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Many Lints

avoid_unnecessary_negations

v0.8.0 Warning Fix Control Flow

This rule flags a negation that can be removed without changing the meaning. Four shapes are reported.

Don’t

Section titled “Don’t”

A negation over a negation. Usually the result of inverting a condition and leaving the inner expression as it was:

void start() {}


void toggle(bool isEnabled) {
  if (!!isEnabled) {
    start();
  }
}

A negation over !=. The ! and the != cancel:

enum Status { active, archived }


void activate() {}


void refresh(Status status) {
  if (!(status != Status.active)) {
    activate();
  }
}

A negation over a boolean literal. !true is just false written the long way — most often a feature flag that was flipped in place:

void renderLegacyBanner() {}


void render() {
  if (!true) {
    renderLegacyBanner();
  }
}

A negation on both sides of a comparison. Negating both operands leaves the answer unchanged:

void sync() {}


void check(bool isReady, bool isLoaded) {
  if (!isReady == !isLoaded) {
    sync();
  }
}

Do

Section titled “Do”

The quick fix removes the redundant operators, one diagnostic at a time:

enum Status { active, archived }


void start() {}
void activate() {}
void renderLegacyBanner() {}
void sync() {}


void examples(bool isEnabled, Status status, bool isReady, bool isLoaded) {
  if (isEnabled) {
    start();
  }


  if (status == Status.active) {
    activate();
  }


  if (false) {
    renderLegacyBanner();
  }


  if (isReady == isLoaded) {
    sync();
  }
}

Known limitations

Section titled “Known limitations”

Four shapes are reported: ! applied to a ! expression, ! applied to a != comparison, ! applied to a boolean literal, and ==/!= with a negation on both sides. Parentheses are unwrapped first, so !(!flag) is caught.

A single negation in a comparison (!a == b) is left alone — removing it would change the result. A negated == (!(a == b)) is also deliberately excluded: it is a single negation, and rewriting it to != is a style preference rather than a redundancy. Negated relational comparisons are handled by avoid_inverted_boolean_checks instead, so the same code is never reported twice.

Configuration

Section titled “Configuration”

This rule is in the core preset, so it is on with preset: core, preset: recommended or preset: opinionated.

To turn it off:

many_lints.yaml
rules:
  avoid_unnecessary_negations: false

To keep the rule on but skip certain paths, use per-rule exclude.

Section titled “Related rules”