invariant_booleans

Conditions should not unconditionally evaluate to true or to false.

NOTE: This rule is removed in Dart 3.0.0; it is no longer functional.

DON'T test for conditions that can be inferred at compile time or test the same condition twice.

Conditional statements using a condition which cannot be anything but false have the effect of making blocks of code non-functional. If the condition cannot evaluate to anything but true, the conditional statement is completely redundant, and makes the code less readable. It is quite likely that the code does not match the programmer's intent. Either the condition should be removed or it should be updated so that it does not always evaluate to true or false and does not perform redundant tests. This rule will hint to the test conflicting with the linted one.

BAD:

// foo can't be both equal and not equal to bar in the same expression
if(foo == bar && something && foo != bar) {...}

BAD:

void compute(int foo) {
  if (foo == 4) {
    doSomething();
    // we know foo is equal to 4 at this point, so the next condition is always false
    if (foo > 4) {...}
    ...
  }
  ...
}

BAD:

void compute(bool foo) {
  if (foo) {
    return;
  }
  doSomething();
  // foo is always false here
  if (foo){...}
  ...
}

GOOD:

void nestedOK() {
  if (foo == bar) {
    foo = baz;
    if (foo != bar) {...}
  }
}

GOOD:

void nestedOk2() {
  if (foo == bar) {
    return;
  }
​
  foo = baz;
  if (foo == bar) {...} // OK
}

GOOD:

void nestedOk5() {
  if (foo != null) {
    if (bar != null) {
      return;
    }
  }
​
  if (bar != null) {...} // OK
}

To enable the invariant_booleans rule, add invariant_booleans under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - invariant_booleans

If you're instead using the YAML map syntax to configure linter rules, add invariant_booleans: true under linter > rules:

linter:
  rules:
    invariant_booleans: true