Improve decimal cast fix

src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php

@@ -31,6 +31,7 @@
 use ReflectionClass;
 use ReflectionMethod;
 use ReflectionNamedType;
+use RuntimeException;
 use TypeError;
 
 trait HasAttributes
@@ -1313,21 +1314,27 @@ public function fromFloat($value)
     /**
      * Return a decimal as string.
      *
-     * @param  float  $value
+     * @param  float|string  $value
      * @param  int  $decimals
      * @return string
      */
     protected function asDecimal($value, $decimals)
     {
-        $value = (string) $value;
+        if (extension_loaded('bcmath')) {
+            return bcadd($value, 0, $decimals);
+        }
 
         if (! is_numeric($value)) {
             throw new TypeError('$value must be numeric.');
         }
 
+        if (is_string($value) && Str::contains($value, 'e', true)) {
+            throw new RuntimeException('The "decimal" model cast is unable to handle string based floats with exponents.');
+        }
+
         [$int, $fraction] = explode('.', $value) + [1 => ''];
 
-        return $int.'.'.Str::of($fraction)->limit($decimals, '')->padLeft($decimals, '0');
+        return Str::of($int)->padLeft('1', '0').'.'.Str::of($fraction)->limit($decimals, '')->padRight($decimals, '0');
     }
 
     /**

tests/Integration/Database/EloquentModelDecimalCastingTest.php

@@ -7,6 +7,7 @@
 use Illuminate\Support\Facades\Schema;
 use Illuminate\Tests\Integration\Database\DatabaseTestCase;
 use TypeError;
+use ValueError;
 
 class EloquentModelDecimalCastingTest extends DatabaseTestCase
 {
@@ -19,6 +20,59 @@ protected function defineDatabaseMigrationsAfterDatabaseRefreshed()
         });
     }
 
+    public function testItHandlesExponent()
+    {
+        $model = new class extends Model
+        {
+            public $timestamps = false;
+
+            protected $casts = [
+                'amount' => 'decimal:20',
+            ];
+        };
+
+        $model->amount = 0.123456789e3;
+        $this->assertSame('123.45678900000000000000', $model->amount);
+    }
+
+    public function testItThrowsWhenPassingExponentAsString()
+    {
+        $model = new class extends Model
+        {
+            public $timestamps = false;
+
+            protected $casts = [
+                'amount' => 'decimal:20',
+            ];
+        };
+        $model->amount = '0.1e3';
+
+        if (extension_loaded('bcmath')) {
+            $this->expectException(ValueError::class);
+        } else {
+            $this->expectException(RuntimeException::class);
+            $this->expectExceptionMessage('The "decimal" model cast is unable to handle string based floats with exponents.'); // when bcmath is not available
+
+        }
+
+        $model->amount;
+    }
+
+    public function testItHandlesIntegersWithUnderscores()
+    {
+        $model = new class extends Model
+        {
+            public $timestamps = false;
+
+            protected $casts = [
+                'amount' => 'decimal:2',
+            ];
+        };
+
+        $model->amount = 1_234.5;
+        $this->assertSame('1234.50', $model->amount);
+    }
+
     public function testItThrowsOnNonNumericValues()
     {
         $model = new class extends Model
@@ -31,11 +85,33 @@ public function testItThrowsOnNonNumericValues()
         };
         $model->amount = 'foo';
 
-        $this->expectException(TypeError::class);
+        if (extension_loaded('bcmath')) {
+            $this->expectException(ValueError::class);
+        } else {
+            $this->expectException(TypeError::class);
+        }
 
         $model->amount;
     }
 
+    public function testItHandlesMissingIntegers()
+    {
+        $model = new class extends Model
+        {
+            public $timestamps = false;
+
+            protected $casts = [
+                'amount' => 'decimal:2',
+            ];
+        };
+
+        $model->amount = .8;
+        $this->assertSame('0.80', $model->amount);
+
+        $model->amount = '.8';
+        $this->assertSame('0.80', $model->amount);
+    }
+
     public function testItHandlesLargeNumbers()
     {
         $model = new class extends Model