clang-tidy - bugprone-redundant-branch-condition — Extra Clang Tools 12 documentation

# Extra Clang Tools 12 documentation

## clang-tidy - bugprone-redundant-branch-condition

# bugprone-redundant-branch-condition

Finds condition variables in nested `if` statements that were also checked in the outer `if` statement and were not changed.

Simple example:

    bool onFire = isBurning();
    if (onFire) {
      if (onFire)
        scream();
    }

Here onFire is checked both in the outer `if` and the inner `if` statement without a possible change between the two checks. The check warns for this code and suggests removal of the second checking of variable onFire.

The checker also detects redundant condition checks if the condition variable is an operand of a logical “and” (`&&`) or a logical “or” (`||`) operator:

    bool onFire = isBurning();
    if (onFire) {
      if (onFire && peopleInTheBuilding > 0)
        scream();
    }

    bool onFire = isBurning();
    if (onFire) {
      if (onFire || isCollapsing())
        scream();
    }

In the first case (logical “and”) the suggested fix is to remove the redundant condition variable and keep the other side of the `&&`. In the second case (logical “or”) the whole `if` is removed similarily to the simple case on the top.

The condition of the outer `if` statement may also be a logical “and” (`&&`) expression:

    bool onFire = isBurning();
    if (onFire && fireFighters < 10) {
      if (someOtherCondition()) {
        if (onFire)
          scream();
      }
    }

The error is also detected if both the outer statement is a logical “and” (`&&`) and the inner statement is a logical “and” (`&&`) or “or” (`||`). The inner `if` statement does not have to be a direct descendant of the outer one.

No error is detected if the condition variable may have been changed between the two checks:

    bool onFire = isBurning();
    if (onFire) {
      tryToExtinguish(onFire);
      if (onFire && peopleInTheBuilding > 0)
        scream();
    }

Every possible change is considered, thus if the condition variable is not a local variable of the function, it is a volatile or it has an alias (pointer or reference) then no warning is issued.

## Known limitations

The `else` branch is not checked currently for negated condition variable:

    bool onFire = isBurning();
    if (onFire) {
      scream();
    } else {
      if (!onFire) {
        continueWork();
      }
    }

The checker currently only detects redundant checking of single condition variables. More complex expressions are not checked:

    if (peopleInTheBuilding == 1) {
      if (peopleInTheBuilding == 1) {
        doSomething();
      }
    }