Low: qblist.h: fix incompatibility with C++ & check it regularly

Primary trigger was the fact that "./check abi" (via
build-aux/generate-docs) choked on that because abi-dumper,
likely since 0.99.16 (fead8fa) can/will use g++ to list symbols
in header files, which apparently applies C++ perspective there,
which likely was unprecedented even though libqb no doubt
targets such compatiblity.

To avoid its breakage within the public headers' scope in the future,
arrange for checking it regularly alongside the "auto_check_header"
tests (cf. make -C tests check-headers).

Signed-off-by: Jan Pokorný <[email protected]>

include/qb/qblist.h

@@ -109,16 +109,16 @@ static inline void qb_list_del(struct qb_list_head *_remove)
 
 /**
  * Replace old entry by new one
- * @param old: the element to be replaced
- * @param new: the new element to insert
+ * @param old_one: the element to be replaced
+ * @param new_one: the new element to insert
  */
-static inline void qb_list_replace(struct qb_list_head *old,
-		struct qb_list_head *new)
+static inline void qb_list_replace(struct qb_list_head *old_one,
+		struct qb_list_head *new_one)
 {
-	new->next = old->next;
-	new->next->prev = new;
-	new->prev = old->prev;
-	new->prev->next = new;
+	new_one->next = old_one->next;
+	new_one->next->prev = new_one;
+	new_one->prev = old_one->prev;
+	new_one->prev->next = new_one;
 }
 
 /**

tests/Makefile.am

@@ -78,7 +78,13 @@ check: check-headers
 
 # rely on implicit automake rule to include right (local) includes
 .PHONY: check-headers
-check-headers: $(auto_c_files:.c=.o)
+check-headers: $(auto_c_files:.c=.o) $(auto_c_files:.c=.opp)
+
+# this is to attest basic sanity for using libqb from C++ code when possible
+%.opp: %.c
+	@which $(CXX) >/dev/null || { echo '$<: cannot test C++ compat'; exit 0; }
+	$(AM_V_GEN)$(CXX) $(AM_CPPFLAGS) -c $(CPPFLAGS) $(CXXFLAGS) -o $@ $<
+CLEANFILES += ${auto_c_files:.c=.opp}
 
 distclean-compile:
 	rm -rf auto_*.c