Add optional parameter to PG_TRY() macros

This optional parameter can be specified in cases where there are nested
PG_TRY() statements within a function in order to stop the compiler from
issuing warnings about shadowed local variables when compiling with
-Wshadow.  The optional parameter is used as a suffix on the variable
names declared within the PG_TRY(), PG_CATCH(), PG_FINALLY() and
PG_END_TRY() macros.  The parameter, if specified, must be the same in
each component macro of the given PG_TRY() block.

This also adjusts the single case where we have nested PG_TRY() statements
to add a parameter to the inner-most PG_TRY().

This reduces the number of compiler warnings when compiling with
-Wshadow=compatible-local from 5 down to 1.

Author: David Rowley
Discussion: https://postgr.es/m/CAApHDvqWGMdB_pATeUqE=JCtNqNxObPOJ00jFEa2_sZ20j_Wvg@mail.gmail.com

Author: david-rowley

src/backend/tcop/utility.c

@@ -1678,16 +1678,16 @@ ProcessUtilitySlow(ParseState *pstate,
 				 * command itself is queued, which is enough.
 				 */
 				EventTriggerInhibitCommandCollection();
-				PG_TRY();
+				PG_TRY(2);
 				{
 					address = ExecRefreshMatView((RefreshMatViewStmt *) parsetree,
 												 queryString, params, qc);
 				}
-				PG_FINALLY();
+				PG_FINALLY(2);
 				{
 					EventTriggerUndoInhibitCommandCollection();
 				}
-				PG_END_TRY();
+				PG_END_TRY(2);
 				break;
 
 			case T_CreateTrigStmt:

src/include/utils/elog.h

@@ -310,39 +310,47 @@ extern PGDLLIMPORT ErrorContextCallback *error_context_stack;
  * pedantry; we have seen bugs from compilers improperly optimizing code
  * away when such a variable was not marked.  Beware that gcc's -Wclobbered
  * warnings are just about entirely useless for catching such oversights.
+ *
+ * Each of these macros accepts an optional argument which can be specified
+ * to apply a suffix to the variables declared within the macros.  This suffix
+ * can be used to avoid the compiler emitting warnings about shadowed
+ * variables when compiling with -Wshadow in situations where nested PG_TRY()
+ * statements are required.  The optional suffix may contain any character
+ * that's allowed in a variable name.  The suffix, if specified, must be the
+ * same within each component macro of the given PG_TRY() statement.
  *----------
  */
-#define PG_TRY()  \
+#define PG_TRY(...)  \
 	do { \
-		sigjmp_buf *_save_exception_stack = PG_exception_stack; \
-		ErrorContextCallback *_save_context_stack = error_context_stack; \
-		sigjmp_buf _local_sigjmp_buf; \
-		bool _do_rethrow = false; \
-		if (sigsetjmp(_local_sigjmp_buf, 0) == 0) \
+		sigjmp_buf *_save_exception_stack##__VA_ARGS__ = PG_exception_stack; \
+		ErrorContextCallback *_save_context_stack##__VA_ARGS__ = error_context_stack; \
+		sigjmp_buf _local_sigjmp_buf##__VA_ARGS__; \
+		bool _do_rethrow##__VA_ARGS__ = false; \
+		if (sigsetjmp(_local_sigjmp_buf##__VA_ARGS__, 0) == 0) \
 		{ \
-			PG_exception_stack = &_local_sigjmp_buf
+			PG_exception_stack = &_local_sigjmp_buf##__VA_ARGS__
 
-#define PG_CATCH()	\
+#define PG_CATCH(...)	\
 		} \
 		else \
 		{ \
-			PG_exception_stack = _save_exception_stack; \
-			error_context_stack = _save_context_stack
+			PG_exception_stack = _save_exception_stack##__VA_ARGS__; \
+			error_context_stack = _save_context_stack##__VA_ARGS__
 
-#define PG_FINALLY() \
+#define PG_FINALLY(...) \
 		} \
 		else \
-			_do_rethrow = true; \
+			_do_rethrow##__VA_ARGS__ = true; \
 		{ \
-			PG_exception_stack = _save_exception_stack; \
-			error_context_stack = _save_context_stack
+			PG_exception_stack = _save_exception_stack##__VA_ARGS__; \
+			error_context_stack = _save_context_stack##__VA_ARGS__
 
-#define PG_END_TRY()  \
+#define PG_END_TRY(...)  \
 		} \
-		if (_do_rethrow) \
+		if (_do_rethrow##__VA_ARGS__) \
 				PG_RE_THROW(); \
-		PG_exception_stack = _save_exception_stack; \
-		error_context_stack = _save_context_stack; \
+		PG_exception_stack = _save_exception_stack##__VA_ARGS__; \
+		error_context_stack = _save_context_stack##__VA_ARGS__; \
 	} while (0)
 
 /*