[apex] False positive with IfElseStmtsMustUseBraces

[rsoffiatto]

Affects PMD Version:
6.41.0+
7.0.0

Rule: IfElseStmtsMustUseBraces
https://pmd.github.io/pmd-6.41.0/pmd_rules_apex_codestyle.html#ifelsestmtsmustusebraces

Description:
PMD provides some rules for finding blocks without braces for Apex. Talking about ifs, it provides different rules for ifs with and without elses. But the rule made to only match if...elses are catching ifs without elses. Even the provided example for the rule states that it will not match an if without an else, but that is not what is happening now.

The problem is on the xpath used for catching the violation. If we use the provided one:

//IfBlockStatement/BlockStatement[@CurlyBrace= false()][count(child::*) > 0]
|
//IfElseBlockStatement/BlockStatement[@CurlyBrace= false()][count(child::*) > 0]

There is not an enforcement that the else must be present. We need something like:

//IfElseBlockStatement[@ElseStatement=true()]/IfBlockStatement/BlockStatement[@CurlyBrace= false()][count(child::*) > 0]
|
//IfElseBlockStatement[@ElseStatement=true()]/BlockStatement[@CurlyBrace= false()][count(child::*) > 0]

Where we make sure that the there is an else statement present.

Code Sample demonstrating the issue:
The example provided with the rule can be used to demonstrate the problem:

// this is OK
if (foo) x++;

// but this is not
if (foo)
    x = x+1;
else
    x = x-1;

Expected outcome:
PMD reports violations on lines 2, 6 and 8. But the violation on line 2 is wrong. Only the lines 6 and 8 should be reported

Running PMD through: CLI

[oowekyala]

Since you already have a fix, you could submit a PR. We'll gladly help if you have trouble

Side note: in the future, it would be nice to have an Apex rule similar to the Java ControlStatementBraces, which was added to merge all rules about braces and avoid this kind of mishaps.