Analysis Details

Do Not Attempt to Help the Garbage Collector by Setting Local Reference Variables to Null

es.uniovi.reflection.analyses.cmu.obj54

This rule detects the assignment of null to local variables that are no longer used.

Computational Reflection Research Group

05-08-2024 22:58

Programmer Misconceptions

Assignment

MATCH (varDec:LOCAL_DEF)-[:MODIFIED_BY]->(ass:ASSIGNMENT)-[:ASSIGNMENT_RHS]->(:LITERAL{typeKind:'NULL'})
WITH DISTINCT varDec, es.uniovi.reflection.codeanalysis.functions.getEnclosingStmt(ass) as assStat 
OPTIONAL MATCH (varDec)-[:USED_BY | STATE_MODIFIED_BY]->(useExpr:EXPRESSION)
WHERE NOT useExpr:CALL WITH varDec, assStat, COLLECT( DISTINCT es.uniovi.reflection.codeanalysis.functions.getEnclosingStmt(useExpr)) as useStats
CALL apoc.path.subgraphNodes(assStat, {terminatorNodes:useStats, limit:1, minLevel:0, optional:true, relationshipFilter:'CFG_NEXT_STATEMENT>|CFG_NEXT_STATEMENT_IF_TRUE>|CFG_NEXT_STATEMENT_IF_FALSE>|CFG_FOR_EACH_HAS_NEXT>|CFG_FOR_EACH_NO_MORE_ELEMENTS>|CFG_NO_EXCEPTION>|CFG_CAUGHT_EXCEPTION>|CFG_AFTER_FINALLY_PREVIOUS_BREAK>|CFG_AFTER_FINALLY_PREVIOUS_CONTINUE>|CFG_SWITCH_CASE_IS_EQUAL_TO>|CFG_SWITCH_DEFAULT_CASE>|CFG_IF_THERE_IS_UNCAUGHT_EXCEPTION>|CFG_MAY_THROW>|CFG_THROWS>|TRY_CATCH>'}) yield node
WHERE node IS NULL
WITH DISTINCT varDec, assStat, es.uniovi.reflection.codeanalysis.functions.getEnclosingMethod(varDec) as varMember 
MATCH (varMember)<-[:DECLARES_METHOD | DECLARES_CONSTRUCTOR | HAS_STATIC_INIT]-(enclClass)<-[:HAS_TYPE_DEF | HAS_INNER_TYPE_DEF]-(cu:COMPILATION_UNIT)
RETURN '{"rule":"CMU-OBJ54","location":"' + cu.fileName + '","node":"EXPRESSION","line":"' + assStat.lineNumber + '","column":"' + assStat.column + '","message":"You must not try to help garbage collector setting references to null when they are no longer used. To make your code clearer, just delete the assignment in line ' + assStat.lineNumber + ' of the variable ' + varDec.name + ' declared in line ' + varDec.lineNumber + ',class ' + enclClass.fullyQualifiedName + '"}'