Adjust DatumGetBool macro, this time for sure.

tglsfdc · tglsfdc · commit 65c2eeb003bf · 2016-04-28T11:51:13.000-04:00
Commit 23a4157 attempted to fix the DatumGetBool macro to ignore bits in a Datum that are to the left of the actual bool value. But it did that by casting the Datum to bool; and on compilers that use C99 semantics for bool, that ends up being a whole-word test, not a 1-byte test. This seems to be the true explanation for contrib/seg failing in VS2015. To fix, use GET_1_BYTE() explicitly. I think in the previous patch, I'd had some idea of not having to commit to bool being exactly 1 byte wide, but regardless of what the compiler's bool is, boolean columns and Datums are certainly 1 byte wide. The previous fix was (eventually) back-patched into all active versions, so do likewise with this one.
diff --git a/src/include/postgres.h b/src/include/postgres.h
@@ -368,7 +368,7 @@ typedef Datum *DatumPtr;
  * the left of the width of bool, per comment above.
  */
 
-#define DatumGetBool(X) ((bool) (((bool) (X)) != 0))
+#define DatumGetBool(X) ((bool) (GET_1_BYTE(X) != 0))
 
 /*
  * BoolGetDatum
