo = "Hello" "World";
         ---
 
-        This feature is handy for a long string that spans multiple lines,
-        however it is possible to get the same behaviour explicitly by
+        This feature was handy for a long string that spans multiple lines,
+        however, it is possible to get the same behaviour explicitly by
         using the concatenation operator ('~'):
 
         ---