[cfe-commits] [Patch] Add a warning to catch enums with all elements having the same value

[Douglas Gregor]

On May 15, 2012, at 4:10 PM, Richard Trieu <rtrieu at google.com> wrote:

> Add -Wunique-enum which will warn on enums with at least 2 elements such that all elements are the same value.  This will catch enums such as:
> 
> enum A {
>   FIRST = 1,
>   SECOND = 1
> };

Why do we need this warning? Personally, I can't recall having seen this be the source of any bugs, and it's scope is so narrow that it doesn't seem worth adding.

As for the actual patch…

+def warn_identical_enum_values : Warning<
+  "all elements of %select{anonymous enum|%1}0 have value %2">,
+  InGroup<DiagGroup<"unique-enum">>, DefaultIgnore;
+

Default-ignore warnings are always a red flag. If this warning is important, it should be on by default. If it's not important, we shouldn't add it.

+  // Keep track of whther all the elements have the same value.
+  bool AllElementsEqual = true;
+  llvm::APSInt LastVal;

Typo "whther".

+    // Keep track of whether every enum element is the same value.
+    if (AllElementsEqual && i > 0) {
+      if (InitVal.getBitWidth() > LastVal.getBitWidth())
+        AllElementsEqual = InitVal == LastVal.extend(InitVal.getBitWidth());
+      else if (InitVal.getBitWidth() < LastVal.getBitWidth())
+        AllElementsEqual = InitVal.extend(LastVal.getBitWidth()) == LastVal;
+      else
+        AllElementsEqual = InitVal == LastVal;
+    }
+    LastVal = InitVal;
+

If you did this in the loop below, where we adjust the initializer values to all have the same size/# of bits, it would be easier.

	- Doug