use --add-tracefile option to handle duplicate SF in coverage.info (sonic-net#3482)

What I did
use --add-tracefile option in debian/rules and tests/conftest.py to sanitize coverage.info generated by lcov

Why I did it
lcov generates an initial coverage.info file based on collected .gcno and .gcda files, this .info file contains coverage information for different source files (marked as SF). Sometimes you would observe that the same SF appears multiple times, it means lcov gets multiple copies of coverage information for this file, since this file may have appeared in multiple compilation units, and for each copy, the hit times of its lines are different.

Then lcov_cobertura generates coverage.xml based on coverage.info. However, it can't deal with duplicate SF in coverage.info properly. If it sees duplicate coverage information for a source file from coverage.info, it always overwrites the old copy with the new copy, hence only the last copy would be counted. However, if the last copy considers the functions as missing, the function is considered as missing in coverage.xml, which is used to determine whether the new PR passes the coverage threshold.

The proper way is to add the hit times of all the copies, which could be achieved by lcov add-tracefile option.

Author: a114j0y

debian/rules

@@ -44,6 +44,7 @@ override_dh_auto_install:
 ifeq ($(ENABLE_GCOV), y)
 	mkdir -p debian/swss/tmp/gcov
 	lcov -c --directory . --no-external --exclude "$(shell pwd)/tests/*" --exclude "$(shell pwd)/**/tests/*" --ignore-errors gcov --output-file coverage.info
+	lcov --add-tracefile coverage.info -o coverage.info
 	lcov_cobertura coverage.info -o coverage.xml
 	find ./ -type f -regex '.*\.\(h\|cpp\|gcno\|info\)' | tar -cf debian/swss/tmp/gcov/gcov-source.tar -T -
 endif

tests/conftest.py

@@ -462,7 +462,7 @@ def collect_coverage(self):
                 self.runcmd('supervisorctl stop all')
 
             # Generate the converage info by lcov and copy to the host
-            cmd = f"docker exec {self.ctn.short_id} sh -c 'cd $BUILD_DIR; rm -rf **/.libs ./lib/libSaiRedis*; lcov -c --directory . --no-external --exclude tests --ignore-errors gcov,unused --output-file /tmp/coverage.info; sed -i \"s#SF:$BUILD_DIR/#SF:#\" /tmp/coverage.info; lcov_cobertura /tmp/coverage.info -o /tmp/coverage.xml'"
+            cmd = f"docker exec {self.ctn.short_id} sh -c 'cd $BUILD_DIR; rm -rf **/.libs ./lib/libSaiRedis*; lcov -c --directory . --no-external --exclude tests --ignore-errors gcov,unused --output-file /tmp/coverage.info && lcov --add-tracefile /tmp/coverage.info -o /tmp/coverage.info; sed -i \"s#SF:$BUILD_DIR/#SF:#\" /tmp/coverage.info; lcov_cobertura /tmp/coverage.info -o /tmp/coverage.xml'"
             subprocess.getstatusoutput(cmd)
             cmd = f"docker exec {self.ctn.short_id} sh -c 'cd $BUILD_DIR; find . -name *.gcda -type f   -exec tar -rf /tmp/gcda.tar {{}} \\;'"
             subprocess.getstatusoutput(cmd)