fix: enforce mostly-safe casting

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---

Author: kgryte

lib/node_modules/@stdlib/ndarray/flatten/lib/main.js

@@ -24,6 +24,7 @@ var isPlainObject = require( '@stdlib/assert/is-plain-object' );
 var hasOwnProp = require( '@stdlib/assert/has-own-property' );
 var isndarrayLike = require( '@stdlib/assert/is-ndarray-like' );
 var isNonNegativeInteger = require( '@stdlib/assert/is-nonnegative-integer' );
+var isMostlySafeCast = require( '@stdlib/ndarray/base/assert/is-mostly-safe-data-type-cast' );
 var isOrder = require( '@stdlib/ndarray/base/assert/is-order' );
 var getShape = require( '@stdlib/ndarray/shape' );
 var getOrder = require( '@stdlib/ndarray/order' );
@@ -336,7 +337,9 @@ function flatten( x, options ) {
 			}
 		}
 		if ( hasOwnProp( options, 'dtype' ) ) {
-			// Delegate `dtype` validation to `emptyLike` during output array creation:
+			if ( !isMostlySafeCast( opts.dtype, options.dtype ) ) {
+				throw new TypeError( format( 'invalid option. First argument cannot be safely cast to the specified data type. Input data type: %s. Option: `%s`.', String( opts.dtype ), String( options.dtype ) ) );
+			}
 			opts.dtype = options.dtype;
 		}
 	}

lib/node_modules/@stdlib/ndarray/flatten/test/test.js

@@ -26,6 +26,7 @@ var tape = require( 'tape' );
 var isSameFloat64Array = require( '@stdlib/assert/is-same-float64array' );
 var isSameFloat32Array = require( '@stdlib/assert/is-same-float32array' );
 var zeros = require( '@stdlib/ndarray/zeros' );
+var empty = require( '@stdlib/ndarray/empty' );
 var ndarray = require( '@stdlib/ndarray/ctor' );
 var Float64Array = require( '@stdlib/array/float64' );
 var Float32Array = require( '@stdlib/array/float32' );
@@ -226,6 +227,38 @@ tape( 'the function throws an error if provided an invalid `dtype` option', func
 	}
 });
 
+tape( 'the function throws an error if provided a first argument which cannot be safely cast to a specified `dtype` option', function test( t ) {
+	var values;
+	var x;
+	var i;
+
+	x = empty( [ 2, 2 ], {
+		'dtype': 'bool'
+	});
+
+	values = [
+		'float64',
+		'complex128',
+		'float32',
+		'complex64',
+		'int32'
+	];
+
+	for ( i = 0; i < values.length; i++ ) {
+		t.throws( badValue( values[i] ), TypeError, 'throws an error when provided '+ values[i] );
+	}
+	t.end();
+
+	function badValue( value ) {
+		return function badValue() {
+			var opts = {
+				'dtype': value
+			};
+			flatten( x, opts );
+		};
+	}
+});
+
 tape( 'by default, the function flattens all dimensions of a provided input ndarray in lexicographic order (row-major, contiguous)', function test( t ) {
 	var expected;
 	var xbuf;