# redundant-existence-check

**Summary**: Redundant existence check

**Category**: Bugs

**Automatically fixable**: [Yes](https://www.openpolicyagent.org/projects/regal/fixing)

**Avoid**

```
package policyemployee if {    input.user.email    endswith(input.user.email, "@acmecorp.com")}is_admin(user) if {    user    "admin" in user.roles}
```

**Prefer**

```
package policyemployee if {    endswith(input.user.email, "@acmecorp.com")}# alternativelyemployee if endswith(input.user.email, "@acmecorp.com")is_admin(user) if {    "admin" in user.roles}
```

## Rationale

Checking that a reference (like `input.user.email`) is defined before immediately using it is redundant. If the reference is undefined, the next expression will fail anyway, as the value will be checked before the rest of the expression is evaluated. While an extra check doesn't "hurt", it also serves no purpose, similarly to an unused variable.

**Note**: This rule only applies to references that are immediately used in the next expression. If the reference is used later in the rule, it won't be flagged. While the existence check _could_ be redundant even in that case, it could also be used to avoid making some expensive computation, an `http.send` call, or whatnot.

## Exceptions

Function arguments where a boolean value is expected will be flagged as redundant existence checks, even though the intent was to check the boolean condition.

```
report(user, is_admin) if {    is_admin    # more conditions}
```

For these cases, prefer to be explicit about what the assertion is checking:

```
report(user, is_admin) if {    is_admin == false # or true, != false, etc.    # more conditions}
```

## Configuration Options

This linter rule provides the following configuration options:

```
rules:  bugs:    redundant-existence-check:      # one of "error", "warning", "ignore"      level: error
```

## Related Resources

*   GitHub: [Source Code](https://github.com/open-policy-agent/regal/blob/main/bundle/regal/rules/bugs/redundant-existence-check/redundant_existence_check.rego)