Find Logic Errors

Logic Error Detection

Analyze PHP code for logic errors that cause incorrect behavior.

Detection Patterns

1. Incorrect Comparison Operators

// BUG: Assignment instead of comparison
if ($status = 'active') { } // Should be ===

// BUG: Wrong comparison type
if ($count == '0') { } // 0, 0.0, '', null and false all match — use === '0'

// BUG: Yoda condition error
if ('active' = $status) { } // Assignment error

2. Inverted Logic

// BUG: Double negation confusion
if (!$user->isNotActive()) { } // Hard to reason about

// BUG: Wrong negation placement
if (!$a && $b) { } // vs if (!($a && $b))

// BUG: DeMorgan's law violation
if (!$a || !$b) { } // When meaning !($a && $b)

3. Missing Switch/Match Cases

// BUG: Missing enum case
match ($status) {
    Status::Active => 'active',
    Status::Inactive => 'inactive',
    // Missing: Status::Pending, Status::Deleted
};

// BUG: Missing default
switch ($type) {
    case 'A': return 1;
    case 'B': return 2;
    // No default - undefined behavior for other values
}

4. Short-Circuit Evaluation Issues

// BUG: Side effect in short-circuit
if ($valid && $this->save()) { } // save() not called if !$valid

// BUG: Order matters
if ($obj->method() && $obj !== null) { } // Null check too late

5. Off-by-One in Comparisons

// BUG: Fence post error
if ($index < count($array)) { } // vs <=

// BUG: Wrong boundary
for ($i = 0; $i <= $length; $i++) { } // Off by one

6. Boolean Expression Errors

// BUG: Always true/false
if ($age > 0 || $age <= 0) { } // Always true

// BUG: Unreachable condition
if ($x > 10 && $x < 5) { } // Always false

// BUG: Redundant condition
if ($status === 'active' && $status !== 'inactive') { } // Second part redundant

7. Return Value Ignorance

// BUG: Ignoring important return
array_push($items, $new); // Returns count, not array
$result = trim($string);  // trim() returns a new string; calling it without
                          // assigning discards the result
                          // (note: $string->trim() is a fatal error — PHP strings
                          //  are not objects and have no methods)

Grep Patterns

# Assignment in condition
Grep: "if\s*\([^=]*[^!=<>]=[^=][^)]*\)" --glob "**/*.php"

# Double negation
Grep: "!\$\w+->isNot|!!\$" --glob "**/*.php"

# Empty switch without default
Grep: "switch\s*\([^)]+\)\s*\{[^}]*\}" --glob "**/*.php"

Output Format

### Logic Error: [Description]

**Severity:** 🔴/🟠/🟡
**Location:** `file.php:line`
**Type:** [Incorrect Operator|Inverted Logic|Missing Case|...]

**Issue:**
[Description]

**Code:**
```php
// Current code

Fix:

// Corrected code